/* ============================================================
   book.css - AI-Powered Products Book Stylesheet
   Aligned with LLMBook reference design
   ============================================================ */

/* ----- :root variables ----- */
:root {
    --primary: #1a1a2e;
    --accent: #0f3460;
    --highlight: #e94560;
    --bg: #fafafa;
    --text: #2d3436;
    --text-light: #555;
    --code-bg: #1e1e2e;
    --code-text: #cdd6f4;
}

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

/* ----- Base typography ----- */
body {
    font-family: 'Georgia', 'Times New Roman', serif;
    background: var(--bg);
    color: var(--text);
    line-height: 1.85;
    font-size: 17px;
    -webkit-hyphens: auto;
    hyphens: auto;
}

p {
    margin-bottom: 1.2rem;
    text-align: justify;
}

a { color: var(--accent); text-decoration: none; }
a:hover { color: var(--highlight); }

/* Visible link cues inside content areas */
.content a:not(.section-card):not(.toc-link):not(.book-title-link):not(.toc-part-header):not(.toc-ch) {
    color: #1a6fb5;
    text-decoration: underline;
    text-decoration-color: rgba(26, 111, 181, 0.4);
    text-underline-offset: 2px;
    text-decoration-thickness: 1.5px;
    transition: text-decoration-color 0.2s, color 0.2s;
}
.content a:not(.section-card):not(.toc-link):not(.book-title-link):not(.toc-part-header):not(.toc-ch):hover {
    color: var(--highlight);
    text-decoration-color: var(--highlight);
    text-decoration-thickness: 2px;
}
.chapter-nav a { text-decoration: none !important; }

ul, ol { margin: 0.5rem 0 1.2rem 1.5rem; }
li { margin-bottom: 0.4rem; }

/* ----- Headings ----- */
h2 {
    font-size: 1.8rem;
    color: var(--primary);
    margin: 3rem 0 1.5rem;
    padding-bottom: 0.5rem;
    border-bottom: 3px solid var(--highlight);
    line-height: 1.3;
}
h3 {
    font-size: 1.35rem;
    color: var(--accent);
    margin: 2rem 0 1rem;
    line-height: 1.3;
}
h4 {
    font-size: 1.1rem;
    color: var(--primary);
    margin: 1.5rem 0 0.75rem;
}

/* ----- Layout: .content ----- */
.content {
    max-width: 820px;
    margin: 0 auto;
    padding: 3rem 2rem;
}

/* ----- Chapter header ----- */
.chapter-header {
    background: linear-gradient(135deg, var(--primary), var(--accent));
    color: white;
    padding: 0 2rem 2rem;
    text-align: center;
}
.chapter-header h1 {
    font-size: 2.2rem;
    font-weight: 700;
    margin-bottom: 0.5rem;
    line-height: 1.2;
}

/* Header navigation bar */
.header-nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.5rem 0.5rem;
    margin: 0 -0.5rem 0.8rem;
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 0.78rem;
    letter-spacing: 0.03em;
}
.header-nav .book-title-link {
    color: rgba(255,255,255,0.65);
    text-decoration: none;
    transition: color 0.2s;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    max-width: 70%;
}
.header-nav .book-title-link:hover { color: rgba(255,255,255,0.95); }
.header-nav .toc-link {
    display: inline-flex;
    align-items: center;
    gap: 0.35rem;
    color: rgba(255,255,255,0.6);
    text-decoration: none;
    font-size: 0.8rem;
    padding: 0.25rem 0.6rem;
    border: 1px solid rgba(255,255,255,0.2);
    border-radius: 4px;
    transition: all 0.2s;
}
.header-nav .toc-link:hover {
    color: rgba(255,255,255,0.95);
    border-color: rgba(255,255,255,0.5);
    background: rgba(255,255,255,0.08);
}
.header-nav .toc-icon {
    font-size: 1rem;
    line-height: 1;
}

/* Header hierarchy */
.part-label {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 0.88rem;
    letter-spacing: 0.05em;
    margin-bottom: 0.15rem;
}
.part-label a {
    color: rgba(255,255,255,0.85);
    text-decoration: none;
}
.part-label a:hover { opacity: 0.9; }

.chapter-label {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 0.8rem;
    text-transform: uppercase;
    letter-spacing: 3px;
    margin-bottom: 0.3rem;
}
.chapter-label a {
    color: rgba(255,255,255,0.7);
    text-decoration: none;
}
.chapter-label a:hover { opacity: 0.9; }

.chapter-header .subtitle,
.chapter-header .chapter-subtitle {
    font-size: 1.1rem;
    opacity: 0.85;
    max-width: 650px;
    margin: 0.5rem auto 0;
    font-style: italic;
    text-align: center;
    line-height: 1.5;
}

/* ----- Epigraph ----- */
.epigraph {
    max-width: 100%;
    margin: 2rem 0 2.5rem;
    padding: 1.2rem 1.5rem;
    border-left: 4px solid var(--highlight);
    background: linear-gradient(135deg, rgba(233,69,96,0.04), rgba(15,52,96,0.04));
    border-radius: 0 8px 8px 0;
    font-style: italic;
    font-size: 1.05rem;
    line-height: 1.6;
    color: var(--text);
}
.epigraph p { margin: 0 0 0.5rem 0; }
.epigraph cite {
    display: flex;
    align-items: center;
    justify-content: flex-end;
    gap: 0.5rem;
    font-style: normal;
    font-size: 0.9rem;
    color: var(--highlight);
    font-weight: 600;
    text-align: right;
}
.epigraph cite::before { content: "\2014\00a0"; }

/* ----- Learning Objectives ----- */
.objectives {
    margin: 1.5rem 0 2rem;
    padding: 1.4rem 1.8rem;
    background: linear-gradient(135deg, #e8f5e9, #f1f8e9);
    border: 1px solid rgba(67,160,71,0.18);
    border-left: 5px solid #43a047;
    border-radius: 0 8px 8px 0;
    font-size: 0.95rem;
    line-height: 1.65;
}
.objectives h3 {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 1.1rem;
    font-weight: 700;
    color: #2e7d32;
    margin: 0 0 0.6rem;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}
.objectives ul { margin: 0.3rem 0 0 1.4rem; }
.objectives li { margin-bottom: 0.35rem; }

/* ----- Chapter Navigation ----- */
.chapter-nav, nav.chapter-nav {
    display: grid;
    grid-template-columns: 1fr auto 1fr;
    gap: 0.75rem;
    max-width: 820px;
    margin: 3rem auto 0;
    padding: 0;
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 0.88rem;
    border-top: none;
}
.chapter-nav a {
    display: flex;
    align-items: center;
    gap: 0.6rem;
    padding: 0.85rem 1.1rem;
    border-radius: 10px;
    text-decoration: none !important;
    font-weight: 600;
    color: var(--accent);
    background: linear-gradient(135deg, #f0f2f5 0%, #e8ecf1 100%);
    border: 1px solid #d8dde4;
    transition: all 0.25s ease;
    line-height: 1.35;
}
.chapter-nav a:hover {
    color: var(--highlight);
    background: linear-gradient(135deg, #fff 0%, #f5f0f2 100%);
    border-color: var(--highlight);
    box-shadow: 0 3px 12px rgba(233, 69, 96, 0.1);
    transform: translateY(-1px);
}
.chapter-nav a.prev::before { content: "\2190"; font-size: 1.15rem; flex-shrink: 0; }
.chapter-nav a.next::after { content: "\2192"; font-size: 1.15rem; flex-shrink: 0; margin-left: auto; }
.chapter-nav a.up, .chapter-nav a:nth-child(2) {
    justify-content: center;
    text-align: center;
    font-size: 0.82rem;
    font-weight: 500;
    background: transparent;
    border-color: transparent;
    color: var(--text-light);
    padding: 0.6rem 0.8rem;
}
.chapter-nav a.up:hover {
    color: var(--accent);
    background: rgba(15, 52, 96, 0.04);
    box-shadow: none;
    transform: none;
}
.chapter-nav a.up::before { content: "\2191"; font-size: 1rem; opacity: 0.5; }
.chapter-nav a.next, .chapter-nav a:last-child:not(.up):not(.prev) { justify-content: flex-end; text-align: right; }

/* ----- Callout boxes (11 canonical types) ----- */
.callout {
    border: 1px solid;
    border-left: 5px solid;
    padding: 1.2rem 1.5rem;
    margin: 1.5rem 0;
    border-radius: 0 8px 8px 0;
}
.callout-title {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-weight: 700;
    font-size: 0.95rem;
    letter-spacing: 0.3px;
    margin-bottom: 0.5rem;
    cursor: help;
    position: relative;
}

/* Tooltip descriptions (single source of truth, pure CSS) */
.callout .callout-title::after {
    position: absolute;
    left: 0;
    top: 100%;
    background: #333;
    color: white;
    padding: 6px 12px;
    border-radius: 4px;
    font-size: 0.75rem;
    font-weight: normal;
    font-style: normal;
    text-transform: none;
    letter-spacing: 0;
    white-space: normal;
    max-width: 320px;
    line-height: 1.4;
    z-index: 100;
    margin-top: 4px;
    box-shadow: 0 2px 8px rgba(0,0,0,0.15);
    opacity: 0;
    pointer-events: none;
    transition: opacity 0.2s ease;
}
.callout .callout-title:hover::after { opacity: 1; }

/* Tooltip text per callout type */
.callout.big-picture .callout-title::after {
    content: "Sets the context: why this topic matters and how it connects to the broader picture.";
}
.callout.key-insight .callout-title::after {
    content: "A core concept or mental model worth remembering. This is one of the section's main takeaways.";
}
.callout.note .callout-title::after {
    content: "Additional detail or clarification that supplements the main text.";
}
.callout.warning .callout-title::after {
    content: "A common mistake, pitfall, or misconception to watch out for.";
}
.callout.practical-example .callout-title::after {
    content: "A real-world scenario showing how practitioners apply this concept in production.";
}
.callout.fun-note .callout-title::after {
    content: "A lighthearted or surprising fact related to the topic. Not essential, but memorable.";
}
.callout.research-frontier .callout-title::after {
    content: "Current research directions and open questions at the cutting edge of this field.";
}
.callout.algorithm .callout-title::after {
    content: "Step-by-step pseudocode or formal procedure for an algorithm discussed in this section.";
}
.callout.tip .callout-title::after {
    content: "A practical shortcut, best practice, or time-saving technique from experienced practitioners.";
}
.callout.exercise .callout-title::after {
    content: "A hands-on exercise to test your understanding. Try it before reading the solution.";
}
.callout.key-takeaway .callout-title::after {
    content: "The essential takeaway from this section that you should remember.";
}
.callout p:last-child { margin-bottom: 0; }

/* Callout icons via CSS (single source of truth) */
/* Uses emoji icons - universal, no external dependencies */
.callout .callout-title::before {
    display: inline-block;
    width: 1.2em;
    height: 1.2em;
    margin-right: 0.4em;
    vertical-align: middle;
    font-size: 1.1em;
    line-height: 1;
}
.callout.big-picture .callout-title::before { content: '\1F441\200D\1F5E8'; } /* eye */
.callout.key-insight .callout-title::before { content: '\1F4A1'; } /* bulb */
.callout.note .callout-title::before { content: '\1F4DD'; } /* memo */
.callout.warning .callout-title::before { content: '\26A0'; } /* warning */
.callout.practical-example .callout-title::before { content: '\1F527'; } /* wrench */
.callout.fun-note .callout-title::before { content: '\2728'; } /* sparkles */
.callout.research-frontier .callout-title::before { content: '\1F52C'; } /* telescope */
.callout.algorithm .callout-title::before { content: '\1F4CA'; } /* chart */
.callout.tip .callout-title::before { content: '\2705'; } /* checkmark */
.callout.exercise .callout-title::before { content: '\270F'; } /* pencil */
.callout.key-takeaway .callout-title::before { content: '\1F3AF'; } /* target */
.callout.real-world-scenario .callout-title::before { content: '\1F3E2'; } /* office */

/* 1. Big Picture (purple) */
.callout.big-picture {
    background: linear-gradient(135deg, #f3e5f5, #ede7f6);
    border-color: #ce93d8;
    border-left-color: #8e24aa;
}
.callout.big-picture .callout-title { color: #6a1b9a; }

/* 2. Key Insight (green) */
.callout.key-insight {
    background: linear-gradient(135deg, #e8f5e9, #f1f8e9);
    border-color: #a5d6a7;
    border-left-color: #43a047;
}
.callout.key-insight .callout-title { color: #2e7d32; }

/* 3. Note (blue) */
.callout.note {
    background: linear-gradient(135deg, #e3f2fd, #e8eaf6);
    border-color: #90caf9;
    border-left-color: #1976d2;
}
.callout.note .callout-title { color: #1565c0; }

/* 4. Warning (amber) */
.callout.warning {
    background: linear-gradient(135deg, #fff8e1, #fff3e0);
    border-color: #ffcc80;
    border-left-color: #f57c00;
}
.callout.warning .callout-title { color: #e65100; }

/* 5. Practical Example (teal) */
.callout.practical-example {
    background: linear-gradient(135deg, #e0f2f1, #e8f5e9);
    border-color: #80cbc4;
    border-left-color: #00897b;
}
.callout.practical-example .callout-title { color: #00695c; }
.callout.practical-example pre {
    background: #e0f2f1;
    color: #1a3c3a;
    border: 1px solid #80cbc4;
    border-radius: 6px;
    font-size: 0.85rem;
    line-height: 1.6;
}

/* 6. Fun Note (pink) */
.callout.fun-note {
    background: linear-gradient(135deg, #fce4ec, #f3e5f5);
    border-color: #f48fb1;
    border-left-color: #e91e63;
}
.callout.fun-note .callout-title { color: #c2185b; }

/* 7. Research Frontier (teal/cyan) */
.callout.research-frontier {
    background: linear-gradient(135deg, #e0f2f1, #e0f7fa);
    border-color: #80cbc4;
    border-left-color: #00897b;
}
.callout.research-frontier .callout-title { color: #00796b; }

/* 8. Algorithm (indigo) */
.callout.algorithm {
    background: linear-gradient(135deg, #f3effc, #eceaf8);
    border-color: #9581c4;
    border-left-color: #4a55a2;
}
.callout.algorithm .callout-title { color: #2e3990; }
.callout.algorithm pre {
    background: #faf8ff;
    color: #1a1a2e;
    border: 1px solid #c5b8e0;
    font-size: 0.88rem;
    line-height: 1.7;
}

/* 9. Tip (cyan) */
.callout.tip {
    background: linear-gradient(135deg, #e0f7fa, #e1f5fe);
    border-color: #80deea;
    border-left-color: #00acc1;
}
.callout.tip .callout-title { color: #00838f; }

/* 10. Exercise (deep orange) */
.callout.exercise {
    background: linear-gradient(135deg, #fbe9e7, #fff3e0);
    border-color: #ffab91;
    border-left-color: #e64a19;
}
.callout.exercise .callout-title { color: #bf360c; }
.callout.exercise details { margin-top: 1rem; }
.callout.exercise details summary {
    cursor: pointer;
    font-weight: 600;
    color: #bf360c;
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 0.9rem;
}

/* 11. Key Takeaway (teal, reuses key-insight icon) */
.callout.key-takeaway {
    background: linear-gradient(135deg, #e0f2f1, #e0f7fa);
    border-color: #80cbc4;
    border-left-color: #00897b;
}
.callout.key-takeaway .callout-title { color: #00695c; }

/* Legacy aliases - map to canonical types */
.callout.info { background: linear-gradient(135deg, #e3f2fd, #e8eaf6); border-color: #90caf9; border-left-color: #1976d2; }
.callout.info .callout-title { color: #1565c0; }
.callout.info .callout-title::before { content: '\1F4DD'; } /* memo emoji */
.callout.info .callout-title::after { content: "Additional detail or clarification that supplements the main text."; }

.callout.best-practice { background: linear-gradient(135deg, #e8f5e9, #f1f8e9); border-color: #81c784; border-left-color: #388e3c; }
.callout.best-practice .callout-title { color: #1b5e20; }
.callout.best-practice .callout-title::before { content: '\1F3AF'; } /* target emoji */
.callout.best-practice .callout-title::after { content: "A best practice recommended by experienced practitioners."; }

.callout.aha-moment { background: linear-gradient(135deg, #fff8e1, #fffde7); border-color: #ffd54f; border-left-color: #ff8f00; }
.callout.aha-moment .callout-title { color: #e65100; font-weight: 700; }
.callout.aha-moment .callout-title::before { content: '\1F911'; } /* brain emoji */
.callout.aha-moment .callout-title::after { content: "A memorable insight that changes how you think about the topic."; }

.callout.signature-phrase { background: linear-gradient(135deg, #f3e5f5, #ede7f6); border-color: #ce93d8; border-left-color: #8e24aa; }
.callout.signature-phrase .callout-title { color: #6a1b9a; font-weight: 700; font-size: 1.05rem; }
.callout.signature-phrase .callout-title::before { content: '\1F4DD'; } /* memo emoji */
.callout.signature-phrase .callout-title::after { content: "A memorable phrase or rule that captures the key idea."; }
.callout.signature-phrase p { margin-bottom: 0.5rem; }

/* 12. Real World Scenario (navy blue / professional) */
.callout.real-world-scenario {
    background: linear-gradient(135deg, #e8eaf6, #e3f2fd);
    border-color: #9fa8da;
    border-left-color: #3949ab;
}
.callout.real-world-scenario .callout-title { 
    color: #283593; 
}
.callout.real-world-scenario .callout-title::before { 
    content: '\1F3E2'; /* office emoji */
}
.callout.real-world-scenario .callout-title::after { 
    content: "A real-world case study showing how practitioners applied this concept in production systems."; 
}

/* Legacy non-canonical callout classes used in book content */
.case-study {
    background: linear-gradient(135deg, #e0f2f1, #e8f5e9);
    border: 1px solid #80cbc4;
    border-left: 5px solid #00897b;
    border-radius: 0 8px 8px 0;
    padding: 1.2rem 1.5rem;
    margin: 1.5rem 0;
}
.case-study h4 {
    color: #00695c;
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 1rem;
    font-weight: 700;
    margin: 0 0 0.5rem;
}
.case-study p {
    color: #333;
    line-height: 1.6;
    margin-bottom: 0.5rem;
}

.skill-demonstration {
    background: linear-gradient(135deg, #e0f7fa, #e1f5fe);
    border: 1px solid #80deea;
    border-left: 5px solid #00acc1;
    border-radius: 0 8px 8px 0;
    padding: 1.2rem 1.5rem;
    margin: 1.5rem 0;
}
.skill-demonstration h4 {
    color: #00838f;
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 1rem;
    font-weight: 700;
    margin: 0 0 0.5rem;
}
.skill-demonstration p,
.skill-demonstration ul,
.skill-demonstration ol {
    color: #333;
    line-height: 1.6;
    margin-bottom: 0.5rem;
}
.skill-demonstration ul,
.skill-demonstration ol {
    padding-left: 1.5rem;
}
.skill-demonstration li {
    margin-bottom: 0.25rem;
}

/* Emoji fallback for icons (when PNGs not available) */
.callout .callout-title:empty::before,
.callout .callout-title:not(:has(+ img))::before {
    content: '';
}

.callout-title {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-weight: 700;
    font-size: 0.95rem;
    letter-spacing: 0.3px;
    margin-bottom: 0.5rem;
}
.callout p:last-child { margin-bottom: 0; }

/* Big Picture (purple) */
.callout.big-picture {
    background: linear-gradient(135deg, #f3e5f5, #ede7f6);
    border-color: #ce93d8;
    border-left-color: #8e24aa;
}
.callout.big-picture .callout-title { color: #6a1b9a; }

/* Key Insight (green) */
.callout.key-insight {
    background: linear-gradient(135deg, #e8f5e9, #f1f8e9);
    border-color: #a5d6a7;
    border-left-color: #43a047;
}
.callout.key-insight .callout-title { color: #2e7d32; }

/* Note (blue) */
.callout.note {
    background: linear-gradient(135deg, #e3f2fd, #e8eaf6);
    border-color: #90caf9;
    border-left-color: #1976d2;
}
.callout.note .callout-title { color: #1565c0; }

/* Warning (amber) */
.callout.warning {
    background: linear-gradient(135deg, #fff8e1, #fff3e0);
    border-color: #ffcc80;
    border-left-color: #f57c00;
}
.callout.warning .callout-title { color: #e65100; }

/* Info (same as note) */
.callout.info {
    background: linear-gradient(135deg, #e3f2fd, #e8eaf6);
    border-color: #90caf9;
    border-left-color: #1976d2;
}
.callout.info .callout-title { color: #1565c0; }

/* Fun Note (pink) */
.callout.fun-note {
    background: linear-gradient(135deg, #fce4ec, #f3e5f5);
    border-color: #f48fb1;
    border-left-color: #e91e63;
}
.callout.fun-note .callout-title { color: #c2185b; }

/* Research Frontier (teal/cyan) */
.callout.research-frontier {
    background: linear-gradient(135deg, #e0f2f1, #e0f7fa);
    border-color: #80cbc4;
    border-left-color: #00897b;
}
.callout.research-frontier .callout-title { color: #00796b; }

/* Tip (cyan) */
.callout.tip {
    background: linear-gradient(135deg, #e0f7fa, #e1f5fe);
    border-color: #80deea;
    border-left-color: #00acc1;
}
.callout.tip .callout-title { color: #00838f; }

/* Exercise (deep orange) */
.callout.exercise {
    background: linear-gradient(135deg, #fbe9e7, #fff3e0);
    border-color: #ffab91;
    border-left-color: #e64a19;
}
.callout.exercise .callout-title { color: #bf360c; }

/* Algorithm (indigo) */
.callout.algorithm {
    background: linear-gradient(135deg, #f3effc, #eceaf8);
    border-color: #9581c4;
    border-left-color: #4a55a2;
}
.callout.algorithm .callout-title { color: #2e3990; }

/* Best Practice (green/leaf) */
.callout.best-practice {
    background: linear-gradient(135deg, #e8f5e9, #f1f8e9);
    border-color: #81c784;
    border-left-color: #388e3c;
}
.callout.best-practice .callout-title { color: #1b5e20; }
.callout.best-practice::before {
    content: "\1F4C8";
    font-size: 1.2rem;
    margin-right: 0.5rem;
}

/* Aha Moment (gold/star) */
.callout.aha-moment {
    background: linear-gradient(135deg, #fff8e1, #fffde7);
    border-color: #ffd54f;
    border-left-color: #ff8f00;
}
.callout.aha-moment .callout-title { color: #e65100; font-weight: 700; }
.callout.aha-moment::before {
    content: "\1F4A1";
    font-size: 1.2rem;
    margin-right: 0.5rem;
}

/* Signature Phrase / Mnemonic (purple/lightbulb) */
.callout.signature-phrase {
    background: linear-gradient(135deg, #f3e5f5, #ede7f6);
    border: 1px solid #ce93d8;
    border-left: 4px solid #8e24aa;
    border-radius: 0 8px 8px 0;
    padding: 1rem 1.2rem;
    margin: 1.5rem 0;
}
.callout.signature-phrase .callout-title {
    color: #6a1b9a;
    font-weight: 700;
    font-size: 1.05rem;
    margin-bottom: 0.5rem;
}
.callout.signature-phrase p {
    margin: 0;
    line-height: 1.6;
}

/* ----- Prerequisites ----- */
.prereqs,
.prerequisites {
    margin: 1.5rem 0 2rem;
    padding: 1.2rem 1.5rem;
    background: linear-gradient(135deg, rgba(15,52,96,0.04), rgba(233,69,96,0.02));
    border: 1px solid rgba(15,52,96,0.12);
    border-left: 5px solid var(--accent);
    border-radius: 0 8px 8px 0;
    font-size: 0.95rem;
    line-height: 1.6;
}
.prereqs h3,
.prerequisites h3 {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 1.1rem;
    font-weight: 700;
    color: var(--accent);
    margin: 0 0 0.5rem;
}
.prereqs a,
.prerequisites a {
    color: var(--highlight);
    text-decoration: none;
    border-bottom: 1px dotted var(--highlight);
}
.prereqs a:hover,
.prerequisites a:hover { border-bottom-style: solid; }

/* ----- Chapter Overview ----- */
.overview {
    max-width: 750px;
    margin: 2rem auto 2.5rem;
    padding: 1.6rem 2rem;
    background: linear-gradient(135deg, rgba(15,52,96,0.05), rgba(15,52,96,0.02));
    border: 1px solid rgba(15,52,96,0.12);
    border-left: 4px solid var(--accent);
    border-radius: 0 10px 10px 0;
    font-size: 0.97rem;
    line-height: 1.75;
}
.overview h2 {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 1.25rem;
    color: var(--accent);
    margin: 0 0 0.8rem;
    padding-bottom: 0.4rem;
    border-bottom: 2px solid rgba(15,52,96,0.15);
}
.overview p { text-align: left; }
.overview p:last-child { margin-bottom: 0; }

/* ----- Chapter Objective ----- */
.chapter-objective {
    background: linear-gradient(135deg, #e3f2fd, #e8eaf6);
    border-left: 4px solid #1976d2;
    padding: 1rem 1.2rem;
    border-radius: 0 8px 8px 0;
    margin-bottom: 1.5rem;
    font-size: 0.95rem;
    line-height: 1.6;
}
.chapter-objective strong {
    color: #1565c0;
}

/* ----- Opening Hook ----- */
.opening-hook {
    font-size: 1.1rem;
    line-height: 1.7;
    color: #1a1a1a;
    margin-bottom: 1.2rem;
    padding: 1.2rem 1.5rem;
    background: linear-gradient(135deg, #fff9c4, #fffde7);
    border-left: 4px solid #f9a825;
    border-radius: 0 8px 8px 0;
    position: relative;
}
.opening-hook::before {
    content: "\1F4A1"; /* Light bulb emoji */
    position: absolute;
    left: -8px;
    top: -8px;
    font-size: 1.2rem;
    background: #fff9c4;
    padding: 2px 4px;
    border-radius: 50%;
}
.opening-hook strong {
    color: #e65100;
    font-weight: 700;
}

/* ----- Four Questions This Chapter Answers ----- */
.four-questions {
    background: linear-gradient(135deg, #e8f5e9, #f1f8e9);
    border: 1px solid #a5d6a7;
    border-left: 5px solid #43a047;
    border-radius: 0 8px 8px 0;
    padding: 1.2rem 1.5rem;
    margin: 1.5rem 0;
    position: relative;
}
.four-questions::before {
    content: "\1F4DD"; /* Memo emoji */
    position: absolute;
    right: 12px;
    top: -8px;
    font-size: 1.2rem;
    background: #e8f5e9;
    padding: 2px 4px;
    border-radius: 50%;
}
.four-questions h2 {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-weight: 700;
    font-size: 1rem;
    letter-spacing: 0.5px;
    color: #2e7d32;
    margin-top: 0;
    margin-bottom: 1rem;
    padding-bottom: 0.5rem;
    border-bottom: 1px solid #a5d6a7;
    text-transform: uppercase;
}
.four-questions ol {
    margin: 0;
    padding-left: 1.5rem;
}
.four-questions li {
    margin-bottom: 0.75rem;
    line-height: 1.5;
}
.four-questions li strong {
    color: #1b5e20;
}

/* ----- Quiz / Check Your Understanding ----- */
.quiz,
.quiz-box {
    background: linear-gradient(135deg, #e8eaf6, #e3f2fd);
    border: 1px solid #7986cb;
    border-left: 5px solid #3949ab;
    border-radius: 0 8px 8px 0;
    padding: 1.2rem 1.5rem;
    margin: 1.5rem 0;
}
.quiz h3, .quiz-box h3 {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-weight: 700;
    font-size: 0.95rem;
    letter-spacing: 0.3px;
    color: #283593;
    margin-top: 0;
    margin-bottom: 0.5rem;
}
.quiz-question { margin: 1.2rem 0 0.5rem; font-weight: 600; }
details { margin: 0.5rem 0 1.2rem; }
summary {
    cursor: pointer;
    color: var(--accent);
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 0.9rem;
    font-weight: 600;
    padding: 0.3rem 0;
}
summary:hover { text-decoration: underline; }
details .answer {
    padding: 0.8rem 1rem;
    background: #eef;
    border-radius: 6px;
    margin-top: 0.5rem;
}

/* ----- Key Takeaways ----- */
.takeaways {
    background: linear-gradient(135deg, #e0f2f1, #e0f7fa);
    border: 1px solid #80cbc4;
    border-left: 5px solid #00897b;
    border-radius: 0 8px 8px 0;
    padding: 1.2rem 1.5rem;
    margin: 1.5rem 0;
}
.takeaways h2,
.takeaways h3 {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-weight: 700;
    font-size: 0.95rem;
    letter-spacing: 0.3px;
    border-bottom: none;
    margin-top: 0;
    margin-bottom: 0.5rem;
    color: #00695c;
}
.takeaways ul { margin-top: 0.5rem; }
.takeaways li:last-child { margin-bottom: 0; }

/* ----- Chapter Opener Illustration ----- */
.chapter-opener {
    margin: 2rem auto;
    text-align: center;
}
.chapter-opener img {
    max-width: 100%;
    border-radius: 8px;
    box-shadow: 0 4px 12px rgba(0,0,0,0.1);
}
.chapter-opener figcaption {
    text-align: center;
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 0.88rem;
    color: #555;
    margin-top: 0.75rem;
    line-height: 1.5;
    font-style: italic;
}
.chapter-opener figcaption strong {
    font-style: normal;
    color: var(--accent);
    font-weight: 700;
}

/* ----- Figure and Figcaption (LLMBook-style) ----- */
figure {
    margin: 2rem 0;
}
figure img {
    max-width: 100%;
    border-radius: 8px;
    display: block;
    margin: 0 auto;
}
figcaption {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 0.9rem;
    font-weight: 600;
    color: #444;
    text-align: center;
    margin-top: 0.75rem;
    line-height: 1.5;
}
figcaption strong {
    color: var(--accent);
    font-weight: 700;
}
/* Figure number format: "Figure X.Y.Z: description" */
figcaption::before {
    content: '';
}
/* LLMBook-style: Figure number bold, description follows */

/* ----- Table Caption ----- */
table {
    caption-side: bottom;
}
table + p.caption,
.caption {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 0.85rem;
    font-weight: 600;
    color: #444;
    text-align: center;
    margin-top: 0.5rem;
    line-height: 1.4;
}
table + p.caption::before,
.caption::before {
    content: 'Table: ';
    font-weight: 700;
    color: var(--accent);
}

/* ----- Example Box (non-canonical but widely used) ----- */
.example-box {
    background: linear-gradient(135deg, #f5f5f5, #fafafa);
    border: 1px solid #e0e0e0;
    border-left: 5px solid #5dade2;
    border-radius: 0 8px 8px 0;
    padding: 1.2rem 1.5rem;
    margin: 1.5rem 0;
}
.example-box .example-title {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-weight: 700;
    font-size: 0.95rem;
    color: #2980b9;
    margin-bottom: 0.75rem;
}
.example-box p { margin-bottom: 0.75rem; }
.example-box p:last-child { margin-bottom: 0; }
.example-box pre {
    background: var(--code-bg);
    color: var(--code-text);
    padding: 1rem;
    border-radius: 6px;
    margin: 1rem 0;
    font-size: 0.88rem;
}

/* ----- Code Caption ----- */
.code-caption {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 0.85rem;
    font-weight: 500;
    color: #555;
    text-align: center;
    margin-top: 0.3rem;
    margin-bottom: 1.8rem;
    padding: 0 1rem;
    line-height: 1.5;
    font-style: italic;
}

/* ----- Code blocks ----- */
pre {
    background: var(--code-bg);
    color: var(--code-text);
    padding: 1.5rem;
    border-radius: 8px;
    overflow-x: auto;
    margin: 1.2rem 0;
    font-family: 'Consolas', 'Fira Code', monospace;
    font-size: 0.92rem;
    line-height: 1.6;
}
code {
    font-family: 'Consolas', 'Fira Code', monospace;
    font-size: 0.92em;
}
p code, li code {
    background: #eef;
    padding: 0.15rem 0.4rem;
    border-radius: 3px;
    color: var(--accent);
}
pre code {
    background: none;
    padding: 0;
    border-radius: 0;
    color: inherit;
    font-size: inherit;
}

/* ----- Tables ----- */
table {
    width: 100%;
    border-collapse: collapse;
    margin: 1.5rem 0;
    font-size: 0.95rem;
}
th, td {
    padding: 0.75rem 1rem;
    text-align: left;
    border-bottom: 1px solid #ddd;
}
th {
    background: var(--primary);
    color: white;
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 0.85rem;
    text-transform: uppercase;
    letter-spacing: 1px;
}
tr:nth-child(even) { background: #f8f8f8; }

/* ----- What's Next ----- */
.whats-next {
    background: linear-gradient(135deg, #e3f2fd, #e8eaf6);
    border: 1px solid #90caf9;
    border-left: 4px solid #1565c0;
    border-radius: 10px;
    padding: 1.2rem 1.5rem;
    margin: 1.5rem 0;
}
.whats-next h2,
.whats-next h3 {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-weight: 700;
    font-size: 0.95rem;
    letter-spacing: 0.3px;
    color: #1565c0;
    margin: 0 0 0.5rem;
}
.whats-next p:last-child { margin-bottom: 0; }
.whats-next h2::before { content: "\27A1\00a0"; font-size: 1.1em; }

/* ----- Bibliography ----- */
.bibliography {
    margin-top: 3rem;
    padding: 2rem;
    background: linear-gradient(135deg, rgba(15,52,96,0.04), rgba(233,69,96,0.02));
    border-radius: 8px;
    border: 1px solid rgba(15,52,96,0.1);
}
.bibliography-title {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-weight: 700;
    font-size: 0.95rem;
    letter-spacing: 0.3px;
    color: var(--accent);
    margin-bottom: 1.2rem;
    padding-bottom: 0.5rem;
    border-bottom: 2px solid var(--highlight);
}
.bib-entry-card {
    padding: 0.8rem 1rem;
    margin-bottom: 0.8rem;
    background: white;
    border-radius: 6px;
    border: 1px solid rgba(0,0,0,0.06);
}
.bib-ref {
    font-size: 0.95rem;
    line-height: 1.5;
    margin: 0;
}
.bib-ref a {
    color: var(--accent);
    text-decoration: none;
    font-weight: 600;
}
.bib-ref a:hover { color: var(--highlight); }
.bib-annotation {
    font-size: 0.88rem;
    color: var(--text-light);
    margin: 0.4rem 0 0;
    line-height: 1.5;
}

/* ----- Chapter cards ----- */
.chapter-card {
    background: white;
    border: 1px solid rgba(0,0,0,0.08);
    border-radius: 12px;
    margin-bottom: 1.5rem;
    overflow: hidden;
    transition: box-shadow 0.25s, transform 0.25s;
}
.chapter-card:hover {
    box-shadow: 0 6px 20px rgba(0,0,0,0.09);
    transform: translateY(-3px);
}
.chapter-card-header {
    background: linear-gradient(135deg, var(--primary), var(--accent));
    color: white;
    padding: 1.1rem 1.5rem;
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 1.05rem;
    font-weight: 600;
}
.chapter-card-header a { color: white; text-decoration: none; }
.chapter-card-header a:hover { opacity: 0.9; }
.chapter-card-header .mod-num {
    background: rgba(255,255,255,0.2);
    padding: 2px 10px;
    border-radius: 16px;
    font-size: 0.8rem;
    font-weight: 600;
    margin-right: 0.5rem;
}
.chapter-card-body {
    padding: 1.3rem 1.5rem;
    font-size: 0.93rem;
    line-height: 1.6;
}
.chapter-card-body p { margin-bottom: 0.8rem; }
.chapter-card-body .section-list {
    list-style: none;
    padding: 0;
    margin: 0.6rem 0 0;
    border-top: 1px solid #f0f0f0;
}
.chapter-card-body .section-list li {
    padding: 0.4rem 0;
    border-bottom: 1px solid #f0f0f0;
    font-size: 0.9rem;
}
.chapter-card-body .section-list li:last-child { border-bottom: none; }
.chapter-card-body .section-list a {
    color: var(--accent);
    text-decoration: none;
    display: block;
    padding: 0.1rem 0.4rem;
    border-radius: 4px;
    transition: background 0.15s;
}
.chapter-card-body .section-list a:hover {
    color: var(--highlight);
    background: rgba(15,52,96,0.04);
}
.chapter-card-body .section-list .sec-num {
    color: var(--highlight);
    font-weight: 700;
    margin-right: 0.4rem;
    min-width: 2.2rem;
    display: inline-block;
    font-family: 'Segoe UI', system-ui, sans-serif;
}

/* ----- Section cards ----- */
.sections-list {
    list-style: none;
    padding: 0;
    margin: 0;
    display: flex;
    flex-direction: column;
    gap: 0.6rem;
}
.sections-list li { margin: 0; }
.section-card {
    display: flex;
    flex-wrap: wrap;
    align-items: flex-start;
    gap: 0.8rem;
    padding: 1.2rem 1.4rem;
    background: white;
    border: 1px solid rgba(0,0,0,0.06);
    border-left: 4px solid var(--accent);
    border-radius: 0 8px 8px 0;
    transition: box-shadow 0.2s, transform 0.2s, border-color 0.2s;
    text-decoration: none;
    color: inherit;
}
.section-card:hover {
    box-shadow: 0 4px 16px rgba(0,0,0,0.08);
    transform: translateY(-2px);
    border-left-color: var(--highlight);
}
.section-num {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 0.85rem;
    font-weight: 700;
    color: white;
    background: var(--accent);
    padding: 0.3rem 0.7rem;
    border-radius: 6px;
    min-width: 2.5rem;
    text-align: center;
    flex-shrink: 0;
}
.section-card:hover .section-num { background: var(--highlight); }
.section-title {
    font-weight: 600;
    color: var(--primary);
    font-size: 1rem;
    flex: 1 1 60%;
}
.section-desc {
    font-size: 0.88rem;
    color: var(--text-light);
    line-height: 1.55;
    flex: 1 1 100%;
    margin-top: -0.2rem;
}

/* ----- TOC ----- */
.toc {
    max-width: 820px;
    margin: 0 auto;
    padding: 3rem 2rem;
}
.toc h1 {
    font-size: 2.2rem;
    text-align: center;
    margin-bottom: 2rem;
    color: var(--primary);
}
.toc h2 {
    font-size: 1.4rem;
    margin-top: 2.5rem;
    margin-bottom: 1rem;
    color: var(--accent);
    border-bottom: 2px solid var(--highlight);
    padding-bottom: 0.5rem;
}
.toc h3 {
    font-size: 1.1rem;
    margin-top: 1.5rem;
    margin-bottom: 0.75rem;
    color: var(--primary);
}
.toc .part-intro {
    font-size: 0.95rem;
    color: var(--text-light);
    margin-bottom: 1.5rem;
    font-style: italic;
    line-height: 1.6;
}
.toc ul {
    list-style: none;
    padding: 0;
}
.toc li {
    margin-bottom: 0.5rem;
}
.toc a {
    color: var(--text);
    text-decoration: none;
    display: block;
    padding: 0.4rem 0.6rem;
    border-radius: 4px;
    transition: background 0.2s;
}
.toc a:hover {
    background: var(--bg-secondary);
    text-decoration: none;
}
.toc .chapter-num {
    color: var(--text-light);
    font-size: 0.85rem;
    margin-right: 0.5rem;
}

/* ----- Hero/Home ----- */
.hero {
    text-align: center;
    padding: 4rem 2rem;
    background: linear-gradient(135deg, var(--primary), var(--accent));
    color: white;
}
.hero h1 {
    font-size: 2.8rem;
    font-weight: 700;
    margin-bottom: 1rem;
    line-height: 1.2;
}
.hero .subtitle {
    font-size: 1.3rem;
    opacity: 0.9;
    margin-bottom: 1.5rem;
}
.hero .meta {
    font-size: 0.9rem;
    opacity: 0.7;
}

.book-description {
    max-width: 820px;
    margin: 0 auto;
    padding: 3rem 2rem;
}
.book-description h2 {
    text-align: center;
    margin-bottom: 2rem;
}
.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 1.5rem;
    margin-top: 2rem;
}
.feature-card {
    background: white;
    padding: 1.5rem;
    border-radius: 10px;
    border: 1px solid rgba(0,0,0,0.08);
    transition: box-shadow 0.2s, transform 0.2s;
}
.feature-card:hover {
    box-shadow: 0 4px 16px rgba(0,0,0,0.1);
    transform: translateY(-2px);
}
.feature-card h3 {
    margin-top: 0;
    font-size: 1.1rem;
    color: var(--accent);
}
.feature-card p {
    font-size: 0.95rem;
    color: var(--text-light);
    margin-bottom: 0;
}
.cta {
    text-align: center;
    padding: 2rem;
    margin-top: 2rem;
}
.cta a {
    display: inline-block;
    padding: 1rem 2rem;
    background: var(--accent);
    color: white;
    text-decoration: none;
    border-radius: 8px;
    font-weight: 600;
    transition: background 0.2s;
}
.cta a:hover {
    background: var(--highlight);
    text-decoration: none;
}

/* ----- Loop Diagram ----- */
.loop-diagram {
    text-align: center;
    font-size: 1.1em;
    font-weight: 600;
    margin: 1rem 0;
}

/* ----- Code output ----- */
.code-output {
    background: #f5f5f0;
    border-left: 4px solid #888;
    color: #333;
    padding: 1rem 1.5rem;
    border-radius: 0 8px 8px 0;
    margin: -0.5rem 0 1.5rem;
    font-family: 'Consolas', monospace;
    font-size: 0.88rem;
    line-height: 1.5;
}
.code-output::before {
    content: "Output";
    display: block;
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 0.75rem;
    text-transform: uppercase;
    letter-spacing: 1px;
    color: #888;
    margin-bottom: 0.5rem;
}

/* ----- Comparison Tables ----- */
.comparison-table {
    margin: 1.5rem 0;
    border-radius: 8px;
    overflow: hidden;
    border: 1px solid #d8dce6;
    background: #fff;
}
.comparison-table-title {
    background: linear-gradient(135deg, #1a1a2e 0%, #16213e 100%);
    color: #fff;
    padding: 0.7rem 1.2rem;
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 0.95rem;
    font-weight: 600;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}
.comparison-table-title::before {
    content: '\2696';
    font-size: 1.1rem;
}
.comparison-table table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.9rem;
}
.comparison-table th {
    background: #f0f2f8;
    padding: 0.6rem 0.8rem;
    text-align: left;
    font-weight: 600;
    color: #1a1a2e;
    border-bottom: 2px solid #d8dce6;
    font-size: 0.85rem;
}
.comparison-table td {
    padding: 0.5rem 0.8rem;
    border-bottom: 1px solid #eee;
    vertical-align: top;
    line-height: 1.5;
}
.comparison-table tr:last-child td {
    border-bottom: none;
}
.comparison-table tr:nth-child(even) td {
    background: #f8f9fc;
}
.comparison-table .winner {
    color: #27ae60;
    font-weight: 600;
}
.comparison-table .caution {
    color: #e67e22;
    font-weight: 600;
}

/* ----- Glossary ----- */
.glossary-list { list-style: none; padding: 0; }
.glossary-entry { padding: 0.8rem 0; border-bottom: 1px solid #f0f0f0; }
.glossary-term { font-weight: 700; color: var(--primary); font-size: 1.05rem; }
.glossary-def { margin-top: 0.3rem; font-size: 0.95rem; line-height: 1.6; }
.glossary-xref { font-size: 0.85rem; color: var(--text-light); margin-top: 0.2rem; }
.glossary-xref a { color: var(--accent); }

/* ----- Labs ----- */
.lab {
    background: linear-gradient(135deg, #e8eaf6, #e3f2fd);
    border: 2px solid var(--accent);
    border-radius: 10px;
    padding: 2rem;
    margin: 2.5rem 0;
}
.lab-meta {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 0.85rem;
    color: var(--text-light);
    margin-bottom: 1rem;
}
.lab-step {
    background: white;
    border-radius: 8px;
    padding: 1.2rem;
    margin: 1rem 0;
    border: 1px solid rgba(0,0,0,0.06);
}
.lab-expected {
    background: #f1f8e9;
    border-left: 4px solid #43a047;
    padding: 1rem 1.5rem;
    border-radius: 0 8px 8px 0;
    margin: 1rem 0;
}
.lab-stretch {
    background: #fff8e1;
    border-left: 4px solid #f57c00;
    padding: 1rem 1.5rem;
    border-radius: 0 8px 8px 0;
    margin: 1rem 0;
}
.lab-objective {
    background: linear-gradient(135deg, #e3f2fd, #f3e5f5);
    border-left: 4px solid #1e88e5;
    padding: 1rem 1.2rem;
    border-radius: 0 8px 8px 0;
    margin-bottom: 1.2rem;
    font-size: 0.95rem;
    line-height: 1.6;
}
.lab-skills { margin-bottom: 1.2rem; }
.lab-skills h4 { font-size: 0.9rem; text-transform: uppercase; letter-spacing: 0.5px; color: #555; margin-bottom: 0.5rem; }
.lab-skills ul { padding-left: 1.5rem; }
.lab-skills li { margin-bottom: 0.3rem; font-size: 0.92rem; }
.lab-prereqs {
    background: #fafafa;
    border: 1px solid #e0e0e0;
    border-radius: 8px;
    padding: 1rem 1.2rem;
    margin-bottom: 1.2rem;
    font-size: 0.9rem;
}
.lab-prereqs h4 { font-size: 0.9rem; margin-bottom: 0.5rem; }
.lab-prereqs code { background: #e8e8e8; padding: 0.15em 0.4em; border-radius: 3px; font-size: 0.85rem; }
.lab-solution summary {
    cursor: pointer;
    font-weight: 600;
    color: var(--accent);
    padding: 0.5rem 0;
    font-size: 0.95rem;
}
.lab-solution summary:hover { color: var(--highlight); }

/* ----- Math ----- */
.math {
    white-space: nowrap;
    background: #f4f6fa;
    padding: 0.1em 0.3em;
    border-radius: 3px;
    border: 1px solid #e4e7ef;
    font-size: 0.95em;
    vertical-align: baseline;
    line-height: inherit;
}
.math-block {
    position: relative;
    background: linear-gradient(135deg, #f8f9fc 0%, #f0f2f8 100%);
    border: 1px solid #d8dce6;
    border-left: 4px solid var(--accent);
    border-radius: 6px;
    padding: 1.2rem 1.5rem;
    margin: 1.5rem 0;
    text-align: center;
    font-size: 1.1rem;
    line-height: 1.8;
    overflow-x: auto;
}
.math-block-label {
    display: block;
    text-align: left;
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-style: normal;
    font-size: 0.82rem;
    font-weight: 600;
    color: var(--accent);
    letter-spacing: 0.04em;
    text-transform: uppercase;
    margin-bottom: 0.5rem;
    padding-bottom: 0.35rem;
    border-bottom: 1px solid #e0e3ea;
}
.math-block .math-where {
    display: block;
    text-align: left;
    font-style: normal;
    font-size: 0.92rem;
    color: #555;
    margin-top: 0.6rem;
    padding-top: 0.5rem;
    border-top: 1px dashed #d8dce6;
    line-height: 1.6;
}

/* ----- Part Overview ----- */
.part-overview {
    margin-bottom: 2rem;
    font-size: 1rem;
    line-height: 1.8;
    background: linear-gradient(135deg, #f8f9fc, #f0f2f8);
    border: 1px solid #d8dce6;
    border-radius: 10px;
    padding: 1.5rem 1.8rem;
}
.part-overview h2 {
    color: var(--accent);
    font-size: 1.15rem;
    margin: 0 0 0.8rem;
}

/* ----- Section Break ----- */
.section-break { margin: 2rem 0; border-top: 1px solid #e0e0e0; }

/* ----- Cross-reference links ----- */
.cross-ref {
    color: #1a6fb5;
    text-decoration: none;
    border-bottom: 1.5px dotted rgba(26, 111, 181, 0.5);
}
.cross-ref:hover {
    color: var(--highlight);
    border-bottom: 2px solid var(--highlight);
}

/* ----- SVG responsive ----- */
.svg-responsive {
    max-width: 100%;
    margin: 1.5rem auto;
    display: block;
}

/* ----- Diagram container ----- */
.diagram-container {
    margin: 2rem 0;
    text-align: center;
}
.diagram-container svg {
    max-width: 100%;
    height: auto;
}
.diagram-caption {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 0.88rem;
    color: #555;
    text-align: center;
    margin-top: 0.5rem;
    line-height: 1.5;
    font-style: italic;
}
.diagram-caption strong {
    font-style: normal;
    color: var(--accent);
    font-weight: 700;
}

/* ----- Footer ----- */
footer {
    text-align: center;
    padding: 2rem;
    color: var(--text-light);
    font-size: 0.85rem;
    border-top: 1px solid #e0e0e0;
    margin-top: auto;
}
footer a {
    color: var(--text-light);
    text-decoration: none;
}
footer a:hover { color: var(--accent); }

/* ----- Responsive ----- */
@media (max-width: 768px) {
    .content { padding: 1.5rem 1rem; }
    .chapter-header { padding: 0 1rem 2rem; }
    .chapter-header h1 { font-size: 1.6rem; }
    .header-nav .book-title-link { font-size: 0.72rem; max-width: 55%; }
    body { font-size: 16px; line-height: 1.75; }
    h2 { font-size: 1.5rem; margin-top: 2rem; }
    h3 { font-size: 1.2rem; }
    table { display: block; overflow-x: auto; -webkit-overflow-scrolling: touch; }
    pre { overflow-x: auto; -webkit-overflow-scrolling: touch; font-size: 0.82rem; }
    .callout { margin-left: 0; margin-right: 0; padding: 1rem 1.2rem; }
    .chapter-nav, nav.chapter-nav { grid-template-columns: 1fr; gap: 0.5rem; }
    .chapter-nav a.next, .chapter-nav a:last-child:not(.up):not(.prev) { justify-content: center; text-align: center; }
    .chapter-nav a.prev, .chapter-nav a:first-child:not(.up):not(.next) { justify-content: center; text-align: center; }
    .chapter-nav a.up, .chapter-nav a:nth-child(2) { order: -1; }
    .features-grid { grid-template-columns: 1fr; }
}

@media (max-width: 480px) {
    .content { padding: 1rem 0.75rem; }
    .chapter-header { padding: 0 0.75rem 1.5rem; }
    .chapter-header h1 { font-size: 1.4rem; }
    .hero h1 { font-size: 2rem; }
    .hero .subtitle { font-size: 1.1rem; }
    h2 { font-size: 1.3rem; }
    h3 { font-size: 1.1rem; }
    pre { font-size: 0.78rem; padding: 0.8rem; }
}

/* ----- Print ----- */
@media print {
    .chapter-header { background: none; color: var(--primary); border-bottom: 2px solid var(--primary); padding-top: 1rem; }
    .header-nav { display: none; }
    .chapter-nav, nav.chapter-nav { display: none; }
    .callout { break-inside: avoid; }
    pre { white-space: pre-wrap; word-wrap: break-word; }
    .whats-next { display: none; }
}

/* ============================================================
   LLMBook-style ToC Classes
   ============================================================ */

/* ToC Toggle Switch */
.toc-toggle {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    margin: 1.5rem 0 1rem 0;
}
.toc-toggle label {
    position: relative;
    display: inline-block;
    width: 44px;
    height: 24px;
    cursor: pointer;
}
.toc-toggle input {
    opacity: 0;
    width: 0;
    height: 0;
}
.toc-toggle .toc-switch-bg {
    position: absolute;
    inset: 0;
    background: #ccc;
    border-radius: 24px;
    transition: background 0.3s ease;
}
.toc-toggle .toc-switch-dot {
    position: absolute;
    top: 2px;
    left: 2px;
    width: 20px;
    height: 20px;
    background: white;
    border-radius: 50%;
    transition: transform 0.3s ease;
    box-shadow: 0 1px 3px rgba(0,0,0,0.2);
}
.toc-toggle input:checked + .toc-switch-bg {
    background: var(--accent);
}
.toc-toggle input:checked + .toc-switch-bg .toc-switch-dot {
    transform: translateX(20px);
}
.toc-toggle span {
    font-size: 0.82rem;
    font-weight: 600;
    cursor: pointer;
    transition: color 0.2s;
}
.toc-toggle #toc-label-short { color: var(--accent); }
.toc-toggle #toc-label-detailed { color: #999; }

/* ToC Parts */
.stoc-part {
    margin-bottom: 0.4rem;
}

.stoc-group {
    padding-left: 0.2rem;
}

/* Part Headers - with links */
.dense-part-header > a {
    font-family: 'Cinzel', Georgia, serif;
    font-size: 0.75rem;
    font-weight: 600;
    color: #444;
    margin: 0.8rem 0 0.3rem;
    padding: 0.2rem 0;
    border-bottom: 1px solid #ddd;
    letter-spacing: 0.12em;
    text-transform: uppercase;
    text-decoration: none;
    display: block;
}
.dense-part-header > a:hover {
    color: #222;
}

/* Part Headers - Front Matter (no link) */
.dense-part-header:not(:has(a)) {
    font-family: 'Cinzel', Georgia, serif;
    font-size: 0.75rem;
    font-weight: 600;
    color: #444;
    margin: 0.8rem 0 0.3rem;
    padding: 0.2rem 0;
    border-bottom: 1px solid #ddd;
    letter-spacing: 0.12em;
    text-transform: uppercase;
}
.dense-part-header a {
    color: inherit;
    text-decoration: none;
}
.dense-part-header a:hover {
    color: #222;
}

.dense-appendices-header {
    font-family: 'Cinzel', Georgia, serif;
    font-size: 0.75rem;
    font-weight: 600;
    color: #444;
    margin: 1.2rem 0 0.3rem;
    padding: 0.2rem 0;
    border-bottom: 1px solid #ccc;
    letter-spacing: 0.12em;
    text-transform: uppercase;
}

/* Chapter Entries */
.dense-chapter {
    display: flex;
    align-items: baseline;
    gap: 0.4rem;
    padding: 0.25rem 0.4rem;
    margin-bottom: 0.1rem;
    border-radius: 4px;
    transition: background 0.2s ease;
}
.dense-chapter:hover {
    background: rgba(15, 52, 96, 0.04);
}
.dense-chapter a {
    color: #333;
    text-decoration: none;
    font-size: 0.75rem;
    line-height: 1.3;
}
.dense-chapter a:hover {
    color: #000;
}

.dense-ch-num {
    font-family: 'Segoe UI', system-ui, sans-serif;
    font-size: 0.7rem;
    font-weight: 600;
    color: #666;
    min-width: 1.8rem;
    flex-shrink: 0;
}

/* Sections (Detailed ToC) */
.dense-sections {
    padding: 0.15rem 0.3rem 0.3rem 2.2rem;
    font-size: 0.75rem;
    color: #777;
    line-height: 1.45;
}
.dense-sections a {
    color: #555;
    text-decoration: none;
    transition: color 0.2s;
}
.dense-sections a:hover {
    color: #333;
    text-decoration: underline;
}