/* === Reset === */
*, *::before, *::after {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

/* === Graph-paper design tokens === */
:root {
    --paper: #ece5d2;
    --paper-deep: #e5dcc5;
    --card: #f4efe2;
    --ink: #2d2d2a;
    --ink-soft: #4c4c47;
    --grid: #848fa5;
    --accent: #c14953;
    --accent-dark: #892f35;
    --font-display: 'Atma', system-ui, sans-serif;
    --font-mono: 'IBM Plex Mono', ui-monospace, SFMono-Regular, Consolas, monospace;
    --rule: 1px solid var(--ink);
    --shadow-hard: 4px 4px 0 var(--ink);

    /* Canvas drawing palette. SimLib.Theme reads these at startup, so this
       block is the single source for simulation scenes as well as the page. */
    --muted: #5e5d57;
    --faint: #8f8d84;
    --secondary: #5b6b8c;
    --secondary-soft: #dfe2e8;
    --glow: #e8b23a;
    --canvas-bg: var(--card);
    --canvas-surface: #faf7ef;
    --canvas-grid: #dcd9d0;
    --canvas-grid-strong: #c3c5c8;
    --canvas-border: #cfc6ae;
    --series-1: var(--accent);
    --series-2: var(--secondary);
    --series-3: #b07a1a;
    --series-4: var(--ink);
    --series-5: var(--sim-success);

    /* Simulation, guided-lesson and CFU components read these. */
    --sim-accent: var(--accent);
    --sim-accent-dark: var(--accent-dark);
    --sim-accent-soft: #f1dcd6;
    --sim-accent-softer: #f5e7e1;
    --sim-ink: var(--ink);
    --sim-text: var(--ink-soft);
    --sim-muted: var(--ink-soft);
    --sim-faint: #6b6a62;
    --sim-border: #bdb49d;
    --sim-border-strong: var(--ink);
    --sim-surface: var(--card);
    --sim-surface-2: var(--paper);
    --sim-bg: var(--paper);
    --sim-radius-sm: 0;
    --sim-radius: 0;
    --sim-radius-lg: 0;
    --sim-shadow: var(--shadow-hard);
    --sim-shadow-sm: none;
    --sim-danger: #a3262f;
    --sim-danger-soft: #f3d6d2;
    --sim-success: #2f6b3a;
    --sim-success-soft: #dde8d2;
    --sim-warn: #8a5300;
    --sim-warn-soft: #f2e2b8;
}

html {
    font-size: 16px;
    scroll-behavior: smooth;
}

body {
    min-height: 100vh;
    font-family: var(--font-display);
    line-height: 1.6;
    color: var(--ink);
    background: var(--paper);
    -webkit-font-smoothing: antialiased;
}

/* Graph paper: 24px minor grid with a 120px major grid. */
.paper {
    background-color: var(--paper);
    background-image:
        linear-gradient(rgba(132, 143, 165, .30) 1px, transparent 1px),
        linear-gradient(90deg, rgba(132, 143, 165, .30) 1px, transparent 1px),
        linear-gradient(rgba(132, 143, 165, .14) 1px, transparent 1px),
        linear-gradient(90deg, rgba(132, 143, 165, .14) 1px, transparent 1px);
    background-size: 120px 120px, 120px 120px, 24px 24px, 24px 24px;
    background-position: -1px -1px;
}

.paper-dark {
    background-color: var(--ink);
    background-image:
        linear-gradient(rgba(229, 220, 197, .07) 1px, transparent 1px),
        linear-gradient(90deg, rgba(229, 220, 197, .07) 1px, transparent 1px);
    background-size: 24px 24px;
}

img {
    max-width: 100%;
    display: block;
}

ul {
    list-style: none;
}

a {
    color: inherit;
    text-decoration: none;
}

a:focus-visible,
button:focus-visible,
input:focus-visible,
select:focus-visible {
    outline: 2px solid var(--accent);
    outline-offset: 3px;
}

/* === Layout === */
.container {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 clamp(16px, 4vw, 40px);
}

.section {
    padding: 96px 0;
    border-top: var(--rule);
}

.section-title {
    font-size: clamp(36px, 4.5vw, 52px);
    font-weight: 700;
    line-height: 1.05;
    letter-spacing: -0.01em;
    margin-bottom: 56px;
}

.section-intro {
    font-size: 17px;
    color: var(--ink-soft);
    max-width: 34em;
}

.section-head {
    display: flex;
    flex-wrap: wrap;
    align-items: flex-end;
    justify-content: space-between;
    gap: 24px;
    margin-bottom: 48px;
}

.section-head .section-title {
    margin-bottom: 12px;
}

.text-link {
    color: var(--accent-dark);
    text-decoration: underline;
    font-weight: 500;
    min-height: 44px;
    display: inline-flex;
    align-items: center;
}

.text-link:hover {
    color: var(--ink);
}

/* === Header / Navigation === */
.site-header {
    position: sticky;
    top: 0;
    z-index: 1000;
    background: rgba(236, 229, 210, 0.88);
    backdrop-filter: blur(6px);
    border-bottom: var(--rule);
}

.nav-container {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    justify-content: space-between;
    gap: 16px 32px;
    padding-top: 18px;
    padding-bottom: 18px;
}

.logo {
    display: flex;
    align-items: center;
    gap: 12px;
    font-weight: 700;
    font-size: 24px;
    letter-spacing: -0.02em;
    color: var(--ink);
}

.logo-mark {
    flex-shrink: 0;
}

.site-header nav a {
    color: var(--ink-soft);
    transition: color 0.2s;
}

.site-header nav a:hover,
.primary-nav a.is-active {
    color: var(--accent);
}

.primary-nav ul {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 8px 28px;
}

.primary-nav a {
    font-size: 15px;
}

/* === Buttons === */
.btn {
    display: inline-flex;
    align-items: center;
    gap: 10px;
    min-height: 44px;
    padding: 15px 24px;
    border: var(--rule);
    font: inherit;
    font-size: 16px;
    font-weight: 500;
    line-height: 1.2;
    cursor: pointer;
    transition: background 0.15s, color 0.15s;
}

.btn-sm {
    padding: 10px 16px;
    font-size: 15px;
}

.btn-primary {
    background: var(--accent);
    color: #ffffff;
    font-weight: 600;
    box-shadow: 3px 3px 0 var(--ink);
}

.btn-primary:hover {
    background: var(--accent-dark);
}

.btn-ghost,
.primary-nav .btn-ghost {
    background: transparent;
    color: var(--ink);
}

.btn-ghost:hover,
.primary-nav .btn-ghost:hover {
    background: var(--ink);
    color: var(--paper);
}

.btn-on-dark {
    border-color: var(--paper-deep);
    box-shadow: none;
}

/* === Hero === */
.hero {
    padding: 88px 0 104px;
}

.hero-content {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 56px;
}

.hero-copy {
    flex: 1 1 440px;
    min-width: 0;
    display: flex;
    flex-direction: column;
    gap: 28px;
}

.hero h1 {
    font-size: clamp(44px, 6vw, 72px);
    font-weight: 700;
    line-height: 1;
    letter-spacing: -0.01em;
}

.hero-subtitle {
    font-size: 20px;
    line-height: 1.55;
    color: var(--ink-soft);
    max-width: 34em;
}

.hero-actions {
    display: flex;
    flex-wrap: wrap;
    gap: 14px;
}

.hero-figure {
    flex: 1 1 460px;
    min-width: 0;
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.hero-figure svg {
    display: block;
    width: 100%;
    height: auto;
}

.hero-figure figcaption {
    font-family: var(--font-mono);
    font-size: 13px;
    color: var(--ink-soft);
    border-top: var(--rule);
    padding-top: 10px;
}

/* === Mission === */
.mission-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
    gap: 40px;
}

.mission-item {
    border-top: 2px solid var(--ink);
    padding-top: 20px;
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.mission-item h3 {
    font-size: 24px;
    font-weight: 700;
    letter-spacing: -0.01em;
    line-height: 1.2;
}

.mission-item p {
    font-size: 17px;
    color: var(--ink-soft);
}

/* === Goals List === */
.goals-layout {
    display: flex;
    flex-wrap: wrap;
    gap: 48px 80px;
}

.goals-intro {
    flex: 1 1 280px;
}

.goals-intro .section-title {
    margin-bottom: 20px;
}

.goals-intro .section-intro {
    max-width: 22em;
}

.goals-list {
    flex: 999 1 560px;
    min-width: 0;
    list-style: none;
    border-bottom: var(--rule);
}

.goals-list li {
    display: grid;
    grid-template-columns: 88px minmax(0, 1fr);
    gap: 16px;
    padding: 28px 0;
    border-top: var(--rule);
}

.goal-number {
    font-size: 44px;
    font-weight: 700;
    line-height: 1;
    color: var(--accent);
}

.goal-content {
    display: flex;
    flex-direction: column;
    gap: 6px;
}

.goal-content h3 {
    font-size: 20px;
    font-weight: 600;
    line-height: 1.3;
}

.goal-content p {
    font-size: 17px;
    color: var(--ink-soft);
}

/* === Spec sheet (features) === */
.spec-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 1px;
    background: var(--ink);
    border: var(--rule);
}

.spec-item {
    background: var(--card);
    padding: 32px;
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.spec-icon {
    fill: none;
    stroke: var(--accent);
    stroke-width: 2;
    stroke-linecap: round;
    stroke-linejoin: round;
}

.spec-item h3 {
    font-size: 20px;
    font-weight: 600;
    line-height: 1.3;
}

.spec-item p {
    font-size: 16px;
    color: var(--ink-soft);
}

/* === Simulations Grid === */
.sim-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
    gap: 32px;
}

.sim-card {
    display: flex;
    flex-direction: column;
    background: var(--card);
    border: var(--rule);
    box-shadow: var(--shadow-hard);
    color: var(--ink);
    transition: transform 0.15s, box-shadow 0.15s;
}

.sim-card:hover {
    transform: translate(-2px, -2px);
    box-shadow: 6px 6px 0 var(--ink);
}

.sim-thumb {
    position: relative;
    height: 150px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-bottom: var(--rule);
    background-color: var(--paper-deep);
    background-image:
        linear-gradient(rgba(132, 143, 165, .28) 1px, transparent 1px),
        linear-gradient(90deg, rgba(132, 143, 165, .28) 1px, transparent 1px);
    background-size: 12px 12px;
}

.sim-thumb svg {
    width: 220px;
    height: auto;
}

.sim-fig {
    position: absolute;
    top: 10px;
    left: 12px;
    font-family: var(--font-mono);
    font-size: 12px;
    color: var(--ink-soft);
}

.sim-body {
    display: flex;
    flex-direction: column;
    gap: 12px;
    flex-grow: 1;
    padding: 24px;
}

.sim-meta {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 10px;
}

.sim-name {
    font-size: 26px;
    font-weight: 700;
    line-height: 1.2;
    letter-spacing: -0.015em;
    transition: color 0.15s;
}

.sim-card:hover .sim-name {
    color: var(--accent);
}

.sim-desc {
    font-size: 16px;
    color: var(--ink-soft);
}

.sim-tag {
    display: inline-block;
    align-self: flex-start;
    font-family: var(--font-mono);
    font-size: 12px;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    padding: 4px 8px;
    border: 1px solid var(--grid);
    background: rgba(132, 143, 165, .22);
    color: var(--ink);
}

.sim-tag.chemistry {
    border-color: var(--accent);
    background: rgba(193, 73, 83, .12);
    color: var(--accent-dark);
}

.sim-lessons {
    font-family: var(--font-mono);
    font-size: 12px;
    text-transform: uppercase;
    color: var(--accent-dark);
}

.sim-launch {
    display: flex;
    align-items: center;
    justify-content: space-between;
    min-height: 44px;
    padding: 14px 24px;
    border-top: var(--rule);
    font-family: var(--font-mono);
    font-size: 14px;
}

.sim-card:hover .sim-launch {
    color: var(--accent);
}

#catalog-status {
    color: var(--ink-soft);
}

/* === Footer / Contact === */
.site-footer {
    border-top: var(--rule);
    padding: 24px 0;
    font-size: 14px;
    color: var(--ink-soft);
}

.site-footer.paper-dark {
    border-top: 0;
    padding: 96px 0 40px;
    color: var(--paper-deep);
}

.footer-container {
    display: flex;
    flex-direction: column;
    gap: 72px;
}

.footer-cta {
    display: flex;
    flex-wrap: wrap;
    align-items: flex-end;
    justify-content: space-between;
    gap: 32px;
}

.footer-copy {
    display: flex;
    flex-direction: column;
    gap: 14px;
    max-width: 640px;
}

.footer-copy h2 {
    font-size: clamp(36px, 4.5vw, 52px);
    font-weight: 700;
    line-height: 1.05;
    letter-spacing: -0.01em;
    color: #ffffff;
}

.footer-copy p {
    font-size: 18px;
}

.footer-copy a {
    color: #ffffff;
    text-decoration: underline;
}

.footer-base {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    justify-content: space-between;
    gap: 16px;
    padding-top: 24px;
    border-top: 1px solid var(--ink-soft);
}

.footer-base .logo {
    gap: 10px;
    font-size: 18px;
    color: #ffffff;
}

/* Simple footers (simulation page) keep the single-line layout. */
.site-footer:not(.paper-dark) .footer-container {
    gap: 0;
}

/* === Simulation layout ===
   Stage (scene + graphs) and controls sit side by side whenever both columns
   fit, and wrap to a single column otherwise. Explanation cards follow below. */
.sim-layout {
    display: flex;
    flex-direction: column;
    gap: 32px;
}

.sim-main {
    display: flex;
    flex-wrap: wrap;
    align-items: flex-start;
    gap: 32px;
}

.sim-stage {
    flex: 999 1 560px;
    min-width: 0;
    display: flex;
    flex-direction: column;
    gap: 24px;
}

.sim-main > .controls-panel {
    flex: 1 1 320px;
    min-width: 0;
}

.sim-main > .simulation-dock {
    flex: 1 0 100%;
}

.canvas-wrapper {
    background-color: var(--card);
    background-image:
        linear-gradient(rgba(132, 143, 165, .34) 1px, transparent 1px),
        linear-gradient(90deg, rgba(132, 143, 165, .34) 1px, transparent 1px),
        linear-gradient(rgba(132, 143, 165, .16) 1px, transparent 1px),
        linear-gradient(90deg, rgba(132, 143, 165, .16) 1px, transparent 1px);
    background-size: 100px 100px, 100px 100px, 20px 20px, 20px 20px;
    border: 1px solid var(--ink);
    border-radius: 0;
    padding: 0.75rem;
    display: flex;
    justify-content: center;
    box-shadow: var(--shadow-hard);
}

#gasCanvas {
    width: 100%;
    max-width: 700px;
    height: auto;
    aspect-ratio: 700 / 450;
    display: block;
    border-radius: 0;
    background: var(--card);
}

/* Controls Panel */
.controls-panel {
    display: flex;
    flex-direction: column;
    gap: 1rem;
    background: var(--sim-surface);
    border: 1px solid var(--ink);
    border-radius: 0;
    padding: 1.5rem;
    box-shadow: var(--shadow-hard);
}

.control-row {
    display: flex;
    align-items: center;
    gap: 1rem;
}

.control-row .control-icon {
    font-size: 1.3rem;
    width: 28px;
    text-align: center;
    flex-shrink: 0;
}

.control-row .control-label {
    font-size: 15px;
    font-weight: 500;
    color: var(--ink);
    min-width: 24px;
    flex-shrink: 0;
}

.control-row input[type="range"] {
    flex: 1;
    min-width: 80px;
    accent-color: var(--accent);
    height: 28px;
    cursor: pointer;
}

.control-row .control-value {
    font-family: var(--font-mono);
    font-size: 14px;
    font-weight: 400;
    color: var(--ink);
    min-width: 75px;
    text-align: right;
    font-variant-numeric: tabular-nums;
    flex-shrink: 0;
}

.control-row .control-law {
    font-size: 0.75rem;
    color: var(--accent-dark);
    font-weight: 500;
    min-width: 100px;
    text-align: right;
    flex-shrink: 0;
    cursor: pointer;
    padding: 0.15rem 0.4rem;
    border-radius: 0;
    transition: background 0.15s, color 0.15s;
}

.control-row .control-law:hover {
    background: var(--sim-accent-soft);
    color: var(--accent-dark);
}

/* === Shared simulation components === */

/* Readout cards -------------------------------------------------- */
/* Ruled grid: each cell draws its right and bottom rule, so a short last row stays clean. */
.sim-readouts {
    display: grid;
    gap: 0;
    border-top: 1px solid var(--ink);
    border-left: 1px solid var(--ink);
}
.sim-readouts--3 { grid-template-columns: repeat(3, 1fr); }
.sim-readouts--4 { grid-template-columns: repeat(4, 1fr); }

/* Label reads above the value, as on a lab spec sheet. */
.sim-readout {
    display: flex;
    flex-direction: column-reverse;
    justify-content: flex-end;
    gap: 4px;
    padding: 14px 16px;
    background: var(--sim-surface);
    border-right: 1px solid var(--ink);
    border-bottom: 1px solid var(--ink);
    transition: background 0.2s;
}
.sim-readout__value {
    font-size: 28px;
    font-weight: 700;
    line-height: 1.1;
    color: var(--sim-ink);
    font-variant-numeric: tabular-nums;
}
.sim-readout__label {
    font-family: var(--font-mono);
    font-size: 12px;
    color: var(--sim-muted);
    text-transform: uppercase;
    letter-spacing: 0.04em;
}
.sim-readout--highlight { background: var(--sim-accent-soft); }
.sim-readout--highlight .sim-readout__value { color: var(--sim-accent-dark); }
.sim-readout--warn .sim-readout__value { color: var(--sim-danger); }
.sim-readout--success .sim-readout__value { color: var(--sim-success); }

/* Buttons -------------------------------------------------------- */
.sim-btn {
    min-height: 44px;
    padding: 10px 18px;
    border-radius: var(--sim-radius-sm);
    font-family: inherit;
    font-weight: 500;
    font-size: 15px;
    border: 1px solid var(--ink);
    background: transparent;
    color: var(--ink);
    cursor: pointer;
    transition: background 0.15s, border-color 0.15s, color 0.15s;
}
.sim-btn:hover { background: var(--ink); color: var(--paper); }
.sim-btn:disabled { opacity: 0.4; cursor: default; }
.sim-btn:disabled:hover { background: transparent; color: var(--ink); }
.sim-btn--primary { background: var(--sim-accent); color: #fff; font-weight: 600; box-shadow: 3px 3px 0 var(--ink); }
.sim-btn--primary:hover { background: var(--sim-accent-dark); color: #fff; }
.sim-btn--primary:disabled:hover { background: var(--sim-accent); color: #fff; }
.sim-btn--ghost { background: transparent; color: var(--ink); }
.sim-btn--soft { background: var(--card); color: var(--ink); }
.sim-btn--outline { background: var(--sim-surface); color: var(--sim-muted); border: 1px solid var(--sim-border-strong); }
.sim-btn--outline:hover { background: var(--sim-surface-2); color: var(--ink); }
.sim-btn--block { width: 100%; }
.sim-btn--icon { padding: 0.5rem 0.8rem; font-size: 1rem; line-height: 1; }
.sim-btn.is-active, .sim-btn[aria-pressed="true"] { background: var(--ink); color: var(--paper); }

/* Action row ----------------------------------------------------- */
.sim-actions {
    display: flex;
    gap: 0.75rem;
    flex-wrap: wrap;
    align-items: center;
    padding-top: 0.5rem;
    border-top: 1px solid var(--sim-border);
}

/* Round icon buttons (steppers) ---------------------------------- */
.sim-iconbtn {
    width: 40px;
    height: 40px;
    border-radius: 50%;
    border: 2px solid var(--sim-border-strong);
    background: var(--sim-surface);
    font-family: inherit;
    font-size: 1.3rem;
    font-weight: 700;
    color: var(--sim-accent);
    cursor: pointer;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    transition: all 0.2s;
    flex-shrink: 0;
}
.sim-iconbtn:hover { border-color: var(--sim-accent); background: var(--sim-accent-soft); }
.sim-iconbtn:disabled { opacity: 0.3; cursor: not-allowed; }
.sim-iconbtn--proton { color: var(--accent); }
.sim-iconbtn--neutron { color: var(--ink-soft); }

/* Stepper row ---------------------------------------------------- */
.sim-stepper {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.75rem;
}
.sim-stepper > button {
    flex: 1 1 0;
    min-width: 0;
}
.sim-stepper__display {
    text-align: center;
    font-weight: 700;
    color: var(--sim-ink);
    min-width: 72px;
}
.sim-stepper__value { font-size: 1.3rem; font-variant-numeric: tabular-nums; }
.sim-stepper__unit { margin-left: 4px; font-size: 0.75rem; color: var(--ink-soft); font-weight: 600; }

/* Segmented picker ----------------------------------------------- */
.sim-seg { display: flex; gap: 0.5rem; flex-wrap: wrap; }
.sim-seg__btn {
    flex: 1;
    min-width: 90px;
    padding: 0.55rem 0.6rem;
    min-height: 44px;
    border: 1px solid var(--sim-border-strong);
    border-radius: var(--sim-radius);
    background: var(--sim-surface);
    font-family: inherit;
    font-size: 14px;
    font-weight: 500;
    color: var(--ink);
    cursor: pointer;
    text-align: center;
    transition: all 0.2s;
}
.sim-seg__btn:hover { background: var(--paper-deep); color: var(--ink); }
.sim-seg__btn.is-active, .sim-seg__btn[aria-pressed="true"] { border-color: var(--ink); background: var(--ink); color: var(--paper); }

/* Toolbar / tool buttons ----------------------------------------- */
.sim-toolbar {
    display: flex;
    gap: 0.5rem;
    flex-wrap: wrap;
    align-items: center;
    padding: 0.75rem;
    background: var(--sim-surface);
    border: 1px solid var(--sim-border);
    border-radius: var(--sim-radius-lg);
}
.sim-tool {
    display: inline-flex;
    align-items: center;
    gap: 0.35rem;
    padding: 0.45rem 0.9rem;
    min-height: 44px;
    border: 1px solid var(--sim-border-strong);
    border-radius: var(--sim-radius);
    background: var(--sim-surface);
    font-family: inherit;
    font-size: 14px;
    font-weight: 500;
    color: var(--ink);
    cursor: pointer;
    transition: all 0.15s;
}
.sim-tool:hover { background: var(--paper-deep); color: var(--ink); }
.sim-tool.is-active, .sim-tool[aria-pressed="true"] { border-color: var(--ink); background: var(--ink); color: var(--paper); }
.sim-tool__icon { font-size: 1.1rem; }

/* Chips (quick actions) ------------------------------------------ */
.sim-chip {
    flex: 1;
    min-width: 40px;
    padding: 0.4rem 0.5rem;
    border: 1px solid var(--sim-border-strong);
    border-radius: var(--sim-radius-sm);
    background: var(--sim-surface);
    font-family: inherit;
    font-size: 0.75rem;
    font-weight: 500;
    color: var(--sim-accent-dark);
    cursor: pointer;
    transition: all 0.15s;
}
.sim-chip:hover { border-color: var(--sim-accent); background: var(--sim-accent-soft); }

/* Stat bar ------------------------------------------------------- */
.sim-statbar {
    display: flex;
    gap: 1rem;
    padding: 0.75rem 1rem;
    background: var(--sim-surface);
    border: 1px solid var(--sim-border);
    border-radius: var(--sim-radius-lg);
    align-items: center;
    flex-wrap: wrap;
    justify-content: center;
}
.sim-statbar__item { display: flex; align-items: center; gap: 0.4rem; }
.sim-statbar__label { font-size: 0.7rem; font-weight: 600; color: var(--sim-faint); text-transform: uppercase; letter-spacing: 0.05em; }
.sim-statbar__value { font-size: 1.05rem; font-weight: 700; color: var(--sim-ink); font-variant-numeric: tabular-nums; }
.sim-statbar__unit { font-size: 0.7rem; color: var(--sim-faint); font-weight: 500; }

/* Badges --------------------------------------------------------- */
.sim-badge {
    display: inline-block;
    padding: 0.4rem 1rem;
    border-radius: 0;
    font-size: 0.9rem;
    font-weight: 700;
    letter-spacing: 0.04em;
}
.sim-badge { font-family: var(--font-mono); font-weight: 500; text-transform: uppercase; border: 1px solid currentColor; }
.sim-badge--stable, .sim-badge--liquid { background: var(--sim-success-soft); color: var(--sim-success); }
.sim-badge--unstable { background: var(--sim-warn-soft); color: var(--sim-warn); }
.sim-badge--radioactive, .sim-badge--gas { background: var(--sim-danger-soft); color: var(--sim-danger); }
.sim-badge--impossible { background: var(--paper); color: var(--sim-faint); }
.sim-badge--solid { background: rgba(132, 143, 165, .22); color: var(--ink); }

/* Info bar (nucleus) --------------------------------------------- */
.sim-infobar {
    margin-top: 0.8rem;
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 1rem 1.5rem;
    padding: 0.6rem 0.8rem;
    background: var(--sim-surface-2);
    border-radius: var(--sim-radius);
}
.sim-infobar__header { display: flex; align-items: center; gap: 0.5rem; }
.sim-infobar__name { font-size: 1.4rem; font-weight: 800; color: var(--sim-ink); }
.sim-infobar__symbol { font-size: 1.1rem; color: var(--ink-soft); font-weight: 600; }
.sim-infobar__props { display: flex; gap: 0.6rem; }
.sim-infobar__item { text-align: center; padding: 0.3rem 0.5rem; background: var(--sim-surface); border-radius: var(--sim-radius-sm); min-width: 56px; }
.sim-infobar__value { font-size: 1.1rem; font-weight: 800; color: var(--sim-ink); }
.sim-infobar__label { font-size: 0.6rem; color: var(--sim-faint); font-weight: 600; text-transform: uppercase; letter-spacing: 0.05em; }
.sim-infobar__desc { font-size: 0.72rem; color: var(--sim-faint); margin: 0; }

/* Small helper text ---------------------------------------------- */
.sim-help { font-size: 0.75rem; color: var(--sim-faint); text-align: center; margin-top: 0.4rem; }

/* Optional SimLib default panel chrome --------------------------- */
.sim-panel { display: flex; flex-wrap: wrap; gap: 0.75rem; align-items: center; padding: 0.75rem; }
.sim-row { display: flex; gap: 0.75rem; align-items: center; }
.sim-panel-btn {
    padding: 0.5rem 1.25rem;
    border: none;
    border-radius: var(--sim-radius-sm);
    background: var(--sim-accent);
    color: #fff;
    font-family: inherit;
    font-weight: 600;
    font-size: 0.85rem;
    cursor: pointer;
}
.sim-panel-slider { display: flex; align-items: center; gap: 0.5rem; font-size: 0.85rem; }
.sim-panel-readout { text-align: center; }
.sim-panel-readout__value { font-weight: 800; color: var(--sim-ink); }
.sim-panel-readout__label { font-size: 0.7rem; color: var(--sim-muted); text-transform: uppercase; }

/* Explanation cards */
.sim-sidebar {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 24px;
}

.equation-card {
    background: var(--sim-surface);
    border: 1px solid var(--ink);
    border-radius: 0;
    padding: 1.25rem;
    box-shadow: none;
}

.equation-card h3 {
    font-size: 20px;
    font-weight: 600;
    color: var(--ink);
    margin-bottom: 0.5rem;
}

.equation-formula {
    font-size: 1.15rem;
    font-weight: 500;
    color: var(--accent-dark);
    font-family: var(--font-mono);
    font-style: normal;
    margin-bottom: 0.5rem;
    padding: 0.3rem 0.7rem;
    background: var(--sim-accent-soft);
    border-radius: 0;
    display: inline-block;
}

.equation-card .eq-explanation {
    font-size: 0.85rem;
    color: var(--ink-soft);
    line-height: 1.55;
}

.equation-card .eq-sub {
    font-size: 0.85rem;
    color: var(--ink-soft);
    margin-top: 0.5rem;
    padding: 0.5rem 0.7rem;
    background: var(--paper);
    border-radius: 0;
    font-family: var(--font-mono);
    font-style: normal;
}

.equation-card .eq-sub .hl {
    color: var(--accent-dark);
    font-weight: 700;
}

/* === Shared simulation page layout === */
.sim-page-header {
    padding: 48px 0 32px;
}

.sim-page-header .container {
    display: grid;
    grid-template-columns: minmax(0, 1fr) auto;
    align-items: end;
    gap: 12px 24px;
}

.sim-page-header h1,
.sim-page-header p {
    grid-column: 1;
    max-width: 720px;
}

.sim-page-header h1 {
    font-size: clamp(40px, 5vw, 60px);
    font-weight: 700;
    line-height: 1;
    letter-spacing: -0.01em;
}

.sim-page-header p {
    color: var(--ink-soft);
    font-size: 18px;
    line-height: 1.55;
}

.sim-page-header #lesson-launcher {
    grid-column: 2;
    grid-row: 1 / span 2;
}

.sim-page-header #lesson-launcher .guided-launcher {
    margin: 0;
}

@media (max-width: 768px) {
    .sim-page-header .container { grid-template-columns: minmax(0, 1fr); }
    .sim-page-header #lesson-launcher { grid-column: 1; grid-row: auto; }
    .sim-page-header #lesson-launcher .guided-launcher { justify-content: flex-start; }
}

.sim-canvas-area {
    padding: 0 0 96px;
}

.sim-canvas-area .container,
.sim-page-header .container {
    max-width: 1280px;
}

.primary-nav .sim-back-link {
    min-height: 44px;
    display: inline-flex;
    align-items: center;
}

/* ── Law Popup Modal ── */
.modal-overlay {
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.35);
    z-index: 2000;
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.25s, visibility 0.25s;
}

.modal-overlay.active {
    opacity: 1;
    visibility: visible;
}

.modal-panel {
    position: fixed;
    top: 0;
    right: 0;
    width: 100%;
    max-width: 420px;
    height: 100%;
    background: var(--sim-surface);
    z-index: 2001;
    box-shadow: -8px 0 32px rgba(0, 0, 0, 0.1);
    transform: translateX(100%);
    transition: transform 0.3s cubic-bezier(0.25, 0.46, 0.45, 0.94);
    display: flex;
    flex-direction: column;
    overflow-y: auto;
}

.modal-panel.active {
    transform: translateX(0);
}

.modal-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 1.5rem 1.5rem 0;
}

.modal-header h2 {
    font-size: 1.2rem;
    font-weight: 700;
    color: var(--ink);
}

.modal-close {
    background: none;
    border: none;
    font-size: 1.5rem;
    color: var(--ink-soft);
    cursor: pointer;
    padding: 0.25rem;
    line-height: 1;
    transition: color 0.15s;
}

.modal-close:hover {
    color: var(--ink);
}

.modal-body {
    padding: 1.5rem;
    flex: 1;
}

.modal-formula {
    font-size: 1.4rem;
    font-weight: 700;
    color: var(--accent-dark);
    font-family: var(--font-mono);
    font-style: normal;
    padding: 0.6rem 1rem;
    background: var(--sim-accent-soft);
    border-radius: 0;
    display: inline-block;
    margin-bottom: 1rem;
}

.modal-body .eq-explanation {
    font-size: 0.95rem;
    color: var(--ink-soft);
    line-height: 1.6;
    margin-bottom: 1rem;
}

.modal-body .eq-detail {
    font-size: 0.85rem;
    color: var(--ink-soft);
    line-height: 1.5;
    padding: 0.75rem 1rem;
    background: var(--paper);
    border-radius: 0;
    border-left: 3px solid var(--accent);
}

/* === Responsive === */

@media (max-width: 768px) {
    .hero {
        padding: 8rem 0 4rem;
    }

    .hero h1 {
        font-size: 2.25rem;
    }

    .hero-logo-icon {
        height: 160px;
    }

    .section {
        padding: 3.5rem 0;
    }

    .section-title {
        font-size: 1.6rem;
    }

    .primary-nav ul {
        gap: 1rem;
    }

    .primary-nav a {
        font-size: 0.825rem;
    }

    .goals-list li {
        flex-direction: column;
        gap: 0.75rem;
    }

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

    .sim-page-header h1 {
        font-size: 1.75rem;
    }

    .control-row .control-law {
        display: none;
    }

    .sim-readouts--3,
    .sim-readouts--4 {
        grid-template-columns: repeat(2, 1fr);
    }

}

@media (max-width: 480px) {
    .container {
        padding: 0 1rem;
    }

    .hero h1 {
        font-size: 1.8rem;
    }

    .hero-subtitle {
        font-size: 1rem;
    }

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

    .contact-links {
        flex-direction: column;
        align-items: center;
    }
}

/* ── Fullscreen: the simulation fills the whole screen ── */
.btn-fullscreen {
    position: absolute;
    top: 0.6rem;
    right: 0.6rem;
    z-index: 10;
    background: rgba(244, 239, 226, 0.9);
    border: 1px solid var(--ink);
    border-radius: 0;
    padding: 0.3rem 0.5rem;
    font-size: 1.1rem;
    cursor: pointer;
    line-height: 1;
    transition: background 0.2s, border-color 0.2s;
    color: var(--ink-soft);
}
.btn-fullscreen:hover {
    background: var(--sim-surface);
    border-color: var(--accent);
    color: var(--accent);
}

/* In fullscreen we keep the controls (they are part of the simulation);
   only the reference/equation sidebar and the back link are hidden. */
.fs-active .sim-sidebar,
.fs-active .sim-back-link { display: none !important; }

.sim-layout:fullscreen,
.sim-layout:-webkit-full-screen {
    display: flex !important;
    flex-direction: column !important;
    align-items: stretch;
    justify-content: flex-start;
    gap: 0.5rem;
    padding: 0.5rem;
    width: 100vw;
    height: 100vh;
    /* !important: build-a-nucleus.html overrides .sim-layout max-width in its
       own page-level <style>, which would otherwise cap the fullscreen size. */
    max-width: none !important;
    max-height: none !important;
    margin: 0 !important;
    background: var(--paper);
    overflow: hidden;
}

.sim-layout:fullscreen .sim-main,
.sim-layout:-webkit-full-screen .sim-main {
    display: flex;
    flex-direction: column;
    flex-wrap: nowrap;
    align-items: stretch;
    gap: 0.5rem;
    flex: 1 1 auto;
    min-height: 0;   /* allow the canvas column to shrink inside the viewport */
    width: 100%;
}

.sim-layout:fullscreen .sim-stage,
.sim-layout:-webkit-full-screen .sim-stage {
    flex: 1 1 auto;
    min-height: 0;
    gap: 0.5rem;
}

/* Landscape fullscreen keeps the controls beside the scene. */
@media (min-aspect-ratio: 4/3) {
    .sim-layout:fullscreen .sim-main,
    .sim-layout:-webkit-full-screen .sim-main { flex-direction: row; }
    .sim-layout:fullscreen .sim-main > .controls-panel,
    .sim-layout:-webkit-full-screen .sim-main > .controls-panel {
        flex: 0 0 340px;
        max-height: none;
        align-self: stretch;
    }
}

/* Canvas wrapper grows to take all remaining vertical space */
.sim-layout:fullscreen .canvas-wrapper,
.sim-layout:fullscreen .proj-canvas-wrap,
.sim-layout:-webkit-full-screen .canvas-wrapper,
.sim-layout:-webkit-full-screen .proj-canvas-wrap {
    padding: 0;
    box-shadow: none;
    border: none;
    background: transparent;
    flex: 1 1 auto;
    min-height: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    overflow: hidden;
}

/* The canvas itself scales up to fill the whole screen while keeping its
   aspect ratio (object-fit keeps it undistorted on letterboxed screens). */
.sim-layout:fullscreen .canvas-wrapper canvas,
.sim-layout:fullscreen .proj-canvas-wrap canvas,
.sim-layout:-webkit-full-screen .canvas-wrapper canvas,
.sim-layout:-webkit-full-screen .proj-canvas-wrap canvas {
    width: 100% !important;
    height: 100% !important;
    max-width: 100% !important;
    max-height: 100% !important;
    aspect-ratio: auto !important;
    object-fit: contain;
    border-radius: 0;
}

/* Controls stay available in fullscreen, in a compact scrollable strip */
.sim-layout:fullscreen .controls-panel,
.sim-layout:-webkit-full-screen .controls-panel {
    flex: 0 0 auto;
    max-height: 34vh;
    overflow-y: auto;
    padding: 0.75rem 1rem;
}

.sim-layout:fullscreen .btn-fullscreen,
.sim-layout:-webkit-full-screen .btn-fullscreen {
    background: rgba(45, 45, 42, 0.6);
    border-color: var(--ink-soft);
    color: #fff;
    top: 0.8rem;
    right: 0.8rem;
}
.sim-layout:fullscreen .btn-fullscreen:hover,
.sim-layout:-webkit-full-screen .btn-fullscreen:hover {
    background: rgba(45, 45, 42, 0.85);
    border-color: #fff;
    color: #fff;
}