/*styles_periodic_table.css*/
/* =========================================================
   1. GLOBAL VARIABLES / RESET
   ========================================================= */

:root {
    color-scheme: dark;
    --color-bg-dark: rgb(8, 8, 8);
    --color-bg-card: rgba(34, 28, 24, 0.92);
    --color-bg-panel: rgba(20, 16, 14, 0.78);

    --color-text: #f5f0eb;
    --color-text-muted: rgb(214, 202, 190);
    --color-accent: rgb(238, 172, 96);
    --color-accent-dark: rgb(184, 128, 74);
    --color-border: rgba(220, 180, 140, 0.35);

    --radius-small: 10px;
    --radius-medium: 14px;
    --radius-large: 18px;

    --card-shadow: 0 12px 36px rgba(0, 0, 0, 0.35);
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    font-family: Arial, sans-serif;
    color: var(--color-text);
    background:
        linear-gradient(
            to top,
            rgb(170, 80, 20) 0%,
            var(--color-bg-dark) 30%,
            var(--color-bg-dark) 100%
        );
    min-height: 100vh;
}

.page {
    max-width: 1320px;
    margin: 0 auto;
    padding: 20px 24px 40px;
}


/* =========================================================
   2. SHARED COMPONENTS
   Cards, buttons, viewers, controls, notes
   ========================================================= */

.viewer-wrap {
    background:
        radial-gradient(
            circle at 50% 45%,
            rgba(255, 145, 55, 0.09),
            transparent 42%
        ),
        var(--color-bg-panel);

    border: 1px solid var(--color-border);
    border-radius: var(--radius-large);
    padding: 18px;
    box-shadow: var(--card-shadow);
}

.viewer-title {
    font-size: 22px;
    font-weight: 700;
    margin-bottom: 12px;
    color: var(--color-accent);
}

.info-card {
    background: var(--color-bg-card);
    border: 2px solid var(--color-accent-dark);
    border-radius: 16px;
    padding: 16px;
    min-height: 180px;
}

.info-card h2 {
    margin: 0 0 12px 0;
    color: var(--color-accent);
    font-size: 22px;
}

.info-line {
    margin: 8px 0;
    color: var(--color-text-muted);
    line-height: 1.4;
}

.info-label {
    color: var(--color-text);
    font-weight: 700;
}

.controls {
    display: flex;
    gap: 10px;
    flex-wrap: wrap;
    margin-bottom: 14px;
}

.footer-note {
    margin-top: 14px;
    color: var(--color-text-muted);
    font-size: 13px;
}

.hidden-card,
.graph-side-card.hidden-card,
.mix-bottom-row.hidden-card,
.compound-uses-card.hidden-card,
.experiment-lab-layout.hidden-card {
    display: none !important;
}

.app-button,
.standard-button,
.controls button,
.tab-btn,
.experiment-run-controls button,
.experiment-setup-card button,
#resetTemperatureBtn,
#resetEnergyCurveBtn {
    background: rgba(84, 68, 56, 0.95);
    color: var(--color-text);
    border: 1px solid rgb(220, 180, 140);
    border-radius: var(--radius-small);
    padding: 10px 14px;
    cursor: pointer;
    font-size: 14px;
}

.app-button:hover,
.standard-button:hover,
.controls button:hover,
.tab-btn:hover,
.experiment-run-controls button:hover,
.experiment-setup-card button:hover,
#resetTemperatureBtn:hover:not(:disabled),
#resetEnergyCurveBtn:hover:not(:disabled) {
    background: rgb(110, 84, 64);
}

#resetTemperatureBtn,
#resetEnergyCurveBtn {
    border-color: rgba(220, 180, 140, 0.75);
    border-radius: 8px;
    padding: 5px 9px;
    font-size: 12px;
}

#resetTemperatureBtn:disabled,
#resetEnergyCurveBtn:disabled {
    opacity: 0.45;
    cursor: not-allowed;
}

#atomCanvas,
#electrolysisCanvas,
#experimentLabCanvas,
#mixEnergyCurve,
#mixTemperatureCurve {
    width: 100%;
    display: block;
    border-radius: 14px;
    border: 1px solid rgba(255, 255, 255, 0.08);
}

#atomCanvas,
#electrolysisCanvas,
#experimentLabCanvas {
    height: auto;
}

#mixEnergyCurve,
#mixTemperatureCurve {
    height: 260px;
    background: rgba(5, 5, 5, 0.35);
}

#atomCanvas {
    background:
        radial-gradient(
            circle at center,
            rgba(110, 56, 22, 0.23) 0%,
            rgba(20, 20, 20, 0.04) 36%,
            rgba(15, 15, 15, 0) 60%
        );
}

#electrolysisCanvas,
#experimentLabCanvas {
    background:
        radial-gradient(
            circle at center,
            rgba(80, 150, 255, 0.10),
            transparent 48%
        ),
        rgba(5, 5, 5, 0.35);
}

#experimentLabCanvas.drag-over {
    outline: 2px dashed rgba(238, 172, 96, 0.95);
    outline-offset: 4px;
    background:
        radial-gradient(
            circle at center,
            rgba(238, 172, 96, 0.13),
            transparent 48%
        ),
        rgba(5, 5, 5, 0.35);
}

#electrolysisCard select,
#experimentLabCard select,
#electrolysisCard input[type="range"],
#experimentLabCard input[type="range"] {
    width: 100%;
    margin-top: 6px;
}

#electrolysisCard select,
#experimentLabCard select {
    background: rgba(10, 10, 10, 0.45);
    color: var(--color-text);
    border: 1px solid rgba(220, 180, 140, 0.5);
    border-radius: 8px;
    padding: 8px;
}



.experiment-apparatus-shelf .apparatus-item.hidden-apparatus {
    display: none;
}


.experiment-step-list {
    margin-top: 14px;
}


.tab-panel {
    display: none;
}

.tab-panel.active {
    display: block;
}


/* =========================================================
   CURRICULUM
   ========================================================= */

.chemistry-contents {
    padding: 40px 20px 100px;
}


.contents-heading {
    max-width: 700px;

    margin: 0 auto 44px;

    text-align: center;
}


.contents-heading h2 {
    margin: 8px 0 12px;

    font-size: 38px;

    color: #fff;
}


.contents-heading p {
    margin: 0;

    color: var(--color-text-muted);

    line-height: 1.6;
}


.curriculum-columns {
    display: grid;

    grid-template-columns: repeat(2, minmax(0, 1fr));

    gap: 26px;

    align-items: start;
}


.curriculum-year {
    min-width: 0;
}


.curriculum-year-heading {
    display: flex;

    align-items: baseline;

    gap: 10px;

    margin-bottom: 16px;

    padding-bottom: 12px;

    border-bottom: 1px solid rgba(238, 172, 96, 0.28);
}


.curriculum-year-heading span {
    color: var(--color-text-muted);

    font-size: 13px;
    font-weight: 800;

    letter-spacing: 2px;
}


.curriculum-year-heading strong {
    color: var(--color-accent);

    font-size: 34px;
}


/* =========================================================
   CHAPTER CARDS
   ========================================================= */

.curriculum-chapter {
    margin-bottom: 12px;

    overflow: hidden;

    border: 1px solid rgba(220, 180, 140, 0.24);
    border-radius: 15px;

    background:
        linear-gradient(
            135deg,
            rgba(52, 42, 34, 0.82),
            rgba(20, 16, 14, 0.78)
        );
}


.curriculum-chapter summary {
    list-style: none;

    display: grid;

    grid-template-columns: 52px 1fr auto;

    gap: 12px;

    align-items: center;

    padding: 16px;

    cursor: pointer;

    user-select: none;
}


.curriculum-chapter summary::-webkit-details-marker {
    display: none;
}


.curriculum-chapter summary:hover {
    background: rgba(238, 172, 96, 0.08);
}


.curriculum-chapter-number {
    color: rgba(238, 172, 96, 0.55);

    font-size: 27px;
    font-weight: 800;
}


.curriculum-chapter-title {
    color: #fff;

    font-size: 16px;
    font-weight: 700;
}


.curriculum-chapter-arrow {
    color: var(--color-accent);

    font-size: 18px;

    transition: transform 0.2s ease;
}


.curriculum-chapter[open] .curriculum-chapter-arrow {
    transform: rotate(180deg);
}


.curriculum-chapter-body {
    padding: 0 18px 18px 80px;

    border-top: 1px solid rgba(238, 172, 96, 0.12);
}


.curriculum-topic-list {
    margin: 16px 0;

    padding-left: 18px;

    color: var(--color-text-muted);
}


.curriculum-topic-list li {
    margin: 8px 0;

    line-height: 1.4;
}


.curriculum-feature-area {
    display: flex;

    flex-wrap: wrap;

    gap: 8px;

    margin-top: 16px;
}


.curriculum-feature-btn {
    border: 1px solid rgba(238, 172, 96, 0.65);
    border-radius: 9px;

    padding: 9px 12px;

    background: rgba(238, 172, 96, 0.13);

    color: #ffd39a;

    font-weight: 700;

    cursor: pointer;
}


.curriculum-feature-btn:hover {
    background: rgba(238, 172, 96, 0.25);
}


.curriculum-no-feature {
    color: rgba(214, 202, 190, 0.52);

    font-size: 12px;

    font-style: italic;
}


/* =========================================================
   RESPONSIVE HOME
   ========================================================= */

@media (max-width: 980px) {

    .atomic-history-hero {
        grid-template-columns: 1fr;

        min-height: auto;

        padding-top: 40px;
    }


    .atomic-history-copy {
        max-width: none;
    }


    .atomic-model-stage {
        min-height: 420px;
    }


    #atomicHistoryCanvas {
        height: 420px;
    }


    .curriculum-columns {
        grid-template-columns: 1fr;
    }
}

/* =========================================================
   4. SHARED PAGE LAYOUT
   ========================================================= */

.top,
.shared-top-layout {
    display: grid;
    gap: 24px;
    align-items: start;
}

.top {
    grid-template-columns: 1fr 320px;
    margin-bottom: 20px;
}

.shared-top-layout {
    grid-template-columns:
        minmax(0, 1fr)
        minmax(280px, 430px);

    margin-bottom: 18px;
}

.viewer-column {
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.shared-viewer,
.mix-bottom-card {
    width: 100%;
}

.shared-viewer {
    margin: 0;
}

.shared-side-card,
.graph-side-card {
    display: block;
}

/* =========================================================
   ATOMIC MODEL HISTORY
   ========================================================= */

.atomic-model-history-card {
    margin-top: 24px;
    display: grid;
    grid-template-columns: 150px minmax(0, 1fr);
    gap: 22px;
    align-items: start;

    padding: 18px;

    border: 1px solid rgba(255, 170, 80, 0.18);
    border-radius: 18px;

    background:
        linear-gradient(
            135deg,
            rgba(255, 145, 45, 0.07),
            rgba(255, 255, 255, 0.025)
        );
}


/* Scientist portrait */

.atomic-scientist-portrait-wrap {
    min-width: 0;
}

.atomic-scientist-portrait {
    display: block;

    width: 100%;
    aspect-ratio: 1 / 1;

    object-fit: cover;
    object-position: top center;

    border-radius: 14px;

    border:
        1px solid
        rgba(255, 184, 110, 0.28);

    filter: grayscale(100%);
}


.atomic-scientist-caption {
    margin-top: 10px;

    display: flex;
    flex-direction: column;
    gap: 3px;
}


.atomic-scientist-caption strong {
    color: #fff;
    font-size: 0.93rem;
}


.atomic-scientist-caption span {
    color: rgba(255, 255, 255, 0.55);
    font-size: 0.75rem;
    line-height: 1.4;
}


/* Historical text */

.atomic-model-history-copy {
    min-width: 0;
}


.atomic-history-label {
    margin-bottom: 8px;

    color: #e99845;

    font-size: 0.69rem;
    font-weight: 800;

    letter-spacing: 0.14em;
}


.atomic-model-history-copy > p {
    margin: 0;

    color: rgba(255, 255, 255, 0.76);

    font-size: 0.9rem;
    line-height: 1.65;
}


/* Evidence / key idea */

.atomic-model-evidence {
    margin-top: 16px;

    padding: 12px 14px;

    border-left: 3px solid #dc8a3b;

    border-radius: 0 10px 10px 0;

    background: rgba(255, 151, 59, 0.07);
}


.atomic-evidence-label {
    display: block;

    margin-bottom: 5px;

    color: #f1a45a;

    font-size: 0.65rem;
    font-weight: 800;

    letter-spacing: 0.12em;
}


.atomic-model-evidence p {
    margin: 0;

    color: rgba(255, 255, 255, 0.68);

    font-size: 0.82rem;
    line-height: 1.5;
}


/* Smaller screens */

@media (max-width: 750px) {

    .atomic-model-history-card {
        grid-template-columns: 95px minmax(0, 1fr);
        gap: 14px;
    }

}

.atomic-history-hero {
    display: flex;
    flex-direction: column;
    gap: 28px;
    width: 100%;
}

.atomic-hero-top {
    width: 100%;
}

.atomic-hero-title {
    margin: 10px 0 0;
    max-width: 100%;
    color: #ffffff;
    font-size: clamp(3.4rem, 6.2vw, 5.6rem);
    line-height: 0.92;
    font-weight: 800;
    letter-spacing: -0.03em;
}

.atomic-hero-main {
    display: grid;
    grid-template-columns: minmax(360px, 1fr) minmax(420px, 0.95fr);
    gap: 34px;
    align-items: start;
}

.atomic-history-copy {
    min-width: 0;
}

.atomic-model-meta {
    margin-bottom: 12px;
    font-size: 1.05rem;
}

#atomicModelName {
    margin: 0 0 16px;
    font-size: clamp(2rem, 3.2vw, 3rem);
    line-height: 1.05;
    color: #ffad5a;
}

#atomicModelDescription {
    margin: 0 0 24px;
    max-width: 640px;
    font-size: 1.1rem;
    line-height: 1.6;
    color: rgba(255, 255, 255, 0.85);
}

.atomic-model-stage {
    position: relative;
    display: block;
    width: 100%;
    height: 420px;
    margin-top: 52px; /* pushes viewer down so it lines up near the model name */
    padding: 24px;
    border: 1px solid rgba(255, 145, 45, 0.22);
    border-radius: 28px;
    background:
        radial-gradient(circle at center, rgba(255, 120, 35, 0.10), transparent 58%),
        rgba(15, 8, 4, 0.72);
    overflow: hidden;
    cursor: pointer;
}

#atomicHistoryCanvas {
    display: block;
    width: 100%;
    height: 100%;
}

.atomic-click-hint {
    position: absolute;
    left: 50%;
    bottom: 16px;
    transform: translateX(-50%);
    font-size: 0.9rem;
    color: rgba(255, 255, 255, 0.72);
    pointer-events: none;
}

.atomic-model-history-card {
    margin-top: 18px;
    display: grid;
    grid-template-columns: 140px minmax(0, 1fr);
    gap: 18px;
    align-items: start;
    padding: 18px;
    border: 1px solid rgba(255, 170, 80, 0.16);
    border-radius: 18px;
    background: rgba(255, 145, 45, 0.05);
}
/* =========================================================
   5. PERIODIC TABLE
   ========================================================= */

/* table-wrap, table-grid, tile, radius-dot, legend here */

        .table-wrap {
            margin-top: 10px;
            background: rgba(20, 16, 14, 0.72);
            border: 1px solid rgba(220, 180, 140, 0.35);
            border-radius: 18px;
            padding: 18px;
            overflow-x: auto;
            container-type: inline-size;
        }

        .table-grid {
            display: grid;
            grid-template-columns: repeat(18, minmax(0, 1fr));
            gap: 4px;
        }

        .tile {
            min-height: 72px;
            border-radius: 10px;
            border: 1px solid rgba(255,255,255,0.10);
            color: #f5f0eb;
            cursor: pointer;
            padding: 4px;
            position: relative;
            overflow: hidden;
            transition: transform 0.12s ease, border-color 0.12s ease, box-shadow 0.12s ease;
        }

        .tile-number {
            position: absolute;
            top: 6px;
            left: 8px;
            z-index: 3;
            font-size: 11px;
            font-weight: 700;
            line-height: 1;
            opacity: 0.95;
            pointer-events: none;
        }

        .tile-protons {
            position: absolute;
            top: 6px;
            left: 50%;
            transform: translateX(-50%);
            z-index: 3;
            font-size: 11px;
            font-weight: 700;
            line-height: 1;
            opacity: 0.95;
            pointer-events: none;
            text-align: center;
        }

        .tile-symbol {
            position: absolute;
            top: 24px;
            left: 50%;
            transform: translateX(-50%);
            z-index: 3;
            line-height: 1;
            font-weight: 700;
            font-size: 16px;
            text-align: center;
            pointer-events: none;
            text-shadow: 0 1px 2px rgba(0,0,0,0.35);
        }

        .tile-mass {
            position: absolute;
            bottom: 6px;
            left: 50%;
            transform: translateX(-50%);
            z-index: 3;
            font-size: 10px;
            font-weight: 600;
            line-height: 1;
            opacity: 0.88;
            pointer-events: none;
            text-align: center;
            white-space: nowrap;
        }

        .radius-dot {
            position: absolute;
            left: 50%;
            top: 50%;
            transform: translate(-50%, -50%);
            width: 18px;
            height: 18px;
            border-radius: 999px;
            background: rgba(255, 255, 255, 0.11);
            box-shadow:
                inset 0 0 0 1px rgba(255,255,255,0.08),
                0 0 14px rgba(255,255,255,0.04);
            z-index: 1;
            pointer-events: none;
        }

        .tile.no-radius .radius-dot {
            opacity: 0.10;
        }

        .tile:hover {
            transform: translateY(-1px);
            border-color: rgba(245, 220, 190, 0.9);
            box-shadow: 0 6px 18px rgba(0,0,0,0.2);
        }

        .tile.selected {
            outline: 2px solid rgba(255, 235, 215, 0.9);
        }

        .block-s { background: rgb(210, 120, 120); }
        .block-p { background: rgb(120, 170, 220); }
        .block-d { background: rgb(220, 180, 95); color: #2b1f12; }
        .block-f { background: rgb(180, 130, 200); }
        .block-unknown { background: rgb(100, 100, 100); }

        .legend {
    display: flex;
    flex-wrap: wrap;
    gap: 16px;
    margin: 0 0 16px;
    color: var(--color-text-muted);
    font-size: 14px;
}

.tile.metalloid {
    outline: 3px solid #8b5a2b;
    outline-offset: -3px;
}

.metalloid-legend-box {
    background: transparent;
    border: 3px solid #8b5a2b;
    box-sizing: border-box;
}

.legend-item {
    display: inline-flex;
    align-items: center;
    gap: 8px;
}

.legend-box {
    display: inline-block;
    width: 14px;
    height: 14px;
    border-radius: 4px;
}

/* Tiles shrink to fit the card; compact layout keeps number + symbol. */
@container (max-width: 899px) {
    .table-grid {
        gap: 3px;
    }

    .tile {
        min-height: 0;
        aspect-ratio: 1 / 1.1;
        padding: 2px;
        border-radius: 7px;
    }

    .tile-protons {
        top: 3px;
        font-size: clamp(6px, 1.1cqw, 10px);
    }

    .tile-symbol {
        top: 60%;
        transform: translate(-50%, -50%);
        font-size: clamp(9px, 1.8cqw, 15px);
    }

    .tile-mass,
    .radius-dot {
        display: none;
    }
}

/* Phones: keep the table readable and scroll it inside the card. */
@container (max-width: 520px) {
    .table-grid {
        min-width: 560px;
    }
}
/* =========================================================
   6. ELEMENT INFO CARD
   ========================================================= */

/* element uses details, element-use-item here */

.element-use-text {
    display: flex;
    flex-direction: column;
    gap: 2px;
}

.element-use-name {
    color: #ffd39a;
    font-size: 13px;
    font-weight: 700;
}

.element-use-formula {
    color: var(--color-text-muted);
    font-size: 12px;
}

.element-history-details,
.element-uses-details {
    margin-top: 14px;
    padding-top: 10px;
    border-top: 1px solid rgba(255, 180, 90, 0.14);
}

.element-history-details summary,
.element-uses-details summary {
    color: var(--color-accent);
    font-weight: 700;
    cursor: pointer;
    user-select: none;
}

.compound-uses-card {
    min-height: 180px;
}

.compound-uses-section,
.frequent-compounds {
    margin-top: 14px;
    padding-top: 12px;
    border-top: 1px solid rgba(255, 180, 90, 0.14);
}

.compound-uses-title,
.frequent-title {
    color: var(--color-accent);
    font-weight: 700;
    margin-bottom: 10px;
}

.compound-uses-grid,
.element-uses-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: 12px;
}

.frequent-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 10px;
}

.compound-use-item,
.element-use-item,
.frequent-compound {
    background: rgba(255, 255, 255, 0.06);
    border: 1px solid rgba(220, 180, 140, 0.28);
    border-radius: 12px;
    display: flex;
    align-items: center;
}

.compound-use-item {
    gap: 12px;
    padding: 10px;
}

.element-use-item {
    gap: 10px;
    padding: 9px;
}

.frequent-compound {
    gap: 8px;
    padding: 8px;
    color: var(--color-text);
    text-align: left;
    cursor: pointer;
}

.frequent-compound:hover {
    background: rgba(238, 172, 96, 0.14);
    border-color: rgba(238, 172, 96, 0.75);
}

.compound-use-item img {
    width: 88px;
    height: 88px;
}

.element-use-item img {
    width: 62px;
    height: 62px;
}

.frequent-compound img {
    width: 38px;
    height: 38px;
    object-fit: contain;
}

.compound-use-item img,
.element-use-item img,
.frequent-compound img {
    border-radius: 10px;
    background: rgba(0, 0, 0, 0.18);
    flex-shrink: 0;
}

.compound-use-item img,
.element-use-item img {
    object-fit: cover;
}

.compound-use-item span,
.frequent-compound span {
    color: #ffd39a;
    font-weight: 700;
}

.compound-use-item span {
    font-size: 14px;
    line-height: 1.3;
}

.frequent-compound span {
    font-size: 13px;
}

/* =========================================================
   7. MIXING LAB
   ========================================================= */

/* mixInfoCard, mixBottomRow, graph card, energy curve, temperature curve here */

.mixing-layout {
    display: grid;
    grid-template-columns: 1fr 320px;
    gap: 20px;
    margin-bottom: 20px;
}

.mixer-main-card {
    min-height: 360px;
}

#mixInfoCard {
    position: relative;
}

#mixInfoCard .info-line {
    margin: 7px 0;
    padding-bottom: 6px;
    border-bottom: 1px solid rgba(255, 180, 90, 0.08);
}

#mixInfoCard .info-line:last-of-type {
    border-bottom: none;
}

#mixInfoCard .info-label {
    color: #fff1df;
}

.mix-card-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 10px;
    margin-bottom: 10px;
}

.mix-card-header h2 {
    margin: 0;
}

.mix-help-btn {
    width: 26px;
    height: 26px;
    border-radius: 999px;
    border: 1px solid rgb(220, 180, 140);
    background: rgb(184, 128, 74);
    color: #1d120b;
    font-size: 15px;
    font-weight: 800;
    line-height: 1;
    cursor: pointer;
    flex: 0 0 auto;
}

.mix-help-btn:hover {
    background: var(--color-accent);
}

.mix-help-popup {
    position: absolute;

    /* directly underneath the ? button area */
    top: 52px;
    right: 14px;

    z-index: 901;

    width: 320px;
    max-width: calc(100% - 28px);

    background: rgba(34, 28, 24, 0.98);
    border: 2px solid rgb(184, 128, 74);
    border-radius: 16px;
    color: #f5f0eb;

    box-shadow: 0 12px 36px rgba(0,0,0,0.45);
    overflow: hidden;
}

.mix-help-header {
    background: rgba(184, 128, 74, 0.95);
    color: #1d120b;
    padding: 10px 12px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.mix-help-header button {
    background: transparent;
    border: none;
    color: #1d120b;
    font-size: 24px;
    cursor: pointer;
}

.mix-bottom-row {
    display: grid;
    grid-template-columns: minmax(360px, 1fr) minmax(260px, 340px);
    gap: 16px;
    align-items: start;
}

.mix-help-body {
    padding: 14px;
}
/* ---------- Mixing Lab bond type hyperlink ---------- */

#mixType {
    position: relative;
    display: inline-block;
}

.mix-bond-type-link {
    position: relative;

    color: #ffd39a;
    font-weight: 700;

    text-decoration: underline;
    text-decoration-style: dotted;
    text-underline-offset: 3px;

    cursor: help;
}

.mix-bond-type-link:hover {
    color: var(--color-accent);
}

/* Tooltip */

.mix-bond-type-link::after {
    content: attr(data-tooltip);

    position: absolute;
    left: 50%;
    bottom: calc(100% + 10px);

    transform: translateX(-50%) translateY(4px);

    width: 280px;
    padding: 10px 12px;

    background: rgba(20, 16, 14, 0.98);
    border: 1px solid rgba(238, 172, 96, 0.75);
    border-radius: 10px;

    color: #f5f0eb;
    font-size: 12px;
    font-weight: 400;
    line-height: 1.45;

    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.4);

    opacity: 0;
    visibility: hidden;
    pointer-events: none;

    transition:
        opacity 0.15s ease,
        transform 0.15s ease;

    z-index: 1000;
}

/* Little tooltip arrow */

.mix-bond-type-link::before {
    content: "";

    position: absolute;
    left: 50%;
    bottom: calc(100% + 4px);

    transform: translateX(-50%);

    border: 6px solid transparent;
    border-top-color: rgba(238, 172, 96, 0.75);

    opacity: 0;
    visibility: hidden;

    z-index: 1001;
}

.mix-bond-type-link:hover::after,
.mix-bond-type-link:hover::before {
    opacity: 1;
    visibility: visible;
}

.mix-bond-type-link:hover::after {
    transform: translateX(-50%) translateY(0);
}

#mixResult,
#mixFormula,
#mixType,
#mixBondStrength,
#mixBondForce,
#mixStability {
    color: #ffd39a;
    font-weight: 700;
}

.curve-dropdown {
    margin-top: 12px;
    border-radius: 14px;
    border: 1px solid rgba(220, 180, 140, 0.32);
    background: rgba(0, 0, 0, 0.22);
    overflow: hidden;
}

.curve-dropdown summary {
    list-style: none;
    cursor: pointer;
    padding: 12px 14px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 10px;
    color: rgb(238, 172, 96);
    font-weight: 700;
    user-select: none;
}

.curve-dropdown summary::-webkit-details-marker {
    display: none;
}

.curve-dropdown summary::after {
    content: "▾";
    font-size: 16px;
    transition: transform 0.18s ease;
}

.curve-dropdown[open] summary::after {
    transform: rotate(180deg);
}

.curve-dropdown summary small {
    color: rgb(214, 202, 190);
    font-size: 11px;
    font-weight: 500;
    opacity: 0.85;
}

.curve-dropdown .energy-curve-box {
    margin-top: 0;
    border-left: none;
    border-right: none;
    border-bottom: none;
    border-radius: 0;
    background: rgba(0, 0, 0, 0.30);
}

.energy-curve-title {
    font-weight: 700;
    color: rgb(238, 172, 96);
    margin-bottom: 8px;
    font-size: 14px;
}

.energy-curve-note {
    margin-top: 6px;
    font-size: 12px;
    color: rgb(214, 202, 190);
    line-height: 1.35;
}

.energy-slider-row {
    margin-top: 8px;
    display: grid;
    grid-template-columns: auto 1fr auto auto;
    gap: 8px;
    align-items: center;
    font-size: 12px;
    color: rgb(214, 202, 190);
}

.energy-slider-row input[type="range"] {
    width: 100%;
    accent-color: rgb(90, 230, 120);
}

.energy-curve-subtitle {
    margin-top: 12px;
    margin-bottom: 6px;
    color: rgb(238, 172, 96);
    font-size: 13px;
    font-weight: 700;
}

.energy-curve-box {
    margin-top: 14px;
    padding: 12px;
    border-radius: 14px;
    background: rgba(0, 0, 0, 0.32);
    border: 1px solid rgba(220, 180, 140, 0.32);
    box-shadow: inset 0 0 18px rgba(0,0,0,0.22);
}

#mixTemperatureSlider {
    accent-color: rgb(255, 190, 90);
}

#mixDistanceValue,
#mixTemperatureValue {
    font-weight: 700;
    white-space: nowrap;
}

#mixDistanceValue {
    color: rgb(90, 230, 120);
}

#mixTemperatureValue {
    color: rgb(255, 190, 90);
}
 
.atom-history-content {
    padding-top: 4px;
}

.atom-history-description {
    margin-top: 10px;
    padding-top: 10px;

    border-top: 1px solid rgba(255, 180, 90, 0.10);

    color: var(--color-text-muted);
    line-height: 1.5;
}

.glossary-top-btn {
    margin-left: auto;

    padding: 9px 16px;

    border: 1px solid rgba(255, 170, 60, 0.45);
    border-radius: 10px;

    background:
        linear-gradient(
            180deg,
            rgba(255, 150, 40, 0.16),
            rgba(255, 110, 20, 0.08)
        );

    color: #fff;

    font-size: 14px;
    font-weight: 700;

    cursor: pointer;

    transition:
        background 0.18s ease,
        border-color 0.18s ease,
        transform 0.18s ease;
}

.glossary-top-btn:hover {
    border-color: rgba(255, 170, 60, 0.85);

    background:
        linear-gradient(
            180deg,
            rgba(255, 150, 40, 0.28),
            rgba(255, 110, 20, 0.14)
        );

    transform: translateY(-1px);
}

.glossary-overlay {
    position: fixed;
    inset: 0;

    z-index: 10000;

    display: none;
    align-items: center;
    justify-content: center;

    padding: 30px;

    background: rgba(0, 0, 0, 0.68);
    backdrop-filter: blur(5px);
}

.glossary-overlay.is-open {
    display: flex;
}

.glossary-window {
    width: min(1000px, 94vw);
    height: min(720px, 86vh);

    display: flex;
    flex-direction: column;

    overflow: hidden;

    border:
        1px solid
        rgba(255, 155, 50, 0.34);

    border-radius: 18px;

    background:
        linear-gradient(
            145deg,
            rgba(24, 24, 27, 0.98),
            rgba(10, 10, 12, 0.99)
        );

    box-shadow:
        0 25px 80px
        rgba(0, 0, 0, 0.55);
}


/* -------------------------
   Header
-------------------------- */

.glossary-header {
    flex: 0 0 auto;

    display: flex;
    align-items: center;
    justify-content: space-between;

    padding: 18px 22px;

    border-bottom:
        1px solid
        rgba(255, 255, 255, 0.09);

    background:
        linear-gradient(
            90deg,
            rgba(255, 130, 30, 0.12),
            transparent
        );
}

.glossary-header h2 {
    margin: 2px 0 0;

    color: #fff;
}

.glossary-header-label {
    color: #ff9d42;

    font-size: 11px;
    font-weight: 800;

    letter-spacing: 1.2px;
    text-transform: uppercase;
}

.glossary-close-btn {
    width: 38px;
    height: 38px;

    border: 0;
    border-radius: 10px;

    background: rgba(255, 255, 255, 0.08);

    color: #fff;

    font-size: 25px;

    cursor: pointer;
}

.glossary-close-btn:hover {
    background: rgba(255, 110, 50, 0.2);
}


/* -------------------------
   Main area
-------------------------- */

.glossary-body {
    flex: 1;
    min-height: 0;

    display: grid;
    grid-template-columns: 260px 1fr;
}


/* -------------------------
   Left term list
-------------------------- */

.glossary-sidebar {
    min-height: 0;

    display: flex;
    flex-direction: column;

    padding: 15px;

    border-right:
        1px solid
        rgba(255, 255, 255, 0.08);

    background:
        rgba(0, 0, 0, 0.2);
}

.glossary-search {
    width: 100%;

    box-sizing: border-box;

    margin-bottom: 12px;

    padding: 11px 12px;

    border:
        1px solid
        rgba(255, 255, 255, 0.14);

    border-radius: 9px;

    outline: none;

    background:
        rgba(255, 255, 255, 0.06);

    color: #fff;
}

.glossary-search:focus {
    border-color:
        rgba(255, 155, 60, 0.7);
}

.glossary-term-list {
    flex: 1;

    min-height: 0;

    overflow-y: auto;

    display: flex;
    flex-direction: column;

    gap: 6px;
}

.glossary-term-btn {
    width: 100%;

    padding: 10px 11px;

    border: 1px solid transparent;
    border-radius: 8px;

    background: transparent;

    color: #ddd;

    text-align: left;

    cursor: pointer;
}

.glossary-term-btn:hover {
    background:
        rgba(255, 255, 255, 0.06);
}

.glossary-term-btn.is-selected {
    border-color:
        rgba(255, 150, 50, 0.4);

    background:
        rgba(255, 135, 35, 0.12);

    color: #ffad5c;
}


/* -------------------------
   Definition
-------------------------- */

.glossary-content {
    min-width: 0;

    padding: 28px 32px 40px;

    overflow-y: auto;
}

.glossary-category {
    display: inline-block;

    margin-bottom: 8px;

    padding: 4px 9px;

    border-radius: 999px;

    background:
        rgba(255, 145, 40, 0.13);

    color: #ffad5c;

    font-size: 12px;
    font-weight: 800;

    text-transform: uppercase;
    letter-spacing: 0.6px;
}

.glossary-content > h2 {
    margin: 0 0 10px;

    color: #fff;

    font-size: 30px;
}

.glossary-short-definition {
    margin: 0 0 24px;

    color: #ffcf9f;

    font-size: 16px;
    line-height: 1.6;
}

.glossary-explanation p {
    color: #ddd;

    line-height: 1.75;
}

.glossary-section {
    margin-top: 26px;
}

.glossary-section h3 {
    margin-bottom: 10px;

    color: #fff;
}

.glossary-section li {
    margin-bottom: 7px;

    color: #d9d9d9;

    line-height: 1.5;
}

.glossary-examples {
    display: flex;
    flex-wrap: wrap;

    gap: 8px;
}

.glossary-example {
    padding: 7px 11px;

    border:
        1px solid
        rgba(255, 255, 255, 0.1);

    border-radius: 8px;

    background:
        rgba(255, 255, 255, 0.05);

    color: #eee;
}


/* -------------------------
   Clickable glossary words
-------------------------- */

.glossary-link {
    padding: 0;

    border: 0;
    border-bottom:
        1px dashed
        rgba(255, 165, 75, 0.8);

    background: transparent;

    color: #ffad5c;

    font: inherit;

    cursor: pointer;
}

.glossary-link:hover {
    color: #ffc182;

    border-bottom-style: solid;
}


/* -------------------------
   Mobile
-------------------------- */

@media (max-width: 750px) {

    .glossary-overlay {
        padding: 12px;
    }

    .glossary-window {
        width: 100%;
        height: 92vh;
    }

    .glossary-body {
        grid-template-columns: 1fr;
    }

    .glossary-sidebar {
        max-height: 180px;

        border-right: 0;

        border-bottom:
            1px solid
            rgba(255, 255, 255, 0.08);
    }
}

/* =========================================================
   9. EXPERIMENT LAB
   ========================================================= */

/* experiment-lab-layout, apparatus shelf, beaker, bottle, battery here */
.electrode-result-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: 12px;
    margin-top: 14px;
}

.electrode-result {
    padding: 12px;
    border-radius: 14px;
    background: rgba(255, 255, 255, 0.06);
    border: 1px solid rgba(255, 255, 255, 0.12);
}

.electrode-result h3 {
    margin: 0 0 8px 0;
    font-size: 15px;
    color: rgb(245, 230, 210);
}

.cathode-result {
    border-left: 4px solid rgba(120, 190, 255, 0.9);
}

.anode-result {
    border-left: 4px solid rgba(255, 150, 110, 0.9);
}

#experimentCathodeEquation,
#experimentAnodeEquation {
    font-family: "Consolas", "Courier New", monospace;
    color: rgb(255, 232, 170);
}

.experiment-toolbar {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    margin-bottom: 14px;
}

.experiment-tool {
    width: 100%;
    padding: 10px 14px;
    color: var(--color-text);
    background: rgba(84, 68, 56, 0.95);
    border: 1px solid rgb(220, 180, 140);
    border-radius: 12px;
    font-size: 14px;
    text-align: left;
    cursor: grab;
    user-select: none;
}

.experiment-tool:hover {
    background: rgb(110, 84, 64);
}

.experiment-tool.active {
    background: var(--color-accent);
    color: #1d120b;
    font-weight: 700;
}

.experiment-tool:active {
    cursor: grabbing;
}

.experiment-video-section {
    margin-top: 14px;
    padding-top: 12px;
    border-top: 1px solid rgba(255, 180, 90, 0.14);
}

.experiment-video-header {
    margin-bottom: 10px;
}

.experiment-video-header h3 {
    margin: 0 0 4px;
    color: var(--color-accent);
    font-size: 17px;
}

.experiment-video-header span,
.experiment-video-note {
    color: var(--color-text-muted);
    font-size: 13px;
    line-height: 1.35;
}

.experiment-step.step-latest-complete {
    border-color: rgba(255, 210, 95, 0.95);
    background:
        linear-gradient(
            90deg,
            rgba(238, 172, 96, 0.34),
            rgba(70, 130, 85, 0.22)
        );
    box-shadow:
        0 0 0 1px rgba(238, 172, 96, 0.25),
        0 0 18px rgba(238, 172, 96, 0.22);
    transform: translateX(3px);
}

.experiment-step.step-latest-complete .step-number {
    background: rgb(238, 172, 96);
    color: #1d120b;
}


        .primary-run-btn {
            background: rgb(238, 172, 96) !important;
            color: #1d120b !important;
            font-weight: 700;
        }

        .experiment-step-list {
            display: grid;
            gap: 8px;
            margin-bottom: 14px;
        }

        .experiment-step {
            display: flex;
            align-items: center;
            gap: 10px;
            color: rgb(214, 202, 190);
            padding: 8px 10px;
            border-radius: 10px;
            background: rgba(255,255,255,0.05);
            border: 1px solid rgba(220, 180, 140, 0.18);
        }

        .step-number {
            width: 24px;
            height: 24px;
            border-radius: 999px;
            display: inline-flex;
            align-items: center;
            justify-content: center;
            background: rgb(184, 128, 74);
            color: #1d120b;
            font-weight: 800;
            font-size: 13px;
            flex: 0 0 auto;
        }

        .vertical-toolbar {
            display: grid;
            grid-template-columns: 1fr;
            gap: 8px;
            margin-bottom: 16px;
        }

        .experiment-field {
            margin-top: 14px;
        }

        .experiment-field label {
            display: block;
            color: #fff1df;
            font-weight: 700;
            margin-bottom: 6px;
        }

        .experiment-slider-row {
            display: grid;
            grid-template-columns: 1fr auto;
            gap: 10px;
            align-items: center;
        }

        #experimentVoltageValue {
            color: #ffd39a;
            font-weight: 700;
            white-space: nowrap;
        }

        .experiment-current-tool {
            margin-top: 14px;
            padding-top: 12px;
            border-top: 1px solid rgba(255, 180, 90, 0.14);
            color: rgb(214, 202, 190);
        }

        .experiment-main-viewer {
            min-width: 0;
        }

        .experiment-side-column {
            display: flex;
            flex-direction: column;
            gap: 18px;
        }

        .experiment-video-frame-wrap {
            position: relative;
            width: 100%;
            aspect-ratio: 16 / 9;
            border-radius: 12px;
            overflow: hidden;
            background: rgba(0, 0, 0, 0.38);
            border: 1px solid rgba(220, 180, 140, 0.28);
        }

        #experimentReferenceVideo {
            width: 100%;
            height: 100%;
            border: 0;
            display: block;
        }

        .experiment-video-frame-wrap.empty-video {
            display: flex;
            align-items: center;
            justify-content: center;
        }

        .experiment-video-frame-wrap.empty-video::before {
            content: "No video selected";
            color: rgba(245, 240, 235, 0.7);
            font-size: 14px;
            position: absolute;
            z-index: 1;
        }

        .experiment-video-frame-wrap.empty-video iframe {
            display: none;
        }

        .experiment-video-frame-wrap:not(.empty-video) iframe {
            display: block;
        }

        .experiment-video-header {
            margin-bottom: 10px;
        }

        .experiment-video-header span,
        .experiment-video-note {
            color: rgb(214, 202, 190);
            font-size: 13px;
            line-height: 1.35;
        }

        .experiment-video-note {
            margin-top: 8px;
            font-size: 12px;
        }

.experiment-step.step-complete {
    border-color: rgba(110, 220, 150, 0.65);
    background: rgba(70, 130, 85, 0.22);
}

.experiment-step.step-complete .step-number {
    background: rgba(95, 210, 130, 0.95);
    color: #102014;
    font-weight: 800;
}

.apparatus-shelf {
    display: grid;
    grid-template-columns: 1fr;
    gap: 8px;
    margin-bottom: 16px;
}

.apparatus-item {
    display: grid;
    grid-template-columns: 48px 1fr;
    align-items: center;
    column-gap: 8px;
    min-height: 64px;
    padding: 6px 10px;
    border-radius: 14px;
    border: 1px solid rgba(220, 180, 140, 0.35);
    background: rgba(255, 255, 255, 0.05);
    cursor: default;
    user-select: none;
    transition:
        transform 0.14s ease,
        border-color 0.14s ease,
        background 0.14s ease,
        box-shadow 0.14s ease;
}

.apparatus-item:hover {
    transform: translateY(-1px);
}

.apparatus-item.active {
    background: rgba(238, 172, 96, 0.16);
    border-color: rgba(238, 172, 96, 0.95);
    box-shadow: 0 0 0 1px rgba(238, 172, 96, 0.25) inset;
}

.apparatus-visual {
    position: relative;
    justify-self: center;
    width: 48px;
    height: 48px;
    cursor: grab;
}

.apparatus-visual:active {
    cursor: grabbing;
}

.apparatus-name {
    color: #ffd39a;
    font-size: 13px;
    font-weight: 700;
    line-height: 1.2;
    cursor: default;
    user-select: none;
}

        /* ---------- Beaker ---------- */

        .beaker-visual::before {
            content: "";
            position: absolute;

            left: 50%;
            top: 8px;
            transform: translateX(-50%);

            width: 28px;
            height: 32px;

            border-left: 2px solid rgba(220, 235, 255, 0.85);
            border-right: 2px solid rgba(220, 235, 255, 0.85);
            border-bottom: 2px solid rgba(220, 235, 255, 0.85);
            border-radius: 0 0 8px 8px;
        }

        /* ---------- Solution bottle ---------- */

        .bottle-cap {
            position: absolute;

            left: 50%;
            top: 3px;
            transform: translateX(-50%);

            width: 14px;
            height: 7px;

            border-radius: 4px 4px 2px 2px;
            background: rgba(215, 215, 215, 0.9);
        }

        .bottle-neck {
            position: absolute;

            left: 50%;
            top: 10px;
            transform: translateX(-50%);

            width: 10px;
            height: 8px;

            background: rgba(235, 245, 255, 0.62);
            border-left: 2px solid rgba(235, 245, 255, 0.85);
            border-right: 2px solid rgba(235, 245, 255, 0.85);
        }

        .bottle-body {
            position: absolute;

            left: 50%;
            top: 17px;
            transform: translateX(-50%);

            width: 34px;
            height: 29px;

            border-radius: 8px 8px 10px 10px;
            background: rgba(235, 245, 255, 0.20);
            border: 2px solid rgba(235, 245, 255, 0.82);
            overflow: hidden;
        }

        .bottle-liquid {
            position: absolute;
            left: 0;
            right: 0;
            bottom: 0;
            height: 48%;
            background: rgba(80, 150, 255, 0.42);
        }

        .bottle-label {
            position: absolute;

            left: 3px;
            right: 3px;
            top: 5px;

            z-index: 2;
            background: rgba(255,255,255,0.82);
            color: #1d120b;

            border-radius: 4px;
            font-size: 6px;
            font-weight: 700;
            line-height: 1.05;
            text-align: center;
            padding: 2px;
            overflow: hidden;
        }

        /* ---------- Electrodes ---------- */

        .electrode-rod {
            position: absolute;
            top: 7px;

            width: 7px;
            height: 34px;

            border-radius: 6px;
            background: rgba(70, 70, 70, 0.95);
            box-shadow: inset 0 0 0 1px rgba(255,255,255,0.10);
        }

        .electrode-rod.left {
            left: 14px;
        }

        .electrode-rod.right {
            right: 14px;
        }

        /* ---------- Battery ---------- */

        .battery-body {
            position: absolute;

            left: 50%;
            top: 14px;
            transform: translateX(-50%);

            width: 34px;
            height: 22px;

            border-radius: 6px;
            background: linear-gradient(
                to bottom,
                rgba(90, 90, 90, 0.95),
                rgba(55, 55, 55, 0.95)
            );

            border: 2px solid rgba(255,255,255,0.14);
            color: #ffd39a;
            font-weight: 800;
            font-size: 11px;
        }

        .battery-plus,
        .battery-minus {
            position: absolute;
            top: 3px;
        }

        .battery-plus {
            left: 7px;
        }

        .battery-minus {
            right: 7px;
        }

        .battery-tip {
            position: absolute;

            left: 41px;
            top: 20px;

            width: 5px;
            height: 9px;

            border-radius: 0 3px 3px 0;
            background: rgba(220, 220, 220, 0.9);
        }

/* =========================================================
   10. QUESTIONS POPUP
   ========================================================= */

/* question mini app here */
        .question-float-btn {
            position: fixed;
            right: 24px;
            bottom: 24px;
            z-index: 1000;
            background: rgb(238, 172, 96);
            color: #1d120b;
            border: none;
            border-radius: 999px;
            padding: 14px 18px;
            font-weight: 700;
            cursor: pointer;
            box-shadow: 0 8px 24px rgba(0,0,0,0.35);
        }

        .question-mini-app {
            position: fixed;
            right: 24px;
            bottom: 88px;
            width: 340px;
            max-width: calc(100vw - 32px);
            height: 420px;
            max-height: calc(100vh - 120px);
            z-index: 1200;

            background: rgba(34, 28, 24, 0.98);
            border: 2px solid rgb(184, 128, 74);
            border-radius: 18px;
            color: #f5f0eb;
            box-shadow: 0 12px 40px rgba(0,0,0,0.45);

            overflow: hidden;
        }

        .question-mini-app.hidden {
            display: none;
        }

        .question-mini-header {
            height: 46px;
            background: rgba(184, 128, 74, 0.95);
            color: #1d120b;
            display: flex;
            align-items: center;
            justify-content: space-between;
            padding: 0 12px;
            font-weight: 700;
            cursor: grab;
            user-select: none;
        }

        .question-mini-header:active {
            cursor: grabbing;
        }

        .question-mini-header button {
            background: transparent;
            border: none;
            color: #1d120b;
            font-size: 26px;
            cursor: pointer;
            line-height: 1;
        }

        .question-mini-body {
            height: calc(100% - 46px);
            overflow-y: auto;
            padding: 16px;
        }

        .question-item {
            margin-bottom: 16px;
            padding: 12px;
            border-radius: 12px;
            background: rgba(255,255,255,0.06);
            border: 1px solid rgba(255,255,255,0.08);
        }

        .question-item strong {
            color: rgb(238, 172, 96);
        }

        .question-answer {
            width: 100%;
            margin-top: 8px;
            min-height: 70px;
            resize: vertical;
            border-radius: 10px;
            border: 1px solid rgba(220, 180, 140, 0.5);
            background: rgba(10, 10, 10, 0.35);
            color: #f5f0eb;
            padding: 10px;
            font-family: Arial, sans-serif;
        }

/* =========================================================
   FLOATING / POPOUT REFERENCE VIDEO
   ========================================================= */

    .experiment-video-card-titlebar {
        display: flex;
        align-items: center;
        justify-content: space-between;
        gap: 10px;
        margin-bottom: 12px;
    }

    .experiment-video-card-titlebar h2 {
        margin: 0;
    }

    .experiment-video-actions {
        display: flex;
        gap: 6px;
    }

    .experiment-video-actions button {
        width: 30px;
        height: 30px;
        border-radius: 8px;
        border: 1px solid rgba(220, 180, 140, 0.65);
        background: rgba(84, 68, 56, 0.95);
        color: var(--color-text);
        cursor: pointer;
        font-size: 16px;
        line-height: 1;
    }

    .experiment-video-actions button:hover {
        background: rgb(110, 84, 64);
    }

    #experimentVideoCloseBtn {
        display: none;
    }

    .experiment-video-card.video-popout {
        position: fixed;
        z-index: 2000;

        width: min(760px, calc(100vw - 32px));
        height: auto;

        min-width: 360px;
        min-height: 320px;

        max-width: calc(100vw - 32px);
        max-height: calc(100vh - 32px);

        overflow: auto;
        resize: both;

        left: 50%;
        top: 50%;
        transform: translate(-50%, -50%);

        box-shadow: 0 22px 70px rgba(0, 0, 0, 0.65);
    }

    .experiment-video-card.video-popout .experiment-video-frame-wrap {
        width: 100%;
        aspect-ratio: 16 / 9;
    }

    .experiment-video-card.video-popout iframe {
        width: 100%;
        height: 100%;
    }
    .experiment-video-card.video-popout .experiment-video-card-titlebar {
        cursor: move;
        user-select: none;
        background: rgba(184, 128, 74, 0.92);
        color: #1d120b;
        margin: -16px -16px 12px -16px;
        padding: 10px 12px;
        border-radius: 14px 14px 0 0;
    }

    .experiment-video-card.video-popout .experiment-video-card-titlebar h2 {
        color: #1d120b;
    }

    .experiment-video-card.video-popout #experimentVideoCloseBtn {
        display: inline-flex;
        align-items: center;
        justify-content: center;
    }

    .experiment-video-card.video-popout #experimentVideoPopoutBtn {
        display: none;
    }

    .experiment-video-card.video-popout .experiment-video-frame-wrap {
        aspect-ratio: 16 / 9;
    }

    .experiment-video-card.video-popout.dragging-video {
        opacity: 0.96;
    }

    /* =========================================================
   REACTIVITY POP QUIZ
   ========================================================= */

.reactivity-quiz-layout {
    padding: 18px;

    /* keeps the whole quiz centered instead of touching the right edge */
    width: min(1320px, calc(100vw - 72px));
    max-width: none;
    margin: 0 auto;
}

/* 
   Layout:
   header | buttons | tray
   video  | atoms   | tray
*/
.reactivity-content-grid {
    display: grid;
    grid-template-columns:
        minmax(400px, 560px)
        minmax(470px, 620px)
        150px;
    grid-template-rows: auto minmax(0, 1fr);
    grid-template-areas:
        "header actions tray"
        "video  atoms   tray";
    gap: 18px;
    align-items: stretch;
    justify-content: center;
    min-height: min(720px, calc(100vh - 132px));
}

.reactivity-quiz-header {
    grid-area: header;
    padding: 4px 0 8px;
}

.reactivity-quiz-header h1 {
    margin: 0 0 6px;
    color: #ffffff;
}

.reactivity-quiz-header p {
    margin: 0;
    color: rgb(255, 235, 210);
    max-width: 900px;
}

.reactivity-quiz-actions {
    grid-area: actions;
    align-self: end;
    justify-self: end;

    width: 330px;
    max-width: 100%;

    display: flex;
    gap: 8px;
    padding: 8px;
    border-radius: 16px;
    background: rgba(20, 16, 14, 0.78);
    border: 1px solid rgba(220, 180, 140, 0.28);
}

.reactivity-quiz-actions button {
    flex: 1 1 0;
    min-width: 0;

    background: rgba(84, 68, 56, 0.95);
    color: var(--color-text);
    border: 1px solid rgb(220, 180, 140);
    border-radius: 10px;
    padding: 10px 10px;
    cursor: pointer;
    font-size: 14px;
    font-weight: 700;
    white-space: nowrap;
}

.reactivity-quiz-actions button:hover {
    background: rgb(110, 84, 64);
}

#checkReactivityQuizBtn {
    background: rgb(238, 172, 96);
    color: #1d120b;
}

.reactivity-video-card {
    grid-area: video;

    background: rgba(20, 20, 24, 0.82);
    border: 1px solid rgba(255, 180, 100, 0.25);
    border-radius: 18px;
    padding: 14px;
    min-height: 560px;
}

.reactivity-video-title {
    margin-bottom: 10px;
    color: rgb(255, 210, 160);
    font-weight: 700;
}

.reactivity-video-card iframe {
    width: 100%;
    height: 500px;
    display: block;
    border: 0;
    border-radius: 14px;
    background: #111;
}

.reactivity-atom-area {
    grid-area: atoms;

    position: relative;
    min-height: 600px;
    background:
        radial-gradient(
            circle at 50% 55%,
            rgba(238, 172, 96, 0.16),
            rgba(255, 255, 255, 0.035) 58%,
            rgba(255, 255, 255, 0.015) 100%
        );
    border: 1px solid rgba(255, 255, 255, 0.08);
    border-radius: 32px;
    padding: 14px;
    overflow: hidden;
}

.reactivity-atom-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    gap: 14px;
    margin-bottom: 10px;
}

.reactivity-atom-header h2 {
    margin: 0 0 6px;
    color: #ffffff;
    font-size: 18px;
}

.reactivity-atom-header p,
.reactivity-atom-area p {
    margin: 0;
    color: rgb(214, 202, 190);
    font-size: 13px;
}

.reactivity-atom-pool {
    position: relative;
    min-height: 540px;
    margin-top: 12px;
}

.reactivity-answer-section {
    grid-area: tray;

    position: sticky;
    top: 12px;
    height: min(720px, calc(100vh - 64px));
    min-height: 0;
    background: rgba(15, 15, 18, 0.86);
    border: 1px solid rgba(255, 180, 100, 0.35);
    border-radius: 18px;
    padding: 8px;
    display: flex;
    flex-direction: column;
    overflow: visible;
}

/* Atom buttons */
.reactivity-atom-tile,
.reactivity-answer-tile,
.experiment-reactivity-item {
    width: 58px;
    height: 58px;
    border-radius: 50%;
    border: 2px solid rgba(255, 210, 150, 0.75);
    background: radial-gradient(circle at 35% 30%, rgba(255, 230, 180, 0.95), rgba(210, 115, 45, 0.95));
    color: #1d1208;
    font-weight: 800;
    font-size: 18px;
    cursor: grab;
    box-shadow: 0 8px 18px rgba(0, 0, 0, 0.28);
}

.reactivity-atom-tile {
    position: absolute;
    left: 0;
    top: 0;
    will-change: transform;
    transition: box-shadow 0.15s ease;
}

.reactivity-atom-tile:active,
.reactivity-answer-tile:active {
    cursor: grabbing;
}

/* Stops double-tap zoom so the dblclick-to-remove works on touch */
.reactivity-atom-tile,
.reactivity-answer-slot,
.reactivity-answer-tile {
    touch-action: manipulation;
}

.reactivity-answer-labels.vertical {
    text-align: center;
    color: rgb(255, 210, 160);
    font-weight: 700;
    font-size: 12px;
    margin-bottom: 6px;
}

.reactivity-answer-labels.vertical.bottom {
    margin-top: 6px;
    margin-bottom: 0;
}

.reactivity-answer-tray.vertical {
    flex: 1;
    min-height: 0;
    border: 2px dashed rgba(255, 190, 120, 0.45);
    border-radius: 14px;
    padding: 7px 4px;

    display: flex;
    flex-direction: column;
    gap: var(--tray-gap, 5px);
    align-items: stretch;

    overflow-y: auto;
    overflow-x: hidden;
    scrollbar-gutter: stable both-edges;
    scrollbar-width: thin;
    scrollbar-color: rgba(238, 172, 96, 0.75) rgba(24, 18, 14, 0.9);

    background: rgba(255, 255, 255, 0.03);
}

.reactivity-answer-tray.vertical::-webkit-scrollbar,
.site-sidebar::-webkit-scrollbar,
html::-webkit-scrollbar {
    width: 9px;
}

.reactivity-answer-tray.vertical::-webkit-scrollbar-track,
.site-sidebar::-webkit-scrollbar-track,
html::-webkit-scrollbar-track {
    background: rgba(24, 18, 14, 0.9);
    border-radius: 999px;
}

/* Scrollbar thumb */
.reactivity-answer-tray.vertical::-webkit-scrollbar-thumb,
.site-sidebar::-webkit-scrollbar-thumb,
html::-webkit-scrollbar-thumb {
    background: linear-gradient(
        to bottom,
        rgba(255, 210, 150, 0.95),
        rgba(184, 128, 74, 0.95)
    );
    border-radius: 999px;
    border: 2px solid rgba(24, 18, 14, 0.9);
}

/* Scrollbar hover */
.reactivity-answer-tray.vertical::-webkit-scrollbar-thumb:hover,
.site-sidebar::-webkit-scrollbar-thumb:hover,
html::-webkit-scrollbar-thumb:hover {
    background: linear-gradient(
        to bottom,
        rgba(255, 230, 180, 1),
        rgba(238, 172, 96, 1)
    );
}

.reactivity-mnemonic-tab {
    position: absolute;
    left: -22px;
    top: 48%;
    transform: translateY(-50%);
    z-index: 20;

    width: 24px;
    height: 108px;
    border: 1px solid rgba(255, 190, 120, 0.5);
    border-right: none;
    border-radius: 14px 0 0 14px;

    background: linear-gradient(
        to bottom,
        rgba(238, 172, 96, 0.96),
        rgba(184, 88, 36, 0.96)
    );
    color: #1d1208;
    font-weight: 900;
    font-size: 16px;
    cursor: pointer;

    box-shadow: 0 10px 24px rgba(0, 0, 0, 0.35);
}

.reactivity-mnemonic-tab:hover,
.reactivity-mnemonic-tab.active {
    background: linear-gradient(
        to bottom,
        rgba(255, 220, 165, 1),
        rgba(238, 172, 96, 1)
    );
}

.reactivity-mnemonic-bubble {
    position: absolute;
    right: calc(100% + 40px);
    top: 48%;
    transform: translateY(-50%);
    z-index: 60;

    width: 140px;
    padding: 14px;
    border-radius: 18px;
    border: 1px solid rgba(255, 190, 120, 0.5);

    background:
        radial-gradient(circle at 20% 15%, rgba(238, 172, 96, 0.18), transparent 45%),
        rgba(20, 16, 14, 0.96);
    color: var(--color-text);
    box-shadow: 0 16px 36px rgba(0, 0, 0, 0.45);
}

.reactivity-mnemonic-bubble.hidden {
    display: none;
}

.reactivity-mnemonic-bubble::after {
    content: "";
    position: absolute;
    right: -9px;
    top: 50%;
    transform: translateY(-50%) rotate(45deg);

    width: 16px;
    height: 16px;
    background: rgba(20, 16, 14, 0.96);
    border-top: 1px solid rgba(255, 190, 120, 0.5);
    border-right: 1px solid rgba(255, 190, 120, 0.5);
}

.mnemonic-bubble-title {
    margin-bottom: 8px;
    color: rgb(255, 210, 160);
    font-weight: 800;
    font-size: 14px;
}

.mnemonic-chat-line {
    color: rgb(245, 230, 210);
    font-size: 13px;
    line-height: 1.45;
}

.mnemonic-symbol-row {
    display: flex;
    flex-wrap: wrap;
    gap: 5px;
    margin-top: 10px;
}

.mnemonic-symbol-row span {
    min-width: 28px;
    padding: 4px 6px;
    border-radius: 999px;
    background: rgba(238, 172, 96, 0.16);
    border: 1px solid rgba(255, 190, 120, 0.35);
    color: rgb(255, 220, 175);
    font-size: 12px;
    font-weight: 800;
    text-align: center;
}

.reactivity-answer-tile {
    flex: 0 0 auto;

    width: var(--tray-atom-size, 58px);
    height: var(--tray-atom-size, 58px);
    font-size: var(--tray-atom-font-size, 18px);
    line-height: 1;

    display: inline-flex;
    align-items: center;
    justify-content: center;
    text-align: center;


    transition:
        width 0.18s ease,
        height 0.18s ease,
        font-size 0.18s ease,
        transform 0.18s ease;
}

.reactivity-quiz-feedback {
    margin: 0 0 7px;
    color: rgb(214, 202, 190);
    font-size: 12px;
    line-height: 1.25;
    text-align: center;
}

.reactivity-quiz-feedback.correct {
    color: rgb(125, 235, 160);
}

.reactivity-quiz-feedback.wrong {
    color: rgb(255, 145, 120);
}

.reactivity-quiz-feedback.warning {
    color: rgb(255, 215, 120);
}

.reactivity-answer-tile.tray-float-up {
    animation: trayFloatUp 0.45s ease-out;
}

.reactivity-answer-slot {
    position: relative;
    width: 100%;
    min-height: calc(var(--tray-atom-size, 42px) + 20px);
    padding: 6px 0 14px;
    border: none;
    border-radius: 0;
    background: transparent;

    display: grid;
    place-items: center;
    text-align: center;

    cursor: pointer;
}

.reactivity-answer-slot:hover,
.reactivity-answer-slot.slot-drag-over {
    background: rgba(238, 172, 96, 0.16);
    border-color: rgba(238, 172, 96, 0.95);
}

.reactivity-answer-slot::after {
    content: "";
    position: absolute;
    left: 7px;
    right: 7px;
    bottom: 4px;
    border-bottom: 1px solid rgba(255, 210, 160, 0.22);
    pointer-events: none;
    transition: border-color 0.15s ease, box-shadow 0.15s ease;
}

.reactivity-answer-slot:hover::after,
.reactivity-answer-slot.slot-drag-over::after {
    border-bottom-color: rgba(255, 210, 160, 0.7);
    box-shadow: 0 1px 10px rgba(238, 172, 96, 0.18);
}

.reactivity-answer-slot.slot-correct {
    background: rgba(80, 210, 120, 0.14);
}

.reactivity-answer-slot.slot-correct::after {
    border-bottom-color: rgba(125, 235, 160, 0.85);
    box-shadow: 0 1px 12px rgba(80, 210, 120, 0.22);
}

.reactivity-answer-slot .reactivity-answer-tile.answer-correct {
    border-color: rgba(170, 255, 190, 0.95);
    background: radial-gradient(
        circle at 35% 30%,
        rgba(225, 255, 220, 0.98),
        rgba(74, 198, 112, 0.96)
    );
    color: #102414;
    box-shadow:
        0 0 0 4px rgba(80, 210, 120, 0.22),
        0 8px 18px rgba(0, 0, 0, 0.28);
}

.reactivity-answer-slot .reactivity-answer-tile {
    position: relative;
    z-index: 1;
    cursor: grab;
    margin: 0;
}

.reactivity-atom-tile.selected-floating-atom {
    outline: 3px solid rgba(255, 245, 190, 0.95);
    box-shadow:
        0 0 0 5px rgba(238, 172, 96, 0.22),
        0 10px 24px rgba(0, 0, 0, 0.35);
}

@keyframes trayFloatUp {
    0% {
        transform: translateY(90px) scale(0.92);
        opacity: 0.35;
    }

    65% {
        transform: translateY(-8px) scale(1.04);
        opacity: 1;
    }

    100% {
        transform: translateY(0) scale(1);
        opacity: 1;
    }
}

@media (max-width: 1200px) {
    .reactivity-quiz-layout {
        width: 100%;
        margin: 0;
        transform: none;
    }

    .reactivity-content-grid {
        grid-template-columns: minmax(0, 1fr);
        grid-template-areas:
            "header"
            "video"
            "atoms"
            "tray"
            "actions";
        min-height: auto;
    }

    .reactivity-quiz-actions {
        width: 100%;
        justify-self: stretch;
        align-self: stretch;
    }

    .reactivity-video-card,
    .reactivity-atom-area,
    .reactivity-answer-section {
        position: static;
        height: auto;
        min-height: auto;
    }

    /* Anchor for the mnemonic tab and bubble */
    .reactivity-answer-section {
        position: relative;
    }

    /* Keep feedback text clear of the mnemonic tab */
    .reactivity-quiz-feedback {
        padding: 0 40px;
        min-height: 30px;
    }

    .reactivity-video-card iframe {
        height: auto;
        aspect-ratio: 16 / 9;
    }

    .reactivity-atom-pool {
        min-height: 420px;
    }

    .reactivity-answer-tray.vertical {
        min-height: 120px;
        flex-direction: row;
        overflow-x: auto;
        overflow-y: hidden;
    }

    .reactivity-answer-slot {
        min-width: 48px;
    }

    .reactivity-mnemonic-tab {
        left: auto;
        right: 8px;
        top: 8px;
        transform: none;

        width: 30px;
        height: 32px;
        border-radius: 999px;
        border: 1px solid rgba(255, 190, 120, 0.5);
    }

    .reactivity-mnemonic-bubble {
        right: 8px;
        top: 46px;
        transform: none;
        width: min(280px, calc(100vw - 48px));
    }

    .reactivity-mnemonic-bubble::after {
        display: none;
    }
}

@media (max-width: 600px) {
    .reactivity-quiz-layout {
        padding: 0;
    }

    .reactivity-content-grid {
        gap: 12px;
    }

    .reactivity-quiz-header h1 {
        font-size: clamp(20px, 6vw, 26px);
    }

    .reactivity-quiz-header p {
        font-size: 14px;
    }

    .reactivity-video-card {
        padding: 10px;
        border-radius: 14px;
    }

    .reactivity-atom-area {
        padding: 12px;
        border-radius: 20px;
    }

    .reactivity-atom-pool {
        min-height: 360px;
    }

    /* Wrapping numbered grid instead of a sideways-scrolling row */
    .reactivity-answer-tray.vertical {
        display: grid;
        grid-template-columns: repeat(auto-fill, minmax(56px, 1fr));
        min-height: auto;
        overflow: visible;
        counter-reset: slot;
    }

    .reactivity-answer-slot {
        min-width: 0;
        counter-increment: slot;
    }

    .reactivity-answer-slot::before {
        content: counter(slot);
        position: absolute;
        top: 2px;
        left: 4px;
        font-size: 10px;
        color: rgb(255, 210, 160);
        opacity: 0.6;
        pointer-events: none;
    }

    .reactivity-answer-labels.vertical {
        text-align: left;
    }

    .reactivity-answer-labels.vertical.bottom {
        text-align: right;
    }

    .reactivity-quiz-actions button {
        min-height: 44px;
        font-size: 15px;
    }

    .reactivity-mnemonic-bubble {
        width: min(260px, calc(100vw - 40px));
        max-height: 60vh;
        overflow: auto;
    }
}

#experimentLabLayout {
    position: relative;
}

#experimentReactivityRailCard {
    --experiment-reactivity-slot-height: 54px;
    --experiment-reactivity-atom-size: 42px;
    position: fixed;
    top: 92px;
    right: 24px;
    width: 150px;
    height: calc(100vh - 190px);
    z-index: 2500;
    overflow: hidden;
    text-align: center;

    display: flex;
    flex-direction: column;
}

#experimentReactivityRailCard .experiment-reactivity-scale {
    flex: 1 1 auto;
    display: flex;
    flex-direction: column;
    min-height: 0;
}

#experimentReactivityRailCard .experiment-reactivity-rail {
    flex: 1 1 auto;
    min-height: 0;
    overflow-y: auto;
    overflow-x: hidden;
    padding: 6px 4px;

    display: flex;
    flex-direction: column;
    align-items: stretch;
    gap: 4px;
}


#experimentReactivityRailCard .experiment-reactivity-scale > span {
    text-align: center;
    font-weight: 400;
}

#experimentReactivityRailCard .experiment-reactivity-slot {
    position: relative;
    flex: 0 0 var(--experiment-reactivity-slot-height);
    min-height: var(--experiment-reactivity-slot-height);

    display: grid;
    place-items: center;
}

#experimentReactivityRailCard .experiment-reactivity-slot.empty-slot {
    flex-basis: 18px;
    min-height: 18px;
}

#experimentReactivityRailCard .experiment-reactivity-slot::after {
    content: "";
    position: absolute;
    left: 14px;
    right: 14px;
    bottom: 4px;
    border-bottom: 1px solid rgba(255, 210, 160, 0.22);
}

#experimentReactivityRailCard .experiment-reactivity-slot.empty-slot::after {
    bottom: 2px;
}

#experimentReactivityRailCard .experiment-reactivity-item {
    width: var(--experiment-reactivity-atom-size);
    height: var(--experiment-reactivity-atom-size);
    margin: 0;

    display: grid;
    place-items: center;

    line-height: 1;
    text-align: center;
    font-size: 15px;

    position: relative;
    z-index: 1;
    cursor: default;
}

#experimentReactivityRailCard h2 {
    margin: 0 0 10px;
    font-size: 22px;
    line-height: 1.15;
    text-align: center;
}

#experimentReactivityRailCard .experiment-reactivity-note {
    margin: 0 0 14px;
    font-size: 14px;
    line-height: 1.25;
    text-align: center;
}

#experimentReactivityRailCard .experiment-reactivity-rail {
    scrollbar-width: thin;
    scrollbar-color: rgba(238, 172, 96, 0.75) rgba(24, 18, 14, 0.75);
}

#experimentReactivityRailCard .experiment-reactivity-rail::-webkit-scrollbar {
    width: 6px;
}

#experimentReactivityRailCard .experiment-reactivity-rail::-webkit-scrollbar-track {
    background: rgba(24, 18, 14, 0.75);
    border-radius: 999px;
}

#experimentReactivityRailCard .experiment-reactivity-rail::-webkit-scrollbar-thumb {
    background: linear-gradient(
        to bottom,
        rgba(255, 210, 150, 0.95),
        rgba(184, 128, 74, 0.95)
    );
    border-radius: 999px;
}

#experimentReactivityRailCard .experiment-reactivity-rail::-webkit-scrollbar-thumb:hover {
    background: rgba(255, 220, 165, 1);
}

.element-hover-card {
    position: fixed;
    z-index: 1000;

    width: min(390px, calc(100vw - 24px));
    max-height: min(520px, calc(100vh - 24px));
    overflow-y: auto;

    padding: 14px;

    display: grid;
    grid-template-columns: 64px minmax(0, 1fr);
    gap: 14px;

    color: #f5f5f5;

    background:
        linear-gradient(
            135deg,
            rgba(25, 25, 30, 0.98),
            rgba(55, 30, 15, 0.98)
        );

    border: 1px solid rgba(255, 165, 75, 0.7);
    border-radius: 14px;

    box-shadow:
        0 14px 35px rgba(0, 0, 0, 0.55),
        inset 0 1px 0 rgba(255, 255, 255, 0.05);

    pointer-events: none;

    opacity: 0;
    visibility: hidden;
    transform: translateY(8px);

    transition:
        opacity 140ms ease,
        visibility 140ms ease,
        transform 140ms ease;
}

.element-hover-card.is-active {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

.element-hover-symbol {
    width: 60px;
    height: 60px;

    display: flex;
    align-items: center;
    justify-content: center;

    font-size: 27px;
    font-weight: 800;

    color: #ffffff;
    background: rgba(255, 145, 45, 0.15);
    border: 2px solid rgba(255, 160, 70, 0.65);
    border-radius: 12px;
}

.element-hover-content {
    min-width: 0;
}

.element-hover-heading {
    display: flex;
    align-items: baseline;
    justify-content: space-between;
    gap: 15px;
    margin-bottom: 12px;
}

.element-hover-heading h2 {
    margin: 0;
    font-size: 20px;
    color: #ffb05d;
}

.element-hover-heading > span {
    color: rgba(255, 255, 255, 0.7);
    font-size: 14px;
    white-space: nowrap;
}

.element-hover-properties {
    display: flex;
    flex-wrap: wrap;
    gap: 8px 22px;
    margin-bottom: 15px;
    font-size: 14px;
}

.element-hover-properties strong,
.element-history-section strong {
    color: #ffc98e;
}

.element-history-section {
    border-top: 1px solid rgba(255, 255, 255, 0.12);
    padding-top: 12px;
}

.element-history-section h3 {
    margin: 0 0 7px;
    font-size: 15px;
    color: #ffffff;
}

.element-history-section p {
    margin: 4px 0;
    font-size: 13px;
    line-height: 1.4;
}

.element-history-text {
    font-size: 13px;
    line-height: 1.45;
}

.tile:hover,
.tile:focus-visible {
    z-index: 5;
    transform: translateY(-4px) scale(1.07);
    box-shadow:
        0 10px 22px rgba(0, 0, 0, 0.4),
        0 0 0 2px rgba(255, 255, 255, 0.65);
    outline: none;
}

@media (max-width: 850px) {
    .element-hover-card {
        grid-template-columns: 72px minmax(0, 1fr);
        gap: 14px;
        padding: 14px;
    }

    .element-hover-symbol {
        width: 66px;
        height: 66px;
        font-size: 29px;
    }

    .element-hover-heading {
        align-items: flex-start;
        flex-direction: column;
        gap: 3px;
    }
}




/* Scale label */

.atomic-scale-badge {
    position: absolute;

    top: 12px;
    left: 12px;

    padding: 6px 10px;

    border: 1px solid rgba(238, 172, 96, 0.35);
    border-radius: 999px;

    background: rgba(10, 8, 6, 0.68);

    color: #ffbd78;

    font-size: 11px;
    font-weight: 800;

    letter-spacing: 1.3px;

    pointer-events: none;
}


/* Existing click hint becomes our scale instruction */

.atomic-click-hint {
    position: absolute;

    left: 50%;
    bottom: 7px;

    transform: translateX(-50%);

    width: max-content;
    max-width: 70%;

    text-align: center;

    color: rgba(255, 255, 255, 0.68);

    font-size: 13px;

    pointer-events: none;
}


/* Mixing Lab call-to-action */

.atomic-mixing-guide {
    position: absolute;

    right: 0;

    /*
     * Put it underneath the canvas instead of
     * on top of the lattice/caption.
     */
    bottom: -52px;

    padding: 9px 13px;

    border:
        1px solid
        rgba(238, 172, 96, 0.6);

    border-radius: 10px;

    background:
        rgba(238, 172, 96, 0.12);

    color: #ffd19b;

    font-size: 13px;
    font-weight: 700;

    cursor: pointer;

    z-index: 5;
}


/*
 * Reserve room for the button beneath the viewer.
 */

.atomic-model-stage.is-matter-mode {
    margin-bottom: 58px;
}


.atomic-mixing-guide:hover {
    background:
        rgba(238, 172, 96, 0.24);
}


/* Only disable touch scrolling while the
   interactive matter mode is active. */

.atomic-model-stage.is-matter-mode
#atomicHistoryCanvas {
    touch-action: none;
}


@media (prefers-reduced-motion: reduce) {

    .atomic-model-stage {
        animation: none;
        transform: none;
    }

}

/* =========================================================
   PERIODIC TABLE RESPONSIVE
   ========================================================= */

html,
body {
    width: 100%;
    max-width: 100%;
}


/* =========================================================
   TABLET / SMALL DESKTOP
   ========================================================= */

@media (max-width: 1100px) {

    .page {
        width: 100%;
        max-width: 100%;
    }

    .periodic-table-layout {
        width: 100%;
        min-width: 0;
    }


    /* Viewer above notes */

    .shared-top-layout {
        display: flex;
        flex-direction: column;

        width: 100%;
        min-width: 0;

        gap: 18px;
    }

    .viewer-column {
        width: 100%;
        min-width: 0;
    }

    .viewer-wrap,
    .shared-viewer {
        width: 100%;
        max-width: 100%;
        min-width: 0;
    }

    .shared-side-card,
    #elementInfoCard {
        display: block;

        width: 100%;
        max-width: 100%;
        min-width: 0;
    }


    /* Viewer */

    #atomCanvas {
        display: block;

        width: 100%;
        max-width: 100%;
        height: auto;

        aspect-ratio: 900 / 420;
    }


    /* Buttons */

    .controls {
        display: grid;

        grid-template-columns:
            repeat(3, minmax(0, 1fr));

        gap: 8px;
    }

    .controls button {
        width: 100%;
        min-width: 0;

        white-space: normal;
    }



    /* Periodic table scrolls by itself */

    .table-wrap {
        width: 100%;
        max-width: 100%;

        overflow-x: auto;
        overflow-y: hidden;

        -webkit-overflow-scrolling: touch;
    }
}

/* =========================================================
   PERIODIC TABLE - COMPACT ATOM VIEWER CONTROLS
   ========================================================= */

.viewer-heading-row {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 10px;

    margin-bottom: 10px;
}


.viewer-heading-row .viewer-title {
    margin-bottom: 0;
}


/* Compact viewer controls */

.atom-viewer-controls {
    display: flex;
    align-items: center;
    gap: 7px;

    margin-bottom: 12px;
}

/* =========================================================
   ELEMENT NOTES OPEN / CLOSE
   ========================================================= */

.element-notes-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 12px;

    margin-bottom: 12px;
}


.element-notes-header h2 {
    margin: 0;
}


.notes-close-btn,
.notes-toggle-btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;

    flex: 0 0 auto;

    width: 34px;
    height: 34px;

    padding: 0;

    border:
        1px solid
        rgba(238, 172, 96, 0.55);

    border-radius: 9px;

    background:
        rgba(84, 68, 56, 0.85);

    color: #fff;

    cursor: pointer;

    transition:
        background 0.15s ease,
        border-color 0.15s ease,
        transform 0.15s ease;
}


.notes-close-btn {
    font-size: 23px;
    line-height: 1;
}


.notes-toggle-btn {
    font-size: 16px;
}


.notes-close-btn:hover,
.notes-toggle-btn:hover {
    background:
        rgba(184, 128, 74, 0.95);

    border-color:
        rgb(238, 172, 96);

    transform: translateY(-1px);
}


/* Completely remove the note card when closed */

#elementInfoCard.notes-card-closed {
    display: none !important;
}
/*
   When notes are closed,
   allow the Atom Viewer to use the whole row.
*/
.shared-top-layout.notes-hidden {
    grid-template-columns: minmax(0, 1fr);
}

/* =========================================================
   PHONE
   ========================================================= */

@media (max-width: 600px) {

    .page {
        width: 100%;

        padding:
            10px
            10px
            30px;
    }

    .periodic-table-layout {
        width: 100%;
        min-width: 0;

        padding: 0;
    }


    /* Header */

    .periodic-table-page-header h1 {
        font-size:
            clamp(
                1.8rem,
                8vw,
                2.5rem
            );

        line-height: 1.1;
    }

    .periodic-table-page-header p {
        font-size: 0.92rem;
        line-height: 1.5;
    }


    /* Viewer */

    .viewer-wrap {
        width: 100%;
        min-width: 0;

        padding: 12px;
    }

    .viewer-title {
        font-size: 1.05rem;
    }

    #atomCanvas {
        width: 100%;
        height: auto;

        min-height: 0;
        max-height: none;

        aspect-ratio: 900 / 420;
    }


    /* Compact Atom Viewer controls on mobile only */

    .atom-viewer-controls {
        display: flex;
        flex-direction: row;
        align-items: center;
        gap: 7px;

        margin-bottom: 12px;
    }


    .controls .atom-viewer-icon-btn {
        position: relative;

        width: 38px;
        height: 38px;
        min-height: 38px;

        flex: 0 0 38px;

        padding: 0;

        overflow: hidden;

        border-radius: 9px;

        color: transparent;
        font-size: 0;

        display: inline-flex;
        align-items: center;
        justify-content: center;
    }


    #pauseBtn::before {
        content: "⏯";

        color: #fff;
        font-size: 17px;
        line-height: 1;
    }


    #resetViewBtn::before {
        content: "↺";

        color: #fff;
        font-size: 23px;
        line-height: 1;
    }


    #toggleRenderModeBtn::before {
        content: "☁";

        color: #fff;
        font-size: 18px;
        line-height: 1;
    }


    /* Notes */

    #elementInfoCard {
        width: 100%;

        padding: 14px;

        max-height: none;
        overflow: visible;
    }

    #elementInfoCard h2 {
        font-size: 1.4rem;
    }

    .info-line {
        display: grid;

        grid-template-columns:
            minmax(105px, 0.8fr)
            minmax(0, 1fr);

        gap: 8px;

        align-items: start;
    }

    .info-line span {
        min-width: 0;
        overflow-wrap: anywhere;
    }


    /* Periodic table */

    .table-wrap {
        width: 100%;

        padding: 12px;

        overflow-x: auto;
        overflow-y: hidden;
    }


    /* No hover popup on touchscreen */

    .element-hover-card {
        display: none !important;
    }
}

/* =========================================================
   SHARED SITE NAVIGATION
   ========================================================= */

:root {
    --site-top-height: 64px;
    --site-sidebar-width: 284px;
}


/* =========================================================
   TOP HEADER
   ========================================================= */

.site-header {
    position: fixed;
    inset: 0 0 auto;
    z-index: 1200;

    height: var(--site-top-height);
    padding: 0 22px;

    display: flex;
    align-items: center;
    gap: 18px;

    background: rgba(11, 9, 8, 0.98);
    border-bottom: 1px solid var(--color-border);
}


.site-nav-toggle {
    flex: 0 0 40px;
    height: 40px;

    border: 1px solid var(--color-border);
    border-radius: 10px;

    background: rgba(238, 172, 96, 0.10);
    color: var(--color-accent);

    font-size: 22px;
    cursor: pointer;
}


.site-brand {
    color: var(--color-accent);

    font-size: 18px;
    font-weight: 800;

    text-decoration: none;
    white-space: nowrap;
}


.site-breadcrumb {
    display: flex;
    align-items: center;
    gap: 9px;

    min-width: 0;

    color: var(--color-text-muted);
    font-size: 13px;
}


.site-header-actions {
    margin-left: auto;

    display: flex;
    align-items: center;
    gap: 12px;
}


.site-home-link {
    color: var(--color-text);

    text-decoration: none;
    white-space: nowrap;
}


.site-header .glossary-top-btn {
    margin-left: 0;
    white-space: nowrap;
}


/* =========================================================
   SIDEBAR
   ========================================================= */

.site-sidebar {
    position: fixed;

    z-index: 1150;

    top: var(--site-top-height);
    bottom: 0;
    left: 0;

    width: var(--site-sidebar-width);

    overflow-y: auto;
    overscroll-behavior: contain;

    padding: 18px 12px 32px;

    background:
        linear-gradient(
            145deg,
            #1d130d,
            #0d0b09 65%
        );

    scrollbar-width: thin;
    scrollbar-color:
        rgba(238, 172, 96, 0.75)
        rgba(24, 18, 14, 0.9);
        
    border-right: 1px solid var(--color-border);

    transition: transform 0.22s ease;
}


/* Desktop collapsed state */

.site-sidebar.is-collapsed {
    transform: translateX(-105%);
}


/* =========================================================
   CURRICULUM SELECTOR
   ========================================================= */

.site-curriculum-switch {
    display: grid;

    grid-template-columns:
        repeat(2, minmax(0, 1fr));

    gap: 5px;

    padding: 5px;
    margin-bottom: 18px;

    border: 1px solid var(--color-border);
    border-radius: 12px;
}


.site-curriculum-switch button {
    border: 0;
    border-radius: 8px;

    padding: 10px 5px;

    background: transparent;
    color: var(--color-text);

    font-weight: 700;
    cursor: pointer;
}


.site-curriculum-switch button[aria-pressed="true"] {
    background: var(--color-accent);
    color: #211409;
}


/* =========================================================
   SIDEBAR ACCORDIONS
   ========================================================= */

.site-sidebar summary {
    list-style: none;
    cursor: pointer;
}

.site-sidebar summary::-webkit-details-marker {
    display: none;
}


.site-nav-panel {
    border-bottom:
        1px solid rgba(220, 180, 140, 0.18);
}


.site-nav-panel > summary {
    display: flex;
    align-items: center;
    gap: 8px;

    padding: 13px 9px;

    color: #fff;
    font-weight: 700;
}


.site-nav-panel > summary:hover,
.site-nav-year > summary:hover,
.site-nav-chapter > summary:hover {
    background: rgba(238, 172, 96, 0.09);
}


.site-nav-hint {
    margin-left: auto;

    color: var(--color-text-muted);

    font-size: 11px;
    font-weight: 400;
}


/* Form 4 / Form 5 / IGCSE */

.site-nav-year > summary {
    margin: 4px 0;
    padding: 10px 12px;

    border-radius: 8px;

    background: rgba(238, 172, 96, 0.10);
    color: var(--color-accent);

    font-weight: 700;
}


/* Individual chapters */

.site-nav-chapter > summary {
    margin-left: 10px;
    padding: 9px 10px;

    border-radius: 8px;

    color: var(--color-text-muted);

    font-size: 13px;
    line-height: 1.4;
}


.site-nav-chapter[open] > summary {
    color: #fff;
    background: rgba(238, 172, 96, 0.12);
}


/* =========================================================
   PAGE LINKS
   ========================================================= */

.site-nav-resources {
    padding: 3px 0 8px 22px;
}


.site-nav-link {
    display: block;

    padding: 9px 12px;

    border-radius: 8px;

    color: var(--color-text-muted);

    text-decoration: none;
    font-size: 13px;
    line-height: 1.4;
}


.site-nav-link:hover,
.site-nav-link.is-active {
    color: #fff;
    background: rgba(238, 172, 96, 0.18);
}


.site-nav-link.is-active {
    border-left: 3px solid var(--color-accent);
}


.site-nav-empty {
    display: block;

    padding: 8px 12px;

    color: #968a80;
    font-size: 12px;
}


.site-nav-links {
    padding: 2px 4px 12px 13px;
}


.site-sidebar [hidden],
.site-nav-backdrop[hidden] {
    display: none !important;
}


/* =========================================================
   MOBILE BACKDROP
   ========================================================= */

.site-nav-backdrop {
    position: fixed;

    inset: var(--site-top-height) 0 0;

    z-index: 1100;

    background: rgba(0, 0, 0, 0.72);
}


/* =========================================================
   SHARED PAGE CONTENT POSITION
   ========================================================= */

/*
 * Your shared header is inside .page.
 * Make room for the sidebar and fixed top bar.
 */

.page:has(> .site-header) {
    width: 100%;
    max-width: none;

    margin: 0;

    padding:
        calc(var(--site-top-height) + 20px)
        24px
        40px
        calc(var(--site-sidebar-width) + 24px);
}


/* Sidebar hidden: return content to full width */

.page:has(> .site-sidebar.is-collapsed) {
    padding-left: 24px;
}


/* Keep main content centred */

.page:has(> .site-header) > main {
    width: 100%;
    max-width: 1320px;
    min-width: 0;

    margin-inline: auto;
}


/* =========================================================
   TABLET AND MOBILE
   ========================================================= */

@media (max-width: 900px) {

    /* HEADER */

    .site-header {
        gap: 10px;
        padding-inline: 12px;
    }

    .site-brand {
        font-size: 16px;
    }

    .site-breadcrumb {
        display: none;
    }

    .site-header-actions {
        gap: 8px;
    }

    .site-home-link {
        display: inline-flex;
        align-items: center;
        justify-content: center;

        padding: 8px 10px;

        border: 1px solid var(--color-border);
        border-radius: 8px;

        color: var(--color-text);
        font-size: 13px;
        text-decoration: none;
        white-space: nowrap;
    }

    .site-header .glossary-top-btn {
        padding: 8px 10px;
        font-size: 12px;
    }


    /* SIDEBAR - HIDDEN BY DEFAULT */

    .site-sidebar {
        width: min(320px, 88vw);

        transform: translateX(-105%);

        box-shadow:
            20px 0 45px rgba(0, 0, 0, 0.45);
    }


    /* SIDEBAR - OPEN */

    .site-sidebar.is-open {
        transform: translateX(0);
    }


    /* PAGE LAYOUT */

    .page:has(> .site-header),
    .page:has(> .site-sidebar.is-collapsed) {
        padding:
            calc(var(--site-top-height) + 16px)
            14px
            30px;
    }


    /* PREVENT BACKGROUND SCROLLING */

    body.site-nav-lock {
        overflow: hidden;
    }

}


/* Smaller phones */

@media (max-width: 420px) {

    .site-home-link {
        padding: 8px;
        font-size: 12px;
    }

    .site-brand span {
        display: none;
    }

    .site-brand {
        font-size: 14px;
    }

    .site-header {
        gap: 7px;
    }

    .site-header .glossary-top-btn {
        font-size: 0;
    }

    .site-header .glossary-top-btn::before {
        content: "📖";
        font-size: 18px;
    }

}


@media (prefers-reduced-motion: reduce) {

    .site-sidebar {
        transition: none;
    }

}


/* =========================================================
   APPEARANCE SWITCH / LIGHT THEME
   Scoped overrides also cover the standalone feature styles.
   ========================================================= */

.site-theme-toggle {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    min-height: 40px;
    padding: 8px 11px;
    border: 1px solid var(--color-border);
    border-radius: 10px;
    background: rgba(238, 172, 96, 0.10);
    color: var(--color-text);
    font: inherit;
    font-size: 13px;
    white-space: nowrap;
    cursor: pointer;
}

.site-theme-toggle:hover {
    border-color: var(--color-accent);
    background: rgba(238, 172, 96, 0.18);
}

.site-theme-toggle:focus-visible {
    outline: 3px solid var(--color-accent);
    outline-offset: 3px;
}

.site-theme-toggle svg {
    flex-shrink: 0;
    color: var(--color-accent);
}

.site-theme-track {
    position: relative;
    flex: 0 0 28px;
    width: 28px;
    height: 16px;
    border-radius: 999px;
    background: var(--color-text-muted);
}

.site-theme-track::before {
    content: "";
    position: absolute;
    inset: 3px auto auto 3px;
    width: 10px;
    height: 10px;
    border-radius: 50%;
    background: var(--color-bg-dark);
}

.site-theme-toggle[aria-pressed="true"] {
    border-color: var(--color-accent);
    background: var(--theme-hover);
}

.site-theme-toggle[aria-pressed="true"] .site-theme-track {
    background: var(--color-accent);
}

.site-theme-toggle[aria-pressed="true"] .site-theme-track::before {
    transform: translateX(12px);
}

@media (max-width: 1100px) {
    .site-breadcrumb {
        display: none;
    }
}

@media (max-width: 600px) {
    .site-brand span {
        display: none;
    }

    .site-theme-toggle {
        gap: 6px;
        padding: 8px;
        font-size: 12px;
    }
}

@media (max-width: 420px) {
    .site-theme-label,
    .site-theme-track {
        display: none;
    }

    .site-theme-toggle {
        width: 40px;
        flex-shrink: 0;
    }
}

:root[data-theme="light"] {
    color-scheme: light;
    --color-bg-dark: #f8f5f0;
    --color-bg-card: #ffffff;
    --color-bg-panel: #fffaf4;
    --color-text: #30261e;
    --color-text-muted: #65574b;
    --color-accent: #945018;
    --color-accent-dark: #9d6030;
    --color-border: rgba(125, 83, 45, 0.30);
    --card-shadow: 0 12px 36px rgba(83, 54, 29, 0.10);
    --theme-inset: #f3eadf;
    --theme-hover: #eddbc4;
    --theme-success: #25643b;
    --theme-danger: #a53131;
}

:root[data-theme="light"] body {
    background: linear-gradient(to top, #efdbc3, var(--color-bg-dark) 35%);
}

/* Navigation, cards, dialogs and feature panels. */
:root[data-theme="light"] :is(
    .site-header, .site-sidebar, .curriculum-chapter, .table-wrap,
    .glossary-window, .glossary-sidebar, .element-hover-card,
    .mix-help-popup, .question-mini-app,
    .reactivity-quiz-actions, .reactivity-video-card, .reactivity-answer-section,
    .reactivity-mnemonic-bubble,
    .periodic-puzzle-piece-panel, .periodic-puzzle-table-panel,
    .thomson-crt-section, .thomson-crt-controls, .thomson-crt-video-panel,
    .atom-builder-picker-card, .atom-builder-selected-card,
    .atom-builder-electron-card, .atom-builder-progress-card,
    .atom-builder-element-tile, .atom-builder-workspace, .atom-builder-isotope-use-card,
    .nucleus-builder-card,
    .isotope-quiz-score-card, .isotope-quiz-nucleus-card, .isotope-quiz-question,
    .radiation-simulation-card, .radiation-control-card,
    .carbon-mission-panel, .carbon-info-panel, .carbon-quiz-stage,
    .conversion-level-chooser, .conversion-quiz-panel, .guide-progress-item,
    .experiment-floating-panel, .experiment-clock-overlay,
    .reactor-component-panel, .reactor-simulation-section,
    .reactor-type-card, .reactor-glossary-panel,
    .salts-panel, .salts-concept, .salts-why
) {
    background: var(--color-bg-panel);
    border-color: var(--color-border);
    color: var(--color-text);
}

:root[data-theme="light"] :is(
    .mix-bond-type-link, .reactivity-mnemonic-bubble,
    .atom-builder-atomic-number-info, .wire-visual
)::after {
    background: var(--color-bg-panel);
    border-color: var(--color-border);
    color: var(--color-text);
}

:root[data-theme="light"] .site-header {
    background: #fffaf4;
    box-shadow: 0 2px 12px rgba(83, 54, 29, 0.06);
}

:root[data-theme="light"] .site-sidebar {
    background: linear-gradient(145deg, #f5e7d5, #fffaf4 70%);
}

:root[data-theme="light"] :is(
    h1, h2, h3, h4, .curriculum-chapter-title, .atomic-scientist-caption strong,
    .site-nav-panel > summary, .site-nav-chapter[open] > summary,
    .site-nav-link:hover, .site-nav-link.is-active,
    .glossary-close-btn, .glossary-term-btn, .glossary-example,
    .reactor-glossary-header button,
    .element-hover-symbol, .notes-close-btn, .notes-toggle-btn,
    .periodic-puzzle-panel-title, .periodic-puzzle-piece, .periodic-puzzle-element,
    .thomson-crt-video-header strong, .atom-builder-element-choice,
    .atom-builder-symbol, .atom-builder-composition strong,
    .atom-builder-configuration-value, .atom-builder-charge-equation,
    .atom-builder-isotope-concept strong, .atom-builder-use-isotope,
    .atom-builder-isotope-safety-note strong,
    .nucleus-builder-control-heading strong, .nucleus-builder-equation strong,
    .nucleus-builder-notation, .nucleus-builder-element-symbol,
    .nucleus-builder-result-data strong, .nucleus-builder-periodic-cell,
    .nucleus-builder-periodic-cell strong,
    .nucleus-builder-periodic-cell small, .nucleus-builder-decay-stats strong,
    .nucleus-builder-isotope-history-note strong,
    .isotope-quiz-notation, .isotope-quiz-counts strong,
    .isotope-quiz-change-item strong, .isotope-quiz-guide-item span,
    .isotope-quiz-feedback-changes b, .isotope-quiz-answers button,
    .radiation-plate-status strong, .radiation-type-buttons button,
    .radiation-prediction-buttons button, .carbon-quiz-layout,
    .carbon-electron-config strong, .carbon-answer-btn,
    .carbon-discovery-unlocked > strong, .carbon-connect-atom,
    .carbon-structure-progress span.active, .carbon-final-term,
    .experiment-field label, .energy-flow-item strong,
    .component-text strong, .sim-control-heading strong,
    .sim-switch-row strong, .sim-readout strong, .reactor-type-name,
    .reactor-comparison-table tbody th
) {
    color: var(--color-text);
}

:root[data-theme="light"] #periodicPuzzleProgress {
    color: var(--color-text);
}

:root[data-theme="light"] :is(
    .atomic-model-history-copy > p, .atomic-model-evidence p,
    .atomic-scientist-caption span, .curriculum-no-feature, .site-nav-empty,
    .glossary-explanation p, .glossary-section li, .element-hover-heading > span,
    .curve-dropdown summary small, .energy-curve-note, .energy-slider-row,
    .experiment-step, .experiment-current-tool, .experiment-video-header span,
    .experiment-video-note, .reactivity-quiz-header p, .reactivity-atom-header p,
    .reactivity-atom-area p, .reactivity-quiz-feedback, .mnemonic-chat-line,
    .periodic-puzzle-small-text, .periodic-puzzle-piece span,
    .periodic-puzzle-slot-hint, .periodic-puzzle-transition-note,
    .periodic-puzzle-element-number, .periodic-puzzle-status,
    .rutherford-result span, .thomson-crt-heading p, .thomson-crt-control label,
    .thomson-crt-observation p, .thomson-crt-conclusion p,
    .thomson-crt-video-header span, .atom-builder-electron-card small,
    .atom-builder-isotope-graphic > span,
    .carbon-quiz-header p, .carbon-discovery-unlocked p, .carbon-mission-progress,
    .carbon-electron-config, .carbon-element-tile .carbon-number,
    .carbon-element-tile > span:last-child, .carbon-chain-bond,
    .carbon-challenge-header p, .carbon-structure-progress span,
    .carbon-isomer-card > span, .carbon-allotrope-card span,
    .experiment-reaction-time, .experiment-input-with-unit span,
    .energy-flow-item span, .energy-arrow, .component-number,
    .component-text small, .component-arrow, .process-number, .process-connector,
    .reactor-component-info > p, .reactor-info-fact span,
    .sim-control-row label, .sim-control-row > span, .sim-control-scale,
    .sim-switch-row span, .sim-readout > span, .sim-readout small,
    .reactor-reset-button, .sim-toggle-button, .sim-speed-buttons button,
    .reactor-glossary-content p,
    .reactor-glossary-content li, .reactor-glossary-content .glossary-example,
    .reactor-glossary-term-list .glossary-term-btn
) {
    color: var(--color-text-muted);
}

:root[data-theme="light"] #atomicModelDescription,
:root[data-theme="light"] #carbonExplanation {
    color: var(--color-text-muted);
}

:root[data-theme="light"] :is(
    .curriculum-chapter-number, .curriculum-feature-btn, .atomic-history-label,
    .atomic-evidence-label, .glossary-header-label, .glossary-category,
    .glossary-link, .glossary-link:hover, .glossary-term-btn.is-selected,
    .glossary-short-definition, .element-hover-properties strong,
    .element-history-section strong, .element-use-name, .compound-use-item span,
    .frequent-compound span, .mix-bond-type-link, .energy-curve-title,
    .energy-curve-subtitle, .curve-dropdown summary, .apparatus-name,
    .question-item strong, .reactivity-video-title, .reactivity-answer-labels.vertical,
    .mnemonic-bubble-title, .mnemonic-symbol-row span,
    .atomic-mixing-guide, .periodic-puzzle-piece strong,
    .periodic-puzzle-transition-note strong, .atom-builder-element-choice.selected,
    .atom-builder-atomic-number-info, .atom-builder-configuration-label,
    .atom-builder-shell-counter, .atom-builder-isotope-field,
    .atom-builder-isotope-description, .nucleus-builder-notation sup,
    .nucleus-builder-notation sub, .nucleus-builder-element-number,
    .nucleus-builder-decay-equation, .isotope-quiz-score-card strong,
    .isotope-quiz-state, .isotope-quiz-energy-change, .isotope-quiz-guide-item strong,
    .isotope-quiz-emission, .isotope-quiz-answers button strong,
    .carbon-quiz-eyebrow, .carbon-mission-label, .carbon-discovery-unlocked > span,
    .carbon-allotrope-symbol, .carbon-final-chain > span, .carbon-final-result strong,
    .conversion-node-icon, .conversion-node-action, .conversion-level-intro strong,
    .conversion-level-btn span, .level2-route-btn strong, .map-connector,
    .map-arrow-label, .map-connector-vertical > span:first-child,
    .map-connector-vertical > span:last-child, .conversion-quiz-topic,
    .conversion-score, .guide-progress-item.active, .guide-step-label,
    .operation-symbol, .factor-working-row strong, .factor-reference-box,
    .conversion-answer-field span, .conversion-equation-display,
    .conversion-final-score, .question-atomic-reference, .mass-guided-symbol,
    .mass-guided-times, .mass-guided-inline-plus, .guided-operation-btn span,
    .question-mol-link, .experiment-clock-label, .experiment-clock-time,
    .experiment-reactivity-close-btn, .reactor-status-pill, .reactor-fission-open,
    .reactor-component-button.active .component-number, .reactor-info-eyebrow,
    .reactor-info-fact strong, .sim-control-row output, .sim-speed-buttons button.active,
    .reactor-type-facts span, .reactor-glossary-sidebar label,
    .reactor-glossary-content h4,
    .reactor-glossary-term-list .glossary-term-btn.is-selected
) {
    color: var(--color-accent);
}

:root[data-theme="light"] :is(.reactivity-answer-slot, .periodic-puzzle-slot)::before {
    color: var(--color-accent);
}

:root[data-theme="light"] #atomicModelName,
:root[data-theme="light"] #carbonQuizScore,
:root[data-theme="light"] #carbonStructureChallengeNumber,
:root[data-theme="light"] #conversionQuestionNumber,
:root[data-theme="light"] #mixResult,
:root[data-theme="light"] #mixFormula,
:root[data-theme="light"] #mixType,
:root[data-theme="light"] #mixBondStrength,
:root[data-theme="light"] #mixBondForce,
:root[data-theme="light"] #mixStability,
:root[data-theme="light"] #mixTemperatureValue,
:root[data-theme="light"] #experimentVoltageValue,
:root[data-theme="light"] #experimentCathodeEquation,
:root[data-theme="light"] #experimentAnodeEquation,
:root[data-theme="light"] #titrationEquation {
    color: var(--color-accent);
}

:root[data-theme="light"] .reactor-glossary-content #glossaryCategory {
    color: var(--color-accent);
}

:root[data-theme="light"] .salts-beaker-formula {
    color: #345963;
}

:root[data-theme="light"] .salts-beaker::before {
    background: var(--color-bg-panel);
    border-color: rgba(75, 108, 124, 0.45);
}

:root[data-theme="light"] #mixInfoCard .info-label,
:root[data-theme="light"] .vertical-arrow,
:root[data-theme="light"] .fission-lesson-controls button {
    color: var(--color-text);
}

:root[data-theme="light"] .fission-lesson-controls .fission-play-btn {
    background: var(--color-accent);
    color: #fff;
}

:root[data-theme="light"] .tile:not(.block-unknown) {
    color: #30261e;
}

/* Inputs and neutral buttons retain their existing layout and interaction. */
:root[data-theme="light"] :is(
    .app-button, .standard-button, .controls button, .tab-btn,
    .experiment-run-controls button, .experiment-setup-card button,
    .experiment-tool, .experiment-video-actions button,
    .reactivity-quiz-actions button, .glossary-top-btn, .glossary-search,
    .glossary-close-btn, .notes-close-btn, .notes-toggle-btn,
    .question-answer, .curve-dropdown, .energy-curve-box,
    .thomson-crt-control select, .atom-builder-element-choice,
    .nucleus-builder-stepper button, .nucleus-builder-stepper input,
    .isotope-quiz-notation, .isotope-quiz-answers button,
    .radiation-type-buttons button, .radiation-prediction-buttons button,
    .carbon-answer-btn, .carbon-builder-workspace,
    .calculation-secondary-btn, .conversion-node,
    .conversion-level-btn, .level2-route-btn, .conversion-close-btn,
    .quantity-choice-btn, .conversion-answer-field, .mass-guided-input,
    .guided-operation-btn, .experiment-floating-panel select,
    .titration-controls input[type="number"], .experiment-reactivity-close-btn,
    .reactor-glossary-sidebar input
) {
    background: var(--theme-inset);
    border-color: var(--color-border);
    color: var(--color-text);
}

:root[data-theme="light"] #atomBuilderGroupSelect,
:root[data-theme="light"] #atomBuilderIsotopeSelect,
:root[data-theme="light"] #electrolysisCard select,
:root[data-theme="light"] #experimentLabCard select,
:root[data-theme="light"] #resetTemperatureBtn,
:root[data-theme="light"] #resetEnergyCurveBtn {
    background: var(--theme-inset);
    border-color: var(--color-border);
    color: var(--color-text);
}

:root[data-theme="light"] :is(
    .app-button, .standard-button, .controls button, .tab-btn,
    .experiment-tool, .experiment-video-actions button,
    .reactivity-quiz-actions button, .glossary-top-btn,
    .notes-close-btn, .notes-toggle-btn, .atom-builder-element-choice,
    .nucleus-builder-stepper button, .isotope-quiz-answers button,
    .carbon-answer-btn, .calculation-secondary-btn, .conversion-node,
    .conversion-level-btn, .level2-route-btn, .quantity-choice-btn,
    .guided-operation-btn
):hover:not(:disabled) {
    background: var(--theme-hover);
    border-color: var(--color-accent);
}

:root[data-theme="light"] :is(
    .site-curriculum-switch button[aria-pressed="true"],
    .calculation-primary-btn, .salts-button-primary, .periodic-puzzle-continue,
    .experiment-tool.active, .tab-btn.active, .guide-step-number
) {
    background: var(--color-accent);
    color: #fff;
}

:root[data-theme="light"] :is(
    .atom-builder-element-choice.selected, button.conversion-node.selected,
    .conversion-level-btn.active, .level2-route-btn.active,
    .quantity-choice-btn.selected, .isotope-quiz-answers button.selected,
    .radiation-type-buttons button.active, .radiation-prediction-buttons button.selected
) {
    background: var(--theme-hover);
    color: var(--color-accent);
    border-color: var(--color-accent);
}

:root[data-theme="light"] :is(
    .periodic-puzzle-slot, .periodic-puzzle-transition-note,
    .carbon-mission-progress, .carbon-builder-workspace, .glossary-sidebar,
    .glossary-header, .glossary-search, .glossary-example, .element-history-section
) {
    border-color: var(--color-border);
}

/* Feedback colors need stronger contrast against the pale surfaces. */
:root[data-theme="light"] :is(
    .reactivity-quiz-feedback.correct, .nucleus-builder-stability.stable,
    .radiation-deflection-feedback.correct, .thomson-crt-observation strong,
    .carbon-answer-btn.correct-answer, .carbon-answer-btn.correct-answer:disabled,
    .carbon-structure-progress span.complete,
    .mass-guided-input.is-correct, .guided-operation-btn.is-correct,
    .guided-operation-feedback.correct, .sim-toggle-button.active, .reactor-start-button
) {
    color: var(--theme-success);
}

:root[data-theme="light"] .carbon-answer-btn.correct-answer::after {
    color: var(--theme-success);
}

:root[data-theme="light"] #mixDistanceValue {
    color: var(--theme-success);
}

:root[data-theme="light"] :is(
    .reactivity-quiz-feedback.wrong, .nucleus-builder-stability.unstable,
    .guided-operation-feedback.incorrect, .reactor-scram-button,
    .reactor-sim-warning, .simulation-state-pill.warning
) {
    color: var(--theme-danger);
}

:root[data-theme="light"] :is(
    .reactivity-quiz-feedback.warning, .nucleus-builder-stability.particle-unstable,
    .radiation-deflection-feedback.incorrect
) {
    color: var(--color-accent);
}

:root[data-theme="light"] .salts-page {
    --salts-muted: var(--color-text-muted);
    --salts-border: var(--color-border);
    --salts-red: #a52d46;
    --salts-blue: #3457a6;
    --salts-green: #25643b;
}

:root[data-theme="light"] .reactor-page {
    --reactor-orange: #a65016;
    --reactor-orange-bright: #945018;
    --reactor-blue: #14628e;
    --reactor-panel: var(--color-bg-panel);
    --reactor-border: var(--color-border);
    --reactor-muted: var(--color-text-muted);
}

:root[data-theme="light"] #pauseBtn::before,
:root[data-theme="light"] #resetViewBtn::before,
:root[data-theme="light"] #toggleRenderModeBtn::before {
    color: var(--color-text);
}

/* Home and periodic-table renderers supply a matching light drawing palette. */
:root[data-theme="light"] :is(
    .atomic-model-stage, .rutherford-foil-viewer, .thomson-crt-viewer,
    .experiment-workspace, .experiment-main-viewer
) {
    background: var(--color-bg-panel);
    color: var(--color-text);
    border-color: var(--color-border);
}

:root[data-theme="light"] #periodicTableLayout {
    --viewer-theme: light;
}

:root[data-theme="light"] #periodicTableLayout #atomCanvas,
:root[data-theme="light"] #experimentLabCanvas {
    background: var(--color-bg-panel);
}

:root[data-theme="light"] :is(
    .atomic-click-hint, .thomson-crt-visual-note, .thomson-crt-drag-hint
) {
    color: var(--color-text-muted);
}

:root[data-theme="light"] .atomic-scale-badge {
    background: var(--theme-inset);
    color: var(--color-accent);
}

:root[data-theme="light"] .atomic-progress-dot:not(.is-active) {
    background: var(--color-border);
}

:root[data-theme="light"] .experiment-workspace :is(
    .gas-tube-visual, .bottle-body, .bottle-neck, .indicator-visual
),
:root[data-theme="light"] .experiment-workspace :is(
    .beaker-visual, .conical-flask-visual, .pipette-visual, .burette-visual
)::before,
:root[data-theme="light"] .experiment-workspace :is(
    .conical-flask-visual, .pipette-visual
)::after {
    border-color: #4b6c7c;
}

:root[data-theme="light"] .experiment-workspace .pipette-visual::before {
    background: #4b6c7c;
}

:root[data-theme="light"] :is(.experiment-floating-panel, .experiment-clock-overlay) {
    box-shadow: var(--card-shadow);
}

/* The remaining scientific viewers retain their existing drawing palettes. */
:root[data-theme="light"] :is(
    .radiation-svg-wrap, .reactor-diagram-card, .reactor-plant-card, .fission-visual
) {
    background: #151310;
    color: #f5f0eb;
    --color-text: #f5f0eb;
    --color-text-muted: #d6cabe;
    --color-accent: #eeac60;
    --reactor-orange: #ff8a2a;
    --reactor-orange-bright: #ffb14a;
    --reactor-blue: #27b8ff;
    --reactor-muted: rgba(255, 255, 255, 0.72);
}

:root[data-theme="light"] #atomCanvas,
:root[data-theme="light"] #electrolysisCanvas,
:root[data-theme="light"] #mixEnergyCurve,
:root[data-theme="light"] #mixTemperatureCurve {
    background-color: #151310;
}

:root[data-theme="light"] .site-sidebar,
:root[data-theme="light"] {
    scrollbar-color: #a56b36 #f3eadf;
}

:root[data-theme="light"] .site-sidebar::-webkit-scrollbar-track,
:root[data-theme="light"]::-webkit-scrollbar-track {
    background: var(--theme-inset);
}

:root[data-theme="light"] .site-sidebar::-webkit-scrollbar-thumb,
:root[data-theme="light"]::-webkit-scrollbar-thumb {
    background: #a56b36;
    border-color: var(--theme-inset);
}