/* =====================================================================
   ML Resources Hub — main stylesheet
   Minimalist, light theme. Serif display + sans body. Hairline borders.
   Indigo accent with terracotta pops.
   Class names preserved so existing pages keep working.
===================================================================== */

@import url('https://fonts.googleapis.com/css2?family=Fraunces:ital,opsz,wght@0,9..144,400;0,9..144,500;0,9..144,600;1,9..144,400;1,9..144,500&family=Dancing+Script:wght@600;700&family=Inter:wght@400;500;600;700&family=JetBrains+Mono:wght@400;500&display=swap');

:root {
    /* New palette */
    --bg: #fbfaf7;              /* warm off-white page background */
    --surface: #ffffff;         /* cards */
    --ink: #1a1a1a;             /* primary text */
    --ink-soft: #2a2a2a;
    --muted: #5f5f5f;           /* secondary text */
    --hairline: #e8e5dd;        /* subtle borders */
    --hairline-strong: #d6d3ca;
    --accent: #4f46e5;          /* indigo — links, primary actions */
    --accent-hover: #3730a3;
    --accent-soft: #eef2ff;     /* indigo wash for chips, inline code */
    --accent-warm: #ea7959;     /* terracotta pop — hover hints, icons */
    --accent-warm-soft: #fdf0eb;

    /* Legacy variable names — kept so per-page inline <style> blocks
       that say var(--primary-color) etc. keep resolving correctly. */
    --primary-color: var(--ink);
    --secondary-color: var(--accent);
    --accent-color: var(--accent-warm);
    --text-color: var(--ink-soft);
    --light-bg: #f5f3ee;
    --white: #ffffff;

    /* Typography */
    --font-serif: 'Fraunces', Georgia, 'Times New Roman', serif;
    --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Tahoma, sans-serif;
    --font-mono: 'JetBrains Mono', 'Fira Code', ui-monospace, Menlo, monospace;
}

* { margin: 0; padding: 0; box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
    font-family: var(--font-sans);
    font-feature-settings: 'cv11', 'ss01';
    line-height: 1.65;
    color: var(--ink-soft);
    background: var(--bg);
    -webkit-font-smoothing: antialiased;
    text-rendering: optimizeLegibility;
}

h1, h2, h3, h4 {
    font-family: var(--font-serif);
    font-weight: 500;
    letter-spacing: -0.015em;
    line-height: 1.2;
    color: var(--ink);
}
h1 { font-size: clamp(2.25rem, 4.5vw, 3.5rem); letter-spacing: -0.025em; }
h2 { font-size: 1.75rem; }
h3 { font-size: 1.2rem; }

p { color: var(--ink-soft); }

a {
    color: var(--accent);
    text-decoration: none;
    transition: color 0.2s ease;
}
a:hover { color: var(--accent-hover); }

::selection { background: var(--accent-warm-soft); color: var(--ink); }


/* ---------- Navbar ---------- */
.navbar {
    background: rgba(251, 250, 247, 0.85);
    backdrop-filter: saturate(160%) blur(12px);
    -webkit-backdrop-filter: saturate(160%) blur(12px);
    border-bottom: 1px solid var(--hairline);
    padding: 1rem 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    position: fixed;
    width: 100%;
    top: 0;
    z-index: 1000;
}

.nav-brand {
    color: var(--ink);
    font-family: var(--font-serif);
    font-size: 1.35rem;
    font-weight: 500;
    letter-spacing: -0.01em;
}

/* Brand lockup: mesh mark + "Layer" (serif) + "wise" (script) */
.brand-lockup {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    text-decoration: none;
    color: inherit;
}
.brand-mark {
    width: 30px;
    height: 30px;
    display: block;
    flex: none;
}
.brand-word { line-height: 1; }
.brand-layer {
    font-family: var(--font-serif);
    font-weight: 600;
    color: var(--ink);
}
.brand-wise {
    font-family: 'Dancing Script', cursive;
    font-weight: 700;
    color: #7c3aed;
    margin-left: 1px;
    font-size: 1.08em;
}

.nav-links a {
    color: var(--muted);
    font-size: 0.92rem;
    font-weight: 500;
    margin-left: 2rem;
    position: relative;
    padding: 0.25rem 0;
    transition: color 0.2s ease;
}
.nav-links a:hover { color: var(--ink); }
.nav-links a.active { color: var(--ink); }
.nav-links a.active::after {
    content: '';
    position: absolute;
    left: 0; right: 0; bottom: -6px;
    height: 2px;
    background: var(--accent);
    border-radius: 1px;
}

.nav-toggle {
    display: none;
    color: var(--ink);
    font-size: 1.25rem;
    cursor: pointer;
}


/* ---------- Search ---------- */
/* Brand takes the left; nav-links + search trigger group on the right. */
.navbar .nav-brand { margin-right: auto; }

.search-trigger {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    margin-left: 2rem;
    padding: 0.4rem 0.7rem;
    font: inherit;
    font-size: 0.85rem;
    color: var(--muted);
    background: var(--surface);
    border: 1px solid var(--hairline-strong);
    border-radius: 8px;
    cursor: pointer;
    transition: color 0.2s ease, border-color 0.2s ease, background 0.2s ease;
}
.search-trigger:hover {
    color: var(--ink);
    border-color: var(--accent);
    background: var(--accent-soft);
}
.search-trigger .fa-search { font-size: 0.8rem; }
.search-trigger-kbd {
    font-family: var(--font-mono);
    font-size: 0.72rem;
    line-height: 1;
    padding: 0.15rem 0.35rem;
    color: var(--muted);
    background: var(--light-bg);
    border: 1px solid var(--hairline-strong);
    border-radius: 4px;
}

/* Overlay + modal */
.search-overlay {
    display: none;
    position: fixed;
    inset: 0;
    z-index: 2000;
    background: rgba(26, 26, 26, 0.38);
    backdrop-filter: blur(3px);
    -webkit-backdrop-filter: blur(3px);
    padding: 12vh 1rem 2rem;
}
.search-overlay.open { display: block; }
body.search-open { overflow: hidden; }

.search-modal {
    max-width: 640px;
    margin: 0 auto;
    background: var(--surface);
    border: 1px solid var(--hairline);
    border-radius: 14px;
    box-shadow: 0 24px 60px rgba(26, 26, 26, 0.28);
    overflow: hidden;
    display: flex;
    flex-direction: column;
    max-height: 76vh;
}

.search-inputbar {
    display: flex;
    align-items: center;
    gap: 0.7rem;
    padding: 0.9rem 1.1rem;
    border-bottom: 1px solid var(--hairline);
}
.search-inputbar-icon { color: var(--muted); font-size: 0.95rem; }
.search-input {
    flex: 1;
    border: none;
    outline: none;
    background: transparent;
    font-family: var(--font-sans);
    font-size: 1.05rem;
    color: var(--ink);
}
.search-input::placeholder { color: var(--muted); }
.search-esc {
    font-family: var(--font-mono);
    font-size: 0.72rem;
    color: var(--muted);
    padding: 0.2rem 0.4rem;
    border: 1px solid var(--hairline-strong);
    border-radius: 4px;
}

.search-status {
    padding: 0.6rem 1.1rem;
    font-size: 0.82rem;
    color: var(--muted);
    border-bottom: 1px solid var(--hairline);
}
.search-status:empty { display: none; }
.search-eg {
    font: inherit;
    color: var(--accent);
    background: none;
    border: none;
    padding: 0;
    cursor: pointer;
    border-bottom: 1px dotted currentColor;
}
.search-eg:hover { color: var(--accent-hover); }

.search-results {
    list-style: none;
    margin: 0;
    padding: 0.35rem;
    overflow-y: auto;
}
.search-result a {
    display: block;
    padding: 0.6rem 0.75rem;
    border-radius: 9px;
    text-decoration: none;
    color: inherit;
}
.search-result.active a,
.search-result a:hover { background: var(--accent-soft); }

.search-result-head {
    display: flex;
    align-items: baseline;
    gap: 0.6rem;
    margin-bottom: 0.15rem;
}
.search-result-title {
    font-family: var(--font-serif);
    font-size: 1rem;
    font-weight: 500;
    color: var(--ink);
}
.search-cat {
    margin-left: auto;
    flex: none;
    font-size: 0.72rem;
    color: var(--muted);
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 20px;
    padding: 0.1rem 0.55rem;
    white-space: nowrap;
}
.search-snippet {
    font-size: 0.83rem;
    line-height: 1.45;
    color: var(--muted);
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
}
.search-result mark {
    background: var(--accent-warm-soft);
    color: var(--ink);
    border-radius: 2px;
    padding: 0 1px;
}

@media (max-width: 768px) {
    .search-trigger-label { display: none; }
    .search-trigger-kbd { display: none; }
    .search-trigger { margin-left: 0.75rem; padding: 0.4rem 0.55rem; }
    .search-overlay { padding: 8vh 0.75rem 1rem; }
}


/* ---------- Hero ---------- */
.hero {
    background:
        radial-gradient(circle at 18% 28%, rgba(234, 121, 89, 0.14), transparent 55%),
        radial-gradient(circle at 82% 70%, rgba(79, 70, 229, 0.12), transparent 55%),
        var(--bg);
    min-height: 62vh;
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    color: var(--ink);
    margin-top: 64px;
    padding: 5rem 1.5rem 4rem;
    position: relative;
    overflow: hidden;
}

.hero-content { max-width: 720px; }

.hero-content h1 {
    font-size: clamp(2.5rem, 5.5vw, 3.75rem);
    font-weight: 500;
    margin-bottom: 1.25rem;
    color: var(--ink);
}
.hero-content h1 em {
    font-style: italic;
    color: var(--accent);
    font-weight: 400;
}

.hero-content p {
    font-size: 1.15rem;
    color: var(--muted);
    max-width: 560px;
    margin: 0 auto;
}


/* ---------- Layout container ---------- */
.container {
    max-width: 1100px;
    margin: 3.5rem auto;
    padding: 0 1.5rem;
}


/* ---------- Feature cards (homepage) ---------- */
.features {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
    gap: 1.5rem;
    margin-top: 1rem;
}

.feature-card {
    background: var(--surface);
    padding: 2rem 1.75rem;
    border: 1px solid var(--hairline);
    border-radius: 14px;
    text-align: left;
    transition: transform 0.25s ease, border-color 0.25s ease, box-shadow 0.25s ease;
    position: relative;
    overflow: hidden;
}
.feature-card::before {
    content: '';
    position: absolute;
    top: 0; left: 0; right: 0;
    height: 2px;
    background: linear-gradient(90deg, var(--accent), var(--accent-warm));
    transform: scaleX(0);
    transform-origin: left;
    transition: transform 0.35s ease;
}
.feature-card:hover {
    transform: translateY(-4px);
    border-color: var(--hairline-strong);
    box-shadow: 0 10px 28px -14px rgba(26, 26, 26, 0.18);
}
.feature-card:hover::before { transform: scaleX(1); }

.feature-card i {
    font-size: 1.15rem;
    color: var(--accent);
    margin-bottom: 1.1rem;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    background: var(--accent-soft);
    border-radius: 10px;
    width: 42px;
    height: 42px;
}
.feature-card h2 {
    font-family: var(--font-serif);
    font-size: 1.3rem;
    margin-bottom: 0.5rem;
    color: var(--ink);
}
.feature-card p {
    color: var(--muted);
    font-size: 0.95rem;
    margin-bottom: 1.25rem;
    line-height: 1.55;
}


/* ---------- Buttons ---------- */
.btn {
    display: inline-flex;
    align-items: center;
    gap: 0.45rem;
    padding: 0.6rem 1.1rem;
    background: var(--ink);
    color: var(--white);
    font-family: var(--font-sans);
    font-size: 0.9rem;
    font-weight: 500;
    text-decoration: none;
    border: 1px solid var(--ink);
    border-radius: 8px;
    margin-top: 0.5rem;
    transition: background 0.2s ease, border-color 0.2s ease, transform 0.2s ease;
}
.btn::after {
    content: '→';
    font-family: var(--font-sans);
    transition: transform 0.2s ease;
}
.btn:hover {
    background: var(--accent);
    border-color: var(--accent);
    color: var(--white);
}
.btn:hover::after { transform: translateX(3px); }


/* ---------- Footer ---------- */
footer {
    border-top: 1px solid var(--hairline);
    background: var(--bg);
    color: var(--muted);
    padding: 2rem 0;
    margin-top: 4rem;
}
.footer-content {
    max-width: 1100px;
    margin: 0 auto;
    padding: 0 1.5rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 0.9rem;
}
.social-links a {
    color: var(--muted);
    margin-left: 1.25rem;
    font-size: 1.2rem;
    transition: color 0.2s ease;
}
.social-links a:hover { color: var(--accent); }


/* ---------- Page header (inner pages) ---------- */
.page-header {
    padding: 1rem 0 2.5rem;
    margin: 0 0 2rem;
    border-bottom: 1px solid var(--hairline);
    position: relative;
}
.page-header .eyebrow {
    display: inline-block;
    font-family: var(--font-sans);
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--accent);
    letter-spacing: 0.14em;
    text-transform: uppercase;
    margin-bottom: 0.85rem;
    padding: 0.25rem 0.65rem;
    background: var(--accent-soft);
    border-radius: 999px;
}
.page-header h1 {
    font-size: clamp(2rem, 3.6vw, 2.85rem);
    margin-bottom: 0.6rem;
    color: var(--ink);
}
.page-header h1 em {
    font-style: italic;
    color: var(--accent);
    font-weight: 400;
}
.page-header .lead {
    margin: 0;
    max-width: 640px;
    color: var(--muted);
    font-size: 1.1rem;
    line-height: 1.55;
}

/* ---------- Content sections (theory / practice / etc.) ---------- */
.content-section {
    background: var(--surface);
    padding: 2.25rem 2.5rem;
    border: 1px solid var(--hairline);
    border-radius: 14px;
    margin-bottom: 1.5rem;
}
.content-section h2 {
    color: var(--ink);
    margin-bottom: 1.25rem;
    padding-bottom: 0.85rem;
    border-bottom: 1px solid var(--hairline);
    font-size: 1.6rem;
}
.content-section h3 {
    color: var(--ink);
    margin: 1.25rem 0 0.5rem;
    font-family: var(--font-sans);
    font-size: 1.05rem;
    font-weight: 600;
    letter-spacing: -0.005em;
}
.content-section p { color: var(--ink-soft); }
.content-section ul, .content-section ol { margin: 0.5rem 0 1rem 1.25rem; color: var(--ink-soft); }
.content-section li { margin-bottom: 0.35rem; }


/* ---------- Concept / component grids ---------- */
.concept-grid, .component-grid, .resource-grid, .topic-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
    gap: 1.25rem;
    margin-bottom: 1.75rem;
}

.concept-card, .component-card {
    background: var(--light-bg);
    padding: 1.5rem;
    border: 1px solid var(--hairline);
    border-radius: 12px;
}
.concept-card h3, .component-card h3 {
    color: var(--ink);
    margin-bottom: 0.75rem;
    font-family: var(--font-sans);
    font-size: 1rem;
    font-weight: 600;
}
.concept-card ul, .component-card ul { list-style: none; padding: 0; }
.concept-card li, .component-card li {
    margin-bottom: 0.45rem;
    padding-left: 1.1rem;
    position: relative;
    color: var(--muted);
    font-size: 0.93rem;
}
.concept-card li::before, .component-card li::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0.6em;
    width: 5px; height: 5px;
    background: var(--accent);
    border-radius: 50%;
}


/* ---------- Resource / topic cards (link cards) ---------- */
.resource-card, .topic-card {
    background: var(--surface);
    padding: 1.5rem;
    border: 1px solid var(--hairline);
    border-radius: 12px;
    text-decoration: none;
    color: var(--ink);
    transition: transform 0.25s ease, border-color 0.25s ease, box-shadow 0.25s ease;
    display: block;
}
.resource-card:hover, .topic-card:hover {
    transform: translateY(-3px);
    border-color: var(--accent);
    box-shadow: 0 8px 20px -10px rgba(79, 70, 229, 0.22);
}
.resource-card i {
    font-size: 1.25rem;
    color: var(--accent);
    margin-bottom: 0.75rem;
}
.resource-card h3, .topic-card h3 {
    color: var(--ink);
    margin-bottom: 0.4rem;
    font-family: var(--font-sans);
    font-size: 1.02rem;
    font-weight: 600;
}
.resource-card p, .topic-card p {
    color: var(--muted);
    font-size: 0.9rem;
    line-height: 1.5;
}


/* ---------- Code blocks ---------- */
.code-example {
    background: var(--light-bg);
    padding: 1.5rem;
    border: 1px solid var(--hairline);
    border-radius: 12px;
    margin-bottom: 1.5rem;
}
.code-example h3 {
    color: var(--ink);
    margin-bottom: 0.75rem;
    font-family: var(--font-sans);
    font-size: 1rem;
    font-weight: 600;
}
.code-example pre {
    background: #1a1a1a;
    color: #e8e8e8;
    padding: 1.25rem;
    border-radius: 8px;
    overflow-x: auto;
    font-size: 0.85rem;
    line-height: 1.6;
}
.code-example code { font-family: var(--font-mono); }

code:not(pre code) {
    font-family: var(--font-mono);
    background: var(--accent-soft);
    color: var(--accent-hover);
    padding: 0.1rem 0.4rem;
    border-radius: 4px;
    font-size: 0.88em;
}


/* ---------- Alert ---------- */
.alert {
    padding: 1rem 1.25rem;
    border-radius: 10px;
    margin-bottom: 1.5rem;
    border: 1px solid;
    font-size: 0.95rem;
}
.alert-info {
    background: var(--accent-soft);
    color: var(--accent-hover);
    border-color: rgba(79, 70, 229, 0.18);
}
.alert i { margin-right: 0.5rem; }


/* ---------- Lead text ---------- */
.lead {
    font-size: 1.2rem;
    color: var(--muted);
    margin-bottom: 2rem;
    line-height: 1.55;
}


/* ---------- Topic TL;DR pages (one short page per topic) ---------- */

/* Narrower container for prose-style pages */
.container-narrow {
    max-width: 720px;
    margin: 3rem auto;
    padding: 0 1.5rem;
}

/* Two-column layout: main content + sticky sidebar for external resources */
.topic-layout {
    display: grid;
    grid-template-columns: minmax(0, 1fr) 280px;
    gap: 3rem;
    max-width: 1080px;
    margin: 3rem auto;
    padding: 0 1.5rem;
}
.topic-main { min-width: 0; }
.topic-sidebar {
    position: sticky;
    top: 90px;
    align-self: start;
    max-height: calc(100vh - 110px);
    overflow-y: auto;
    /* Subtle scrollbar (Firefox + WebKit) */
    scrollbar-width: thin;
    scrollbar-color: var(--hairline) transparent;
}
.topic-sidebar::-webkit-scrollbar { width: 6px; }
.topic-sidebar::-webkit-scrollbar-track { background: transparent; }
.topic-sidebar::-webkit-scrollbar-thumb {
    background: var(--hairline);
    border-radius: 3px;
}
.topic-sidebar::-webkit-scrollbar-thumb:hover { background: var(--muted); }

/* Tier + notation controls row (replaces the bare .level-tabs block in
   templates/topic.html). Tabs sit on the left; notation toggle on the right. */
.tier-controls {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 0.6rem 1.25rem;
    margin: 0 0 2rem;
}
.tier-controls .level-tabs { margin: 0; }

.notation-toggle {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    margin-left: auto;
    font-family: var(--font-sans);
    font-size: 0.8rem;
    color: var(--muted);
}
.notation-toggle .seg {
    display: inline-flex;
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 999px;
    padding: 0.2rem;
    gap: 0.15rem;
}
.notation-toggle .seg button {
    padding: 0.3rem 0.75rem;
    font-size: 0.78rem;
    font-weight: 500;
    color: var(--muted);
    background: transparent;
    border: none;
    border-radius: 999px;
    cursor: pointer;
    font-family: inherit;
    transition: background 0.2s ease, color 0.2s ease;
}
.notation-toggle .seg button:hover { color: var(--ink); }
.notation-toggle .seg button.active {
    background: var(--surface);
    color: var(--ink);
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.08);
}

/* Hide notation toggle on tiers without an alternate (intuition) and on
   pages that contain no .notation-plain elements at all. */
body[data-tier="intuition"] .notation-toggle { display: none; }
body:not(:has(.notation-plain)) .notation-toggle { display: none; }

/* Notation alternates: default = standard (math); plain mode swaps in
   the spelled-out form. */
.notation-plain { display: none; }
body[data-notation="plain"] .notation-standard { display: none; }
body[data-notation="plain"] .notation-plain { display: block; }

/* Sidebar "Where to learn more" — items can be tier-tagged so the sidebar
   matches the active tier. Items without data-tier always show (legacy pages). */
.learn-more li[data-tier] { display: none; }
body[data-tier="intuition"]    .learn-more li[data-tier="intuition"]    { display: block; }
body[data-tier="fundamentals"] .learn-more li[data-tier="fundamentals"] { display: block; }
body[data-tier="indepth"]      .learn-more li[data-tier="indepth"]      { display: block; }

/* Plain-mode formula narration: short "in words" paragraph after a formula
   that names unfamiliar notation and walks through what's being computed. */
.formula-narration {
    margin: 0.5rem 0 0.85rem;
    padding: 0.6rem 0.85rem;
    background: rgba(79, 70, 229, 0.05);
    border-left: 2px solid rgba(79, 70, 229, 0.25);
    border-radius: 0 4px 4px 0;
    font-size: 0.92rem;
    color: var(--ink-soft);
    line-height: 1.6;
}
.formula-narration strong { color: var(--ink); }
.formula-narration code {
    background: rgba(255, 255, 255, 0.55);
    color: var(--accent-hover);
    padding: 0.02rem 0.35rem;
    border-radius: 4px;
    font-size: 0.88em;
}

/* Difficulty selector (segmented control) */
.level-tabs {
    display: inline-flex;
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 999px;
    padding: 0.25rem;
    margin: 0 0 2rem;
    gap: 0.2rem;
    font-family: var(--font-sans);
}
.level-tab {
    padding: 0.4rem 1rem;
    font-size: 0.82rem;
    font-weight: 500;
    color: var(--muted);
    background: transparent;
    border: none;
    border-radius: 999px;
    cursor: pointer;
    transition: background 0.2s ease, color 0.2s ease;
    font-family: inherit;
}
.level-tab:hover { color: var(--ink); }
.level-tab.active {
    background: var(--surface);
    color: var(--ink);
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.08);
}

/* Content levels — only the active one is visible.
   Default (no JS): "intuition" is shown. */
.topic-level { display: none; }
.topic-level[data-level="intuition"] { display: block; }
.topic-level.active { display: block; }
.topic-level:not(.active)[data-level="intuition"] { display: none; }

/* GNN message-passing viz — click any node, watch its signal propagate */
.viz-gnn { padding: 1.25rem 1.5rem 1.5rem; }
.viz-gnn-controls {
    display: flex;
    gap: 0.45rem;
    flex-wrap: wrap;
    align-items: center;
    margin-bottom: 0.85rem;
}
.viz-gnn-controls button,
.viz-gnn-controls select {
    padding: 0.35rem 0.85rem;
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 6px;
    color: var(--ink);
    font-family: var(--font-sans);
    font-size: 0.82rem;
    font-weight: 500;
    cursor: pointer;
    transition: background 0.18s ease, border-color 0.18s ease, color 0.18s ease;
}
.viz-gnn-controls button:hover,
.viz-gnn-controls select:hover {
    background: var(--accent-soft);
    border-color: var(--accent);
    color: var(--accent-hover);
}
.viz-gnn-round {
    margin-left: auto;
    padding: 0.25rem 0.7rem;
    background: var(--accent-soft);
    color: var(--accent-hover);
    border-radius: 999px;
    font-family: var(--font-mono);
    font-size: 0.82rem;
    font-weight: 600;
}
.viz-gnn-canvas-wrap {
    background: var(--bg);
    border-radius: 8px;
    padding: 0.5rem;
    margin-bottom: 1rem;
}
.viz-gnn-canvas-wrap canvas {
    display: block;
    width: 100%;
    height: auto;
    cursor: pointer;
    touch-action: none;
}
.viz-gnn-caption {
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 10px;
    padding: 0.85rem 1.1rem;
    font-size: 0.9rem;
    color: var(--ink-soft);
    line-height: 1.55;
}
.viz-gnn-caption strong { color: var(--accent-hover); }


/* DNN forward-pass viz — network diagram with per-neuron mini-heatmaps */
.viz-dnn { padding: 1.25rem 1.5rem 1.5rem; }
.viz-task-banner {
    display: flex;
    align-items: baseline;
    gap: 0.7rem;
    padding: 0.7rem 0.9rem;
    margin-bottom: 0.8rem;
    background: rgba(79, 70, 229, 0.06);
    border-left: 3px solid var(--accent);
    border-radius: 4px;
    font-size: 0.92rem;
    line-height: 1.45;
}
.viz-task-label {
    flex: 0 0 auto;
    font-weight: 700;
    color: var(--accent);
    text-transform: uppercase;
    letter-spacing: 0.06em;
    font-size: 0.74rem;
}
.viz-task-text { color: var(--text); }
.viz-task-text code {
    background: rgba(0, 0, 0, 0.06);
    padding: 0 0.25em;
    border-radius: 3px;
    font-size: 0.92em;
}
.viz-dnn-canvas-wrap {
    background: var(--bg);
    border-radius: 8px;
    padding: 0.5rem;
    margin-bottom: 1rem;
    position: relative;
}
/* Scroll-spy anchor overlays — invisible, just observed for IntersectionObserver */
.viz-fig-anchor {
    position: absolute;
    left: 0;
    width: 100%;
    pointer-events: none;
}

/* Contextual figure explainers in the sidebar — always visible. */
.fig-explainer {
    padding: 1rem 1.1rem;
    margin-bottom: 1rem;
    background: var(--bg);
    border: 1px solid var(--hairline);
    border-radius: 8px;
    font-size: 0.92rem;
    line-height: 1.55;
}
.fig-explainer h3 {
    margin: 0 0 0.6rem;
    font-size: 1.05rem;
    color: var(--accent);
}
.fig-explainer p { margin: 0 0 0.6rem; }
.fig-explainer p:last-child { margin-bottom: 0; }
.fig-explainer code {
    background: rgba(0, 0, 0, 0.06);
    padding: 0 0.25em;
    border-radius: 3px;
    font-size: 0.92em;
}
.viz-dnn-canvas-wrap canvas {
    display: block;
    width: 100%;
    height: auto;
    cursor: crosshair;
    touch-action: none;
}
.viz-dnn-math {
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 10px;
    padding: 0.85rem 1.1rem;
    font-family: var(--font-mono);
    font-size: 0.85rem;
    color: var(--ink);
    line-height: 1.7;
    overflow-x: auto;
}
.viz-dnn-math .lbl {
    font-family: var(--font-sans);
    font-size: 0.72rem;
    font-weight: 600;
    letter-spacing: 0.12em;
    text-transform: uppercase;
    color: var(--muted);
    margin-right: 0.5rem;
}
.viz-dnn-math .sum { color: var(--accent); font-weight: 600; }

/* DNN "Inside a layer" viz controls */
.viz-dnn .viz-embed-controls {
    display: inline-flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 0.4rem 1rem;
    font-family: var(--font-sans);
    font-size: 0.85rem;
}
.viz-dnn .viz-embed-controls label {
    display: inline-flex;
    align-items: center;
    gap: 0.3rem;
    cursor: pointer;
}
.viz-dnn .viz-embed-controls input[type="radio"] { accent-color: var(--accent); }
.viz-dnn-label {
    font-weight: 600;
    color: var(--muted);
    font-size: 0.78rem;
    text-transform: uppercase;
    letter-spacing: 0.08em;
}
.viz-dnn-inputs {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 0.45rem 1rem;
    margin-bottom: 0.85rem;
    font-family: var(--font-sans);
    font-size: 0.88rem;
    color: var(--ink-soft);
}
.viz-dnn-inputs label {
    display: inline-flex;
    align-items: center;
    gap: 0.4rem;
}
.viz-dnn-inputs input[type="range"] { width: 160px; accent-color: var(--accent); }
.viz-dnn-readout {
    font-family: var(--font-mono);
    font-size: 0.85rem;
    color: var(--ink);
    min-width: 2.5em;
    display: inline-block;
}
.viz-dnn-arch {
    display: inline-flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 0.4rem;
    margin-top: 0.85rem;
    font-family: var(--font-sans);
    font-size: 0.88rem;
}
.viz-dnn-arch button {
    padding: 0.2rem 0.6rem;
    font-size: 0.85rem;
    background: var(--surface);
    border: 1px solid var(--hairline);
    border-radius: 4px;
    color: var(--ink);
    cursor: pointer;
}
.viz-dnn-arch button:hover { border-color: var(--accent); color: var(--accent); }
.viz-dnn-arch button:disabled { opacity: 0.35; cursor: not-allowed; }

.viz-dnn-explain {
    margin-top: 0.85rem;
    font-family: var(--font-sans);
    font-size: 0.9rem;
    color: var(--ink-soft);
}
.viz-dnn-explain summary {
    cursor: pointer;
    padding: 0.5rem 0.75rem;
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 6px;
    color: var(--accent-hover);
    font-weight: 500;
    user-select: none;
    list-style: none;            /* hide default ▶︎ marker */
}
.viz-dnn-explain summary::-webkit-details-marker { display: none; }
.viz-dnn-explain summary::before {
    content: "▸";
    display: inline-block;
    margin-right: 0.5rem;
    transition: transform 0.15s ease;
}
.viz-dnn-explain[open] summary::before { transform: rotate(90deg); }
.viz-dnn-explain summary:hover { border-color: var(--accent); }
.viz-dnn-explain-body {
    padding: 0.85rem 1.1rem;
    background: rgba(79, 70, 229, 0.04);
    border: 1px solid rgba(79, 70, 229, 0.15);
    border-top: none;
    border-radius: 0 0 6px 6px;
    margin-top: -1px;
    line-height: 1.6;
}
.viz-dnn-explain-body ul { margin: 0; padding-left: 1.1rem; }
.viz-dnn-explain-body li { margin: 0.35rem 0; }


/* RNN recurrence viz — sequence unrolled across timesteps */
.viz-rnn {
    padding: 1.25rem 1.5rem 1.5rem;
}
.viz-rnn-controls {
    display: flex;
    gap: 0.45rem;
    flex-wrap: wrap;
    margin-bottom: 0.85rem;
}
.viz-rnn-controls select,
.viz-rnn-controls button {
    padding: 0.35rem 0.85rem;
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 6px;
    color: var(--ink);
    font-family: var(--font-sans);
    font-size: 0.82rem;
    font-weight: 500;
    cursor: pointer;
    transition: background 0.18s ease, border-color 0.18s ease, color 0.18s ease;
}
.viz-rnn-controls button:hover,
.viz-rnn-controls select:hover {
    background: var(--accent-soft);
    border-color: var(--accent);
    color: var(--accent-hover);
}
.viz-rnn-canvas-wrap {
    background: var(--bg);
    border-radius: 8px;
    padding: 0.5rem;
    margin-bottom: 1rem;
}
.viz-rnn-canvas-wrap canvas {
    display: block;
    width: 100%;
    height: auto;
    cursor: pointer;
    touch-action: none;
}
.viz-rnn-formula {
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 10px;
    padding: 0.85rem 1.1rem;
    font-family: var(--font-mono);
    font-size: 0.88rem;
    color: var(--ink);
    line-height: 1.7;
    overflow-x: auto;
}
.viz-rnn-formula .lbl {
    font-family: var(--font-sans);
    font-size: 0.72rem;
    font-weight: 600;
    letter-spacing: 0.12em;
    text-transform: uppercase;
    color: var(--muted);
    margin-right: 0.5rem;
}
.viz-rnn-formula .sum { color: var(--accent); font-weight: 600; }


/* Autoencoder viz — input image, encoder neck, 2D latent, decoder neck, output */
.viz-ae { padding: 1.25rem 1.5rem 1.5rem; }
.viz-ae-controls {
    display: flex;
    gap: 0.55rem;
    flex-wrap: wrap;
    align-items: center;
    margin-bottom: 0.85rem;
}
.viz-ae-presets {
    display: inline-flex;
    gap: 0.35rem;
    flex-wrap: wrap;
}
.viz-ae-chip {
    padding: 0.32rem 0.78rem;
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 999px;
    color: var(--ink);
    font-family: var(--font-sans);
    font-size: 0.8rem;
    font-weight: 500;
    cursor: pointer;
    transition: background 0.15s ease, border-color 0.15s ease, color 0.15s ease;
}
.viz-ae-chip:hover {
    border-color: var(--accent);
    color: var(--accent-hover);
}
.viz-ae-chip.active {
    background: var(--accent-warm);
    border-color: var(--accent-warm);
    color: #ffffff;
}
.viz-ae-controls button:not(.viz-ae-chip) {
    padding: 0.32rem 0.78rem;
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 6px;
    color: var(--ink);
    font-family: var(--font-sans);
    font-size: 0.8rem;
    font-weight: 500;
    cursor: pointer;
    transition: background 0.15s ease, border-color 0.15s ease, color 0.15s ease;
}
.viz-ae-controls button:not(.viz-ae-chip):hover {
    background: var(--accent-soft);
    border-color: var(--accent);
    color: var(--accent-hover);
}
.viz-ae-controls button.active:not(.viz-ae-chip) {
    background: var(--accent-soft);
    border-color: var(--accent);
    color: var(--accent-hover);
}
.viz-ae-canvas-wrap {
    background: var(--bg);
    border-radius: 8px;
    padding: 0.5rem;
    margin-bottom: 1rem;
}
.viz-ae-canvas-wrap canvas {
    display: block;
    width: 100%;
    height: auto;
    cursor: crosshair;
    touch-action: none;
}
.viz-ae-caption {
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 10px;
    padding: 0.85rem 1.1rem;
    font-size: 0.9rem;
    color: var(--ink-soft);
    line-height: 1.55;
}
.viz-ae-caption strong { color: var(--accent-hover); }


/* GAN training viz — real vs fake scatter, D heatmap, loss curves */
.viz-gan { padding: 1.25rem 1.5rem 1.5rem; }
.viz-gan-controls {
    display: flex;
    gap: 0.45rem;
    flex-wrap: wrap;
    align-items: center;
    margin-bottom: 0.85rem;
}
.viz-gan-controls button,
.viz-gan-controls select {
    padding: 0.35rem 0.85rem;
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 6px;
    color: var(--ink);
    font-family: var(--font-sans);
    font-size: 0.82rem;
    font-weight: 500;
    cursor: pointer;
    transition: background 0.15s ease, border-color 0.15s ease, color 0.15s ease;
}
.viz-gan-controls button:hover,
.viz-gan-controls select:hover {
    background: var(--accent-soft);
    border-color: var(--accent);
    color: var(--accent-hover);
}
.viz-gan-counter {
    margin-left: auto;
    padding: 0.25rem 0.7rem;
    background: var(--accent-soft);
    color: var(--accent-hover);
    border-radius: 999px;
    font-family: var(--font-mono);
    font-size: 0.82rem;
    font-weight: 600;
}
.viz-gan-canvas-wrap {
    background: var(--bg);
    border-radius: 8px;
    padding: 0.5rem;
    margin-bottom: 1rem;
}
.viz-gan-canvas-wrap canvas {
    display: block;
    width: 100%;
    height: auto;
    touch-action: none;
}
.viz-gan-caption {
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 10px;
    padding: 0.85rem 1.1rem;
    font-size: 0.9rem;
    color: var(--ink-soft);
    line-height: 1.55;
}
.viz-gan-caption strong { color: var(--accent-hover); }


/* Diffusion viz — timeline strip, big x_t / predicted x_0 / predicted noise */
.viz-diff { padding: 1.25rem 1.5rem 1.5rem; }
.viz-diff-controls {
    display: flex;
    gap: 0.5rem;
    flex-wrap: wrap;
    align-items: center;
    margin-bottom: 0.85rem;
}
.viz-diff-controls button,
.viz-diff-controls select {
    padding: 0.35rem 0.85rem;
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 6px;
    color: var(--ink);
    font-family: var(--font-sans);
    font-size: 0.82rem;
    font-weight: 500;
    cursor: pointer;
    transition: background 0.15s ease, border-color 0.15s ease, color 0.15s ease;
}
.viz-diff-controls button:hover,
.viz-diff-controls select:hover {
    background: var(--accent-soft);
    border-color: var(--accent);
    color: var(--accent-hover);
}
.viz-diff-slider {
    flex: 1;
    min-width: 160px;
    accent-color: var(--accent-warm);
    cursor: pointer;
}
.viz-diff-t {
    padding: 0.25rem 0.7rem;
    background: var(--accent-soft);
    color: var(--accent-hover);
    border-radius: 999px;
    font-family: var(--font-mono);
    font-size: 0.82rem;
    font-weight: 600;
    min-width: 4.5em;
    text-align: center;
}
.viz-diff-canvas-wrap {
    background: var(--bg);
    border-radius: 8px;
    padding: 0.5rem;
    margin-bottom: 1rem;
}
.viz-diff-canvas-wrap canvas {
    display: block;
    width: 100%;
    height: auto;
    touch-action: none;
}
.viz-diff-caption {
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 10px;
    padding: 0.85rem 1.1rem;
    font-size: 0.9rem;
    color: var(--ink-soft);
    line-height: 1.55;
}
.viz-diff-caption strong { color: var(--accent-hover); }


/* Shared "non-NN" viz shell — k-means, trees, SVM, GMM, GP, etc. */
.viz-classic { padding: 1.25rem 1.5rem 1.5rem; }
.viz-classic-controls {
    display: flex;
    gap: 0.45rem;
    flex-wrap: wrap;
    align-items: center;
    margin-bottom: 0.85rem;
}
.viz-classic-controls button,
.viz-classic-controls select {
    padding: 0.35rem 0.85rem;
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 6px;
    color: var(--ink);
    font-family: var(--font-sans);
    font-size: 0.82rem;
    font-weight: 500;
    cursor: pointer;
    transition: background 0.15s ease, border-color 0.15s ease, color 0.15s ease;
}
.viz-classic-controls button:hover,
.viz-classic-controls select:hover {
    background: var(--accent-soft);
    border-color: var(--accent);
    color: var(--accent-hover);
}
.viz-classic-controls button.active {
    background: var(--accent-soft);
    border-color: var(--accent);
    color: var(--accent-hover);
}
.viz-classic-badge {
    margin-left: auto;
    padding: 0.25rem 0.7rem;
    background: var(--accent-soft);
    color: var(--accent-hover);
    border-radius: 999px;
    font-family: var(--font-mono);
    font-size: 0.82rem;
    font-weight: 600;
}
.viz-classic-slider {
    flex: 0 1 180px;
    min-width: 120px;
    accent-color: var(--accent-warm);
    cursor: pointer;
}
.viz-classic-canvas-wrap {
    background: var(--bg);
    border-radius: 8px;
    padding: 0.5rem;
    margin-bottom: 1rem;
}
.viz-classic-canvas-wrap canvas {
    display: block;
    width: 100%;
    height: auto;
    touch-action: none;
}
.viz-classic-caption {
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 10px;
    padding: 0.85rem 1.1rem;
    font-size: 0.9rem;
    color: var(--ink-soft);
    line-height: 1.55;
}
.viz-classic-caption strong { color: var(--accent-hover); }


/* Transformer attention viz — heads as tabs, arcs above tokens, heatmap below */
.viz-tx {
    padding: 1.25rem 1.5rem 1.5rem;
}
.viz-tx-heads {
    display: flex;
    flex-wrap: wrap;
    gap: 0.4rem;
    margin-bottom: 1rem;
}
.viz-tx-head {
    padding: 0.4rem 0.85rem;
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 999px;
    color: var(--ink-soft);
    font-family: var(--font-sans);
    font-size: 0.85rem;
    font-weight: 500;
    cursor: pointer;
    transition: background 0.18s ease, border-color 0.18s ease, color 0.18s ease;
}
.viz-tx-head:hover {
    background: var(--accent-soft);
    border-color: var(--accent);
    color: var(--accent-hover);
}
.viz-tx-head.active {
    background: var(--accent);
    border-color: var(--accent);
    color: var(--white);
}
.viz-tx-canvas-wrap {
    background: var(--bg);
    border-radius: 8px;
    padding: 0.5rem;
    margin-bottom: 1rem;
}
.viz-tx-canvas-wrap canvas {
    display: block;
    width: 100%;
    height: auto;
    cursor: pointer;
    touch-action: none;
}
.viz-tx-desc {
    background: var(--accent-soft);
    border: 1px solid rgba(79, 70, 229, 0.16);
    border-radius: 10px;
    padding: 0.85rem 1.1rem;
    font-size: 0.93rem;
    color: var(--ink-soft);
    line-height: 1.55;
}
.viz-tx-desc strong { color: var(--accent-hover); }


/* CNN convolution viz — three-panel layout (input / kernel+math / output) */
.viz-cnn { padding: 1.5rem; }

/* Controls bar above the three-panel layout */
.viz-cnn-controls {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 0.75rem 1rem;
    padding: 0.75rem 0 1rem;
    margin-bottom: 1rem;
    border-bottom: 1px solid var(--hairline);
}
.viz-cnn-label-inline {
    display: inline-flex;
    align-items: center;
    gap: 0.4rem;
    color: var(--muted);
    font-size: 0.85rem;
}
.viz-cnn-label-inline select {
    font-size: 0.85rem;
    padding: 0.25rem 0.4rem;
}
.viz-cnn-mode-toggle {
    display: inline-flex;
    border: 1px solid var(--hairline);
    border-radius: 6px;
    overflow: hidden;
}
.viz-cnn-mode-toggle button {
    background: none;
    border: none;
    padding: 0.4rem 0.85rem;
    cursor: pointer;
    font-size: 0.85rem;
    color: var(--muted);
    font-family: inherit;
}
.viz-cnn-mode-toggle button.active {
    background: var(--accent);
    color: #fff;
}
.viz-cnn-mode-pane {
    display: inline-flex;
    align-items: center;
    gap: 0.55rem;
    margin-left: auto;
}
.viz-cnn-mode-pane[hidden] { display: none; }
.viz-cnn-mode-pane button {
    background: var(--bg);
    border: 1px solid var(--hairline);
    border-radius: 5px;
    padding: 0.32rem 0.7rem;
    cursor: pointer;
    font-size: 0.85rem;
    color: var(--ink);
    font-family: inherit;
}
.viz-cnn-mode-pane button:hover { border-color: var(--accent); color: var(--accent); }
.viz-cnn-mode-pane button.viz-cnn-primary {
    background: var(--accent);
    color: #fff;
    border-color: var(--accent);
    font-weight: 600;
}
.viz-cnn-mode-pane button.viz-cnn-primary:hover {
    background: var(--accent-hover);
    border-color: var(--accent-hover);
    color: #fff;
}

/* Pooling section — sits below the conv viz */
.viz-cnn-pool {
    margin-top: 1.5rem;
    padding-top: 1.25rem;
    border-top: 1px solid var(--hairline);
}
.viz-cnn-pool-header {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 0.75rem 1rem;
    margin-bottom: 1rem;
}
.viz-cnn-pool-title {
    flex: 1;
    color: var(--ink-soft);
    font-size: 0.92rem;
    line-height: 1.5;
    min-width: 280px;
}
.viz-cnn-pool-title strong { color: var(--ink); }
.viz-cnn-pool-layout {
    display: grid;
    grid-template-columns: auto auto auto;
    gap: 1.25rem;
    align-items: center;
    justify-content: center;
}
.viz-cnn-pool-arrow {
    font-size: 1.8rem;
    color: var(--muted);
    align-self: center;
    padding: 0 0.5rem;
}
.viz-cnn-pool canvas { cursor: crosshair; }

/* Three-panel main row: input | kernel | output */
.viz-cnn-layout {
    display: grid;
    grid-template-columns: auto auto auto;
    gap: 1.5rem;
    align-items: start;
    justify-content: center;
}
.viz-cnn-panel {
    display: flex;
    flex-direction: column;
    align-items: center;
}
.viz-cnn-label {
    font-family: var(--font-sans);
    font-size: 0.72rem;
    font-weight: 600;
    letter-spacing: 0.12em;
    text-transform: uppercase;
    color: var(--muted);
    margin-bottom: 0.5rem;
}
.viz-cnn-sub {
    font-size: 0.78rem;
    color: var(--muted);
    margin-top: 0.45rem;
    text-align: center;
    max-width: 260px;
    line-height: 1.4;
}
.viz-cnn-panel canvas {
    display: block;
    background: var(--bg);
    border-radius: 6px;
    cursor: crosshair;
    image-rendering: pixelated;
    touch-action: none;
}

/* Learn-mode extra row: target feature map + loss curve */
.viz-cnn-learn-row {
    display: grid;
    grid-template-columns: auto 1fr;
    gap: 1.5rem;
    align-items: start;
    padding-top: 1.25rem;
    margin-top: 1.25rem;
    border-top: 1px solid var(--hairline);
}
.viz-cnn-learn-row[hidden] { display: none; }
.viz-cnn-loss-panel {
    display: flex;
    flex-direction: column;
    min-width: 0;
}
.viz-cnn-loss-panel canvas {
    display: block;
    width: 100%;
    background: var(--bg);
    border-radius: 6px;
}
.viz-cnn-readout {
    font-family: var(--font-mono, ui-monospace), monospace;
    font-size: 0.85rem;
    color: var(--ink);
    margin-top: 0.5rem;
    font-weight: 600;
}

@media (max-width: 720px) {
    .viz-cnn-layout      { grid-template-columns: 1fr; }
    .viz-cnn-learn-row   { grid-template-columns: 1fr; }
    .viz-cnn-mode-pane   { margin-left: 0; width: 100%; flex-wrap: wrap; }
    .viz-cnn-pool-layout { grid-template-columns: 1fr; }
    .viz-cnn-pool-arrow  { transform: rotate(90deg); }
}


/* Embedded interactive viz — a canvas widget at the top of a Visual tab */
.viz-embed {
    margin: 0 0 1.75rem;
    padding: 1.25rem;
    background: var(--surface);
    border: 1px solid var(--hairline);
    border-radius: 12px;
    box-shadow: 0 4px 16px -10px rgba(26, 26, 26, 0.1);
}
.viz-embed-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 1rem;
    flex-wrap: wrap;
    margin-bottom: 0.85rem;
}
.viz-embed-title {
    font-family: var(--font-sans);
    font-size: 0.88rem;
    color: var(--muted);
}
.viz-embed-title kbd {
    font-family: var(--font-mono);
    font-size: 0.75rem;
    padding: 0.05rem 0.4rem;
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 4px;
    color: var(--ink);
    margin: 0 0.15rem;
}
.viz-embed-controls {
    display: flex;
    gap: 0.45rem;
}
.viz-embed-controls button {
    padding: 0.35rem 0.85rem;
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 6px;
    color: var(--ink);
    font-family: var(--font-sans);
    font-size: 0.82rem;
    font-weight: 500;
    cursor: pointer;
    transition: background 0.18s ease, border-color 0.18s ease, color 0.18s ease;
}
.viz-embed-controls button:hover {
    background: var(--accent-soft);
    border-color: var(--accent);
    color: var(--accent-hover);
}
.viz-embed canvas {
    display: block;
    width: 100%;
    height: auto;
    border-radius: 8px;
    background: var(--bg);
    cursor: crosshair;
    touch-action: none;
}
.viz-embed-stats {
    display: flex;
    gap: 1.5rem;
    margin-top: 0.85rem;
    padding-top: 0.85rem;
    border-top: 1px solid var(--hairline);
    font-family: var(--font-mono);
    font-size: 0.92rem;
    color: var(--ink);
    flex-wrap: wrap;
}
.viz-embed-stats > span {
    display: inline-flex;
    align-items: baseline;
    gap: 0.35rem;
}
.viz-embed-stats .label {
    font-family: var(--font-sans);
    font-size: 0.78rem;
    font-weight: 600;
    color: var(--muted);
    text-transform: uppercase;
    letter-spacing: 0.08em;
}


/* Visual-intuition level — grid of curated interactive explainers */
.viz-intro {
    color: var(--muted);
    font-size: 1rem;
    line-height: 1.6;
    margin: 0 0 1.5rem;
    max-width: 660px;
}
.viz-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 1.25rem;
    margin-bottom: 2rem;
}
.viz-card {
    display: flex;
    flex-direction: column;
    padding: 1.5rem;
    background: var(--surface);
    border: 1px solid var(--hairline);
    border-radius: 12px;
    text-decoration: none;
    color: var(--ink);
    transition: transform 0.25s ease, border-color 0.25s ease, box-shadow 0.25s ease;
    position: relative;
    overflow: hidden;
}
.viz-card:hover {
    transform: translateY(-3px);
    border-color: var(--accent);
    box-shadow: 0 10px 24px -12px rgba(79, 70, 229, 0.22);
}
.viz-card.viz-card-featured {
    background: linear-gradient(135deg, var(--surface), var(--accent-soft));
    border-color: rgba(79, 70, 229, 0.22);
}
.viz-card .viz-source {
    display: inline-block;
    font-family: var(--font-mono);
    font-size: 0.72rem;
    color: var(--muted);
    margin-bottom: 0.5rem;
    letter-spacing: 0.02em;
}
.viz-card h3 {
    font-family: var(--font-serif);
    font-size: 1.18rem;
    font-weight: 500;
    color: var(--ink);
    margin: 0 0 0.6rem;
}
.viz-card p {
    color: var(--ink-soft);
    font-size: 0.93rem;
    line-height: 1.55;
    margin: 0 0 0.85rem;
    flex-grow: 1;
}
.viz-card .viz-cta {
    display: inline-flex;
    align-items: center;
    gap: 0.4rem;
    color: var(--accent);
    font-size: 0.88rem;
    font-weight: 600;
    transition: gap 0.2s ease;
}
.viz-card:hover .viz-cta { gap: 0.6rem; }
.viz-card .viz-cta i { font-size: 0.78em; }


/* Footer callout per level: suggest the next level up (or down) */
.level-next {
    margin: 2.5rem 0 0;
    padding: 0.85rem 1.1rem;
    background: var(--accent-soft);
    border: 1px solid rgba(79, 70, 229, 0.16);
    border-radius: 10px;
    font-size: 0.92rem;
    color: var(--accent-hover);
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem 1rem;
    align-items: center;
}
.level-next button {
    background: transparent;
    border: none;
    color: var(--accent-hover);
    font-family: inherit;
    font-size: inherit;
    font-weight: 600;
    cursor: pointer;
    padding: 0;
    text-decoration: underline;
    text-underline-offset: 3px;
    transition: color 0.2s ease;
}
.level-next button:hover { color: var(--accent); }

/* Annotated formula: math + a labelled legend underneath */
.formula-block .formula {
    display: block;
    font-family: var(--font-mono);
    font-size: 1rem;
    color: var(--ink);
    padding: 0.5rem 0 0.85rem;
    overflow-x: auto;
}
/* KaTeX overrides: collapse its own outer margins, allow horizontal scroll */
.formula-block .formula .katex-display {
    margin: 0.2rem 0 0.4rem;
    overflow-x: auto;
    overflow-y: hidden;
    padding-bottom: 0.25rem;  /* room for scroll bar */
}
.formula-block .formula .katex { font-size: 1.05em; }
.formula-legend {
    list-style: none;
    padding: 0;
    margin: 0;
    border-top: 1px solid rgba(79, 70, 229, 0.18);
    padding-top: 0.75rem;
}
.formula-legend li {
    margin: 0.25rem 0;
    font-size: 0.88rem;
    color: var(--ink-soft);
    line-height: 1.5;
}
.formula-legend code {
    background: rgba(255, 255, 255, 0.55);
    color: var(--accent-hover);
    padding: 0.05rem 0.4rem;
    border-radius: 4px;
    font-size: 0.85rem;
    margin-right: 0.4rem;
    min-width: 2.5em;
    display: inline-block;
    text-align: center;
}

@media (max-width: 900px) {
    .topic-layout {
        grid-template-columns: 1fr;
        gap: 1.5rem;
    }
    .topic-sidebar { position: static; }
    .learn-more { margin-top: 0; }
}

/* Eyebrow as a breadcrumb-style back-link */
a.eyebrow {
    text-decoration: none;
    transition: background 0.2s ease;
}
a.eyebrow:hover {
    background: var(--accent);
    color: var(--white);
}

/* TL;DR body: short and tight */
.tldr-body p {
    margin: 0 0 1rem;
    line-height: 1.7;
    color: var(--ink-soft);
    font-size: 1.02rem;
}
.tldr-body p:last-child { margin-bottom: 0; }
.tldr-body strong { color: var(--ink); }
.tldr-body h3 {
    margin: 1.6rem 0 0.6rem;
    font-size: 1.08rem;
    color: var(--accent);
    font-weight: 600;
}
.tldr-body h3:first-child { margin-top: 0; }
.tldr-body ul {
    margin: 0.4rem 0 1rem 0;
    padding-left: 1.2rem;
    color: var(--ink-soft);
    font-size: 1.02rem;
    line-height: 1.6;
}
.tldr-body ul li { margin-bottom: 0.35rem; }
.tldr-body a {
    color: var(--accent);
    text-decoration: none;
    border-bottom: 1px dotted currentColor;
}
.tldr-body a:hover { color: var(--accent-hover); }

/* Key-idea callout: holds the core formula / one-sentence intuition */
.key-idea {
    background: linear-gradient(135deg, var(--accent-soft), var(--accent-warm-soft));
    border: 1px solid rgba(79, 70, 229, 0.18);
    border-radius: 12px;
    padding: 1.4rem 1.6rem;
    margin: 2rem 0;
}
.key-idea-label {
    display: block;
    font-family: var(--font-sans);
    font-size: 0.68rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.16em;
    color: var(--accent-hover);
    margin-bottom: 0.55rem;
}
.key-idea p {
    margin: 0;
    color: var(--ink);
    font-size: 1.02rem;
    line-height: 1.6;
}
.key-idea .formula {
    display: block;
    font-family: var(--font-mono);
    font-size: 0.95rem;
    color: var(--ink);
    padding: 0.4rem 0 0.6rem;
    overflow-x: auto;
}

/* When-to-use / when-to-avoid split box */
.use-cases {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 0;
    margin: 2rem 0;
    border: 1px solid var(--hairline);
    border-radius: 12px;
    overflow: hidden;
}
.use-cases > div { padding: 1.2rem 1.4rem; }
.use-cases .yes {
    background: var(--surface);
    border-right: 1px solid var(--hairline);
}
.use-cases .no { background: var(--light-bg); }
.use-cases h3 {
    font-family: var(--font-sans);
    font-size: 0.7rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.14em;
    margin: 0 0 0.75rem;
}
.use-cases .yes h3 { color: #2d8a5a; }
.use-cases .no h3 { color: var(--muted); }
.use-cases ul { list-style: none; padding: 0; margin: 0; }
.use-cases li {
    padding: 0.3rem 0 0.3rem 1.35rem;
    color: var(--ink-soft);
    font-size: 0.93rem;
    line-height: 1.45;
    position: relative;
}
.use-cases .yes li::before {
    content: '✓';
    position: absolute;
    left: 0;
    color: #2d8a5a;
    font-weight: 600;
}
.use-cases .no li::before {
    content: '✗';
    position: absolute;
    left: 0;
    color: var(--muted);
    font-weight: 600;
}

/* Neutral variant — for topics where the two columns aren't pro/con
   (e.g., bias-variance "two failure modes"). Bullets instead of ✓/✗. */
.use-cases.neutral .yes h3,
.use-cases.neutral .no h3 { color: var(--ink); }
.use-cases.neutral li::before {
    content: '•';
    color: var(--accent-warm);
    font-size: 1.2em;
    line-height: 1;
    top: 0.15em;
}

/* Code snippet with copy button */
.code-snippet {
    position: relative;
    margin: 2rem 0;
}
.code-snippet pre {
    background: #1a1a1a;
    color: #e8e8e8;
    padding: 1.25rem 1.5rem;
    border-radius: 10px;
    overflow-x: auto;
    font-size: 0.85rem;
    line-height: 1.6;
    margin: 0;
}
.code-snippet code { font-family: var(--font-mono); }
.copy-btn {
    position: absolute;
    top: 0.65rem;
    right: 0.65rem;
    background: rgba(255, 255, 255, 0.06);
    border: 1px solid rgba(255, 255, 255, 0.15);
    color: #b0b0b0;
    padding: 0.3rem 0.7rem;
    font-size: 0.7rem;
    font-family: var(--font-sans);
    font-weight: 500;
    border-radius: 6px;
    cursor: pointer;
    transition: all 0.2s ease;
    letter-spacing: 0.04em;
}
.copy-btn:hover {
    background: rgba(255, 255, 255, 0.12);
    color: #ffffff;
}
.copy-btn.copied {
    background: rgba(79, 70, 229, 0.3);
    border-color: rgba(79, 70, 229, 0.5);
    color: #ffffff;
}

/* "Where to learn more" reading-list box with annotations */
.learn-more {
    margin: 3rem 0 2rem;
    padding: 1.5rem 1.75rem;
    background: var(--light-bg);
    border: 1px solid var(--hairline);
    border-radius: 12px;
}
.learn-more h3 {
    font-family: var(--font-sans);
    font-size: 0.7rem;
    font-weight: 600;
    letter-spacing: 0.14em;
    text-transform: uppercase;
    color: var(--accent);
    margin-bottom: 0.9rem;
}
.learn-more ul { list-style: none; padding: 0; margin: 0; }
.learn-more li {
    padding: 0.7rem 0;
    border-bottom: 1px solid var(--hairline);
    font-size: 0.95rem;
    line-height: 1.45;
}
.learn-more li:last-child { border-bottom: none; }
.learn-more a {
    color: var(--ink);
    text-decoration: none;
    display: inline-flex;
    align-items: baseline;
    gap: 0.35rem;
    font-weight: 500;
}
.learn-more a:hover { color: var(--accent); }
.learn-more a i {
    font-size: 0.7em;
    color: var(--muted);
    transition: color 0.2s ease;
}
.learn-more a:hover i { color: var(--accent); }
.learn-more .annotation {
    display: block;
    color: var(--muted);
    font-size: 0.88rem;
    margin-top: 0.15rem;
    line-height: 1.5;
}

@media (max-width: 600px) {
    .use-cases { grid-template-columns: 1fr; }
    .use-cases .yes { border-right: none; border-bottom: 1px solid var(--hairline); }
}

/* Prev/next navigation between sibling topics */
.topic-nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 1rem;
    margin-top: 3rem;
    padding-top: 1.5rem;
    border-top: 1px solid var(--hairline);
    font-size: 0.9rem;
}
.topic-nav a {
    color: var(--muted);
    display: inline-flex;
    align-items: center;
    gap: 0.4rem;
    transition: color 0.2s ease;
    max-width: 45%;
}
.topic-nav a:hover { color: var(--accent); }
.topic-nav .topic-nav-label {
    display: block;
    font-size: 0.72rem;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--muted);
    margin-bottom: 0.15rem;
}
.topic-nav .topic-nav-title { color: var(--ink); font-weight: 500; }
.topic-nav a:hover .topic-nav-title { color: var(--accent); }
.topic-nav .prev { text-align: left; }
.topic-nav .next { text-align: right; margin-left: auto; }


/* ---------- Responsive ---------- */
@media (max-width: 768px) {
    .nav-links { display: none; }
    .nav-toggle { display: block; }
    .navbar { padding: 0.85rem 1.25rem; }

    .hero { min-height: 50vh; padding: 4rem 1.25rem 3rem; }
    .hero-content h1 { font-size: 2.2rem; }

    .container { margin: 2.5rem auto; }

    .concept-grid, .component-grid, .resource-grid, .topic-grid {
        grid-template-columns: 1fr;
    }
    .content-section { padding: 1.5rem; }
    .code-example { padding: 1rem; }

    .footer-content {
        flex-direction: column;
        gap: 1rem;
        text-align: center;
    }
    .social-links { margin-top: 0.25rem; }
    .social-links a { margin: 0 0.5rem; }
}