/* ============================================================
   Chapter layout & components — Statistics & DS Visual Handbook
   Reusable across all chapter pages. Pairs with book.css.
   All diagrams on chapter pages are inline SVG / CSS — fully editable.
   ============================================================ */

body.chapter { padding-top: 60px; background: #fbfcfe; color: #1a2138; }

/* Light-theme overrides for chapter reading pages
   (the title/TOC pages are dark; chapters read better light) */
body.chapter {
  --ink:        #1a2138;
  --ink-soft:   #4a5578;
  --ink-faint:  #8b94b3;
  --line:       #e6e9f2;
  --panel:      #ffffff;
  --panel-2:    #f4f6fb;
  --c-cyan:     #0891b2;
  --c-cyan-bg:  #e0f7fb;
  --c-purple:   #7c3aed;
  --c-purple-bg:#f0e9fe;
  --c-amber:    #d97706;
  --c-amber-bg: #fef3e2;
  --c-green:    #059669;
  --c-green-bg: #e3f6ee;
  --c-pink:     #db2777;
  --c-pink-bg:  #fce7f3;
  --c-blue:     #2563eb;
  --c-blue-bg:  #e6effe;
  --c-red:      #dc2626;
}

/* progress bar under nav */
.read-progress {
  position: fixed; top: 60px; left: 0; height: 3px; width: 0%;
  background: linear-gradient(90deg, var(--c-cyan), var(--c-purple), var(--c-amber));
  z-index: 999; transition: width 0.1s linear;
}

/* ---------- Chapter hero ---------- */
.chapter-hero {
  position: relative; overflow: hidden;
  background: linear-gradient(135deg, #0a1230 0%, #141d44 55%, #1b1448 100%);
  color: #fff; padding: 3.5rem 2rem 3rem;
}
.chapter-hero::before {
  content: ""; position: absolute; inset: 0;
  background:
    radial-gradient(600px 300px at 10% -10%, rgba(0,212,255,0.18), transparent 60%),
    radial-gradient(500px 300px at 95% 120%, rgba(124,58,237,0.22), transparent 60%);
  pointer-events: none;
}
.chapter-hero-inner { position: relative; max-width: 880px; margin: 0 auto; }
.crumb {
  display: flex; align-items: center; gap: 10px; flex-wrap: wrap;
  font-size: 0.78rem; color: rgba(255,255,255,0.55); margin-bottom: 1.4rem;
}
.crumb a { color: rgba(255,255,255,0.75); }
.crumb a:hover { color: #fff; }
.crumb .sep { opacity: 0.4; }
.chapter-kicker {
  display: inline-flex; align-items: center; gap: 10px;
  font-size: 0.72rem; font-weight: 700; letter-spacing: 0.14em;
  text-transform: uppercase; color: #00d4ff; margin-bottom: 1rem;
}
.chapter-kicker .pill {
  background: rgba(0,212,255,0.12); border: 1px solid rgba(0,212,255,0.3);
  padding: 3px 10px; border-radius: 100px;
}
.chapter-hero h1 {
  font-size: clamp(2.2rem, 5vw, 3.4rem); font-weight: 900;
  line-height: 1.06; letter-spacing: -0.03em; margin-bottom: 1rem;
}
.chapter-hero h1 .accent {
  background: linear-gradient(110deg, #00d4ff, #a78bfa 60%, #fbbf24);
  -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text;
}
.chapter-hero .dek {
  font-size: 1.05rem; color: rgba(255,255,255,0.75);
  max-width: 640px; line-height: 1.6;
}
.hero-meta {
  display: flex; gap: 1.5rem; flex-wrap: wrap; margin-top: 1.8rem;
  padding-top: 1.5rem; border-top: 1px solid rgba(255,255,255,0.12);
}
.hero-meta .m { display: flex; align-items: center; gap: 8px; font-size: 0.82rem; color: rgba(255,255,255,0.7); }
.hero-meta .m b { color: #fff; font-weight: 700; }

/* ---------- Reading column ---------- */
.reading { max-width: 880px; margin: 0 auto; padding: 3rem 2rem 4rem; }
.reading > section { margin-bottom: 3.2rem; scroll-margin-top: 80px; }

.section-eyebrow {
  display: flex; align-items: center; gap: 12px; margin-bottom: 1.1rem;
}
.section-eyebrow .num {
  width: 34px; height: 34px; border-radius: 9px; flex-shrink: 0;
  display: flex; align-items: center; justify-content: center;
  font-weight: 800; font-size: 0.95rem; color: #fff;
  background: linear-gradient(135deg, var(--c-cyan), var(--c-purple));
}
.section-eyebrow h2 {
  font-size: 1.5rem; font-weight: 800; color: var(--ink); letter-spacing: -0.02em;
}
.reading p { font-size: 1.02rem; line-height: 1.75; color: var(--ink-soft); margin-bottom: 1rem; }
.reading p .hl { color: var(--ink); font-weight: 600; }
.reading p .term { color: var(--c-purple); font-weight: 600; }
.lead { font-size: 1.2rem !important; line-height: 1.7 !important; color: var(--ink) !important; }

/* ---------- Definition card ---------- */
.def-card {
  display: flex; gap: 1.4rem; align-items: flex-start;
  background: var(--panel); border: 1px solid var(--line);
  border-left: 4px solid var(--c-cyan);
  border-radius: 14px; padding: 1.6rem 1.8rem;
  box-shadow: 0 8px 30px rgba(20,30,80,0.05); margin: 1.5rem 0;
}
.def-card .sigma {
  width: 60px; height: 60px; border-radius: 14px; flex-shrink: 0;
  display: flex; align-items: center; justify-content: center;
  font-size: 2rem; font-weight: 800; color: #fff;
  background: linear-gradient(135deg, #0a1230, #2a1a6e);
}
.def-card .def-body strong { color: var(--ink); }
.def-card .def-body { font-size: 1.1rem; line-height: 1.65; color: var(--ink-soft); }
.def-card .def-kw { color: var(--c-purple); font-weight: 700; }

/* ---------- Study brief (capstone openings) ---------- */
.brief-card {
  background: var(--panel); border: 1px solid var(--line);
  border-left: 4px solid var(--c-amber);
  border-radius: 14px; padding: 1.4rem 1.7rem;
  box-shadow: 0 8px 30px rgba(20,30,80,0.05); margin: 1.5rem 0;
}
.brief-card .bh {
  font-size: 0.72rem; font-weight: 800; text-transform: uppercase; letter-spacing: 0.09em;
  color: var(--c-amber); margin-bottom: 0.95rem;
}
.brief-card dl { display: grid; grid-template-columns: 9rem 1fr; gap: 0.6rem 1.2rem; margin: 0; }
.brief-card dt {
  font-size: 0.72rem; font-weight: 800; text-transform: uppercase; letter-spacing: 0.05em;
  color: var(--ink-faint); padding-top: 0.22rem;
}
.brief-card dd { margin: 0; font-size: 0.95rem; line-height: 1.62; color: var(--ink-soft); }
.brief-card dd strong { color: var(--ink); font-weight: 700; }
@media (max-width: 640px) {
  .brief-card { padding: 1.2rem 1.3rem; }
  .brief-card dl { grid-template-columns: 1fr; gap: 0.2rem; }
  .brief-card dd { margin-bottom: 0.7rem; }
  .brief-card dd:last-child { margin-bottom: 0; }
}

/* ---------- Quote ---------- */
.quote {
  position: relative; margin: 2rem 0; padding: 1.5rem 1.8rem 1.5rem 3.4rem;
  background: linear-gradient(135deg, var(--c-purple-bg), var(--c-cyan-bg));
  border-radius: 14px; color: var(--ink);
}
.quote::before {
  content: "\201C"; position: absolute; left: 1rem; top: 0.4rem;
  font-family: Georgia, serif; font-size: 3.5rem; color: var(--c-purple); opacity: 0.45;
}
.quote .q { font-size: 1.15rem; font-style: italic; line-height: 1.5; font-weight: 500; }
.quote .a { display: block; margin-top: 0.6rem; font-size: 0.85rem; font-weight: 700; color: var(--c-purple); font-style: normal; }

/* ---------- Pillars flow (Collect→…→Present) ---------- */
.pillars {
  display: grid; grid-template-columns: repeat(5, 1fr); gap: 0.5rem;
  margin: 1.5rem 0;
}
.pillar {
  position: relative; text-align: center; padding: 1.2rem 0.6rem;
  background: var(--panel); border: 1px solid var(--line); border-radius: 14px;
  transition: all 0.25s ease;
}
.pillar:hover { transform: translateY(-4px); box-shadow: 0 12px 30px rgba(20,30,80,0.10); border-color: transparent; }
.pillar .pic {
  width: 54px; height: 54px; margin: 0 auto 0.7rem; border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
}
.pillar .pname { font-weight: 700; font-size: 0.9rem; color: var(--ink); margin-bottom: 0.3rem; }
.pillar .pdesc { font-size: 0.74rem; color: var(--ink-faint); line-height: 1.4; }
.pillar .pstep {
  position: absolute; top: -10px; left: 50%; transform: translateX(-50%);
  width: 22px; height: 22px; border-radius: 50%; background: var(--ink);
  color: #fff; font-size: 0.7rem; font-weight: 700;
  display: flex; align-items: center; justify-content: center;
}
.pillars .arrow {
  display: flex; align-items: center; justify-content: center; color: var(--ink-faint);
}
@media (max-width: 720px){ .pillars { grid-template-columns: repeat(2, 1fr); } .pillars .arrow{ display:none; } }

/* ---------- Generic feature/info grids ---------- */
.cardgrid { display: grid; gap: 1rem; margin: 1.4rem 0; }
.cols-2 { grid-template-columns: repeat(2, 1fr); }
.cols-3 { grid-template-columns: repeat(3, 1fr); }
.cols-4 { grid-template-columns: repeat(4, 1fr); }
@media (max-width: 720px){ .cols-2,.cols-3,.cols-4 { grid-template-columns: 1fr 1fr; } }
@media (max-width: 480px){ .cols-2,.cols-3,.cols-4 { grid-template-columns: 1fr; } }

.ic-card {
  background: var(--panel); border: 1px solid var(--line); border-radius: 14px;
  padding: 1.3rem; transition: all 0.25s ease;
}
.ic-card:hover { transform: translateY(-3px); box-shadow: 0 12px 28px rgba(20,30,80,0.08); }
.ic-card .ic {
  width: 44px; height: 44px; border-radius: 11px; margin-bottom: 0.85rem;
  display: flex; align-items: center; justify-content: center; font-size: 1.3rem;
}
.ic-card h4 { font-size: 0.98rem; font-weight: 700; color: var(--ink); margin-bottom: 0.35rem; }
.ic-card p { font-size: 0.85rem !important; line-height: 1.55 !important; color: var(--ink-soft) !important; margin: 0 !important; }

/* color helpers */
.bg-cyan{background:var(--c-cyan-bg)} .bg-purple{background:var(--c-purple-bg)}
.bg-amber{background:var(--c-amber-bg)} .bg-green{background:var(--c-green-bg)}
.bg-pink{background:var(--c-pink-bg)} .bg-blue{background:var(--c-blue-bg)}
.tx-cyan{color:var(--c-cyan)} .tx-purple{color:var(--c-purple)}
.tx-amber{color:var(--c-amber)} .tx-green{color:var(--c-green)}
.tx-pink{color:var(--c-pink)} .tx-blue{color:var(--c-blue)}

/* ---------- Branch (descriptive vs inferential) ---------- */
.branches { display: grid; grid-template-columns: 1fr 1fr; gap: 1.2rem; margin: 1.5rem 0; }
@media (max-width: 720px){ .branches { grid-template-columns: 1fr; } }
.branch {
  border-radius: 16px; padding: 1.6rem; border: 1px solid var(--line);
  background: var(--panel); position: relative; overflow: hidden;
}
.branch .btag {
  display: inline-flex; align-items: center; gap: 8px; font-weight: 800;
  font-size: 1.05rem; margin-bottom: 0.8rem;
}
.branch .bnum {
  width: 28px; height: 28px; border-radius: 8px; color: #fff; font-size: 0.85rem;
  display: flex; align-items: center; justify-content: center; font-weight: 800;
}
.branch ul { list-style: none; margin: 0.8rem 0 0; padding: 0; }
.branch li { font-size: 0.88rem; color: var(--ink-soft); padding: 0.35rem 0 0.35rem 1.5rem; position: relative; line-height: 1.5; }
.branch li::before { content: "▸"; position: absolute; left: 0; font-weight: 700; }
.branch.descr { border-top: 4px solid var(--c-cyan); }
.branch.descr li::before { color: var(--c-cyan); }
.branch.infer { border-top: 4px solid var(--c-purple); }
.branch.infer li::before { color: var(--c-purple); }

/* ---------- "Data → Insight → Action" strip ---------- */
.flow-strip { display: flex; align-items: stretch; gap: 0.5rem; margin: 1.5rem 0; flex-wrap: wrap; }
.flow-node {
  flex: 1; min-width: 150px; border-radius: 14px; padding: 1.3rem; text-align: center;
  color: #fff; position: relative;
}
.flow-node h4 { font-size: 1rem; margin-bottom: 0.3rem; }
.flow-node p { font-size: 0.8rem !important; color: rgba(255,255,255,0.85) !important; margin: 0 !important; line-height: 1.45 !important; }
.flow-arrow { display: flex; align-items: center; color: var(--ink-faint); font-size: 1.5rem; }
@media (max-width: 600px){ .flow-arrow{ transform: rotate(90deg); } }

/* ---------- Timeline ---------- */
.timeline { position: relative; margin: 1.8rem 0 0.5rem; padding-left: 0; }
.timeline::before {
  content: ""; position: absolute; left: 19px; top: 8px; bottom: 8px; width: 2px;
  background: linear-gradient(var(--c-cyan), var(--c-purple), var(--c-amber));
}
.tl-item { position: relative; padding: 0 0 1.4rem 3.2rem; }
.tl-dot {
  position: absolute; left: 10px; top: 2px; width: 20px; height: 20px; border-radius: 50%;
  background: #fff; border: 3px solid var(--c-purple); z-index: 1;
}
.tl-era { font-size: 0.74rem; font-weight: 800; letter-spacing: 0.06em; text-transform: uppercase; color: var(--c-purple); }
.tl-title { font-weight: 700; color: var(--ink); font-size: 0.98rem; margin: 1px 0 2px; }
.tl-desc { font-size: 0.85rem; color: var(--ink-soft); line-height: 1.5; }

/* ---------- Stats → ML bridge ---------- */
.bridge {
  background: linear-gradient(135deg, #0a1230 0%, #1a1452 100%); color: #fff;
  border-radius: 18px; padding: 2rem; margin: 1.5rem 0; position: relative; overflow: hidden;
}
.bridge::before{
  content:""; position:absolute; inset:0;
  background: radial-gradient(500px 200px at 80% 0%, rgba(0,212,255,0.18), transparent 60%);
}
.bridge-eq {
  position: relative; display: flex; align-items: center; justify-content: center;
  gap: 0.6rem; flex-wrap: wrap; margin-bottom: 1.6rem;
}
.eq-box {
  background: rgba(255,255,255,0.07); border: 1px solid rgba(255,255,255,0.15);
  border-radius: 12px; padding: 0.8rem 1rem; text-align: center; min-width: 96px;
}
.eq-box .ei { font-size: 1.5rem; }
.eq-box .el { font-size: 0.78rem; font-weight: 700; margin-top: 4px; }
.eq-box.highlight { background: rgba(0,212,255,0.16); border-color: rgba(0,212,255,0.5); }
.eq-op { font-size: 1.5rem; font-weight: 700; color: rgba(255,255,255,0.6); }

.map-card {
  background: var(--panel); border: 1px solid var(--line); border-radius: 14px;
  padding: 1.2rem; transition: all 0.25s ease;
}
.map-card:hover{ transform: translateY(-3px); box-shadow: 0 12px 28px rgba(20,30,80,0.10); }
.map-card .stat-side { font-size: 0.7rem; font-weight: 800; text-transform: uppercase; letter-spacing: 0.06em; color: var(--c-cyan); }
.map-card .arrow-down { color: var(--ink-faint); font-size: 1.1rem; margin: 2px 0; }
.map-card .ml-side { font-weight: 700; color: var(--ink); font-size: 0.95rem; }
.map-card p { font-size: 0.82rem !important; color: var(--ink-soft) !important; margin: 0.4rem 0 0 !important; line-height: 1.5 !important; }

/* ---------- Callout boxes ---------- */
.callout {
  display: flex; gap: 1rem; border-radius: 13px; padding: 1.2rem 1.4rem; margin: 1.4rem 0;
  border: 1px solid var(--line); background: var(--panel-2);
}
.callout .cico { font-size: 1.4rem; flex-shrink: 0; }
.callout .ctitle { font-weight: 700; color: var(--ink); margin-bottom: 0.25rem; font-size: 0.95rem; }
.callout p { margin: 0 !important; font-size: 0.88rem !important; color: var(--ink-soft) !important; line-height: 1.6 !important; }
.callout.tip { background: var(--c-green-bg); border-color: transparent; }
.callout.key { background: var(--c-amber-bg); border-color: transparent; }
.callout.note{ background: var(--c-blue-bg); border-color: transparent; }

/* ---------- Takeaways ---------- */
.takeaways {
  background: var(--panel); border: 1px solid var(--line); border-radius: 16px;
  padding: 1.6rem 1.8rem; box-shadow: 0 8px 30px rgba(20,30,80,0.05);
}
.takeaways h3 { font-size: 1.15rem; color: var(--ink); margin-bottom: 1rem; display: flex; align-items: center; gap: 10px; }
.takeaways ul { list-style: none; margin: 0; padding: 0; }
.takeaways li { display: flex; gap: 12px; padding: 0.55rem 0; font-size: 0.95rem; color: var(--ink-soft); line-height: 1.55; border-bottom: 1px dashed var(--line); }
.takeaways li:last-child { border-bottom: none; }
.takeaways li .ck { color: var(--c-green); flex-shrink: 0; font-weight: 800; }
/* .tick and .rw-find supply their own bullet via the .ck marker, so suppress the native list disc */
.tick, .rw-find, .step-list { list-style: none; }
/* Catch-all: any list item that carries its own .ck marker should not also show the native disc */
li:has(> .ck) { list-style: none; }

/* ---------- Notebook CTA ---------- */
.nb-cta {
  display: flex; align-items: center; gap: 1.3rem; flex-wrap: wrap;
  background: linear-gradient(135deg, #0a1230, #19134a); color: #fff;
  border-radius: 16px; padding: 1.6rem 1.8rem; margin: 1.5rem 0;
}
.nb-cta .nb-ic {
  width: 54px; height: 54px; border-radius: 13px; flex-shrink: 0;
  background: rgba(16,185,129,0.18); display: flex; align-items: center; justify-content: center; font-size: 1.6rem;
}
.nb-cta .nb-body { flex: 1; min-width: 220px; }
.nb-cta h3 { font-size: 1.1rem; margin-bottom: 0.25rem; }
.nb-cta p { font-size: 0.85rem !important; color: rgba(255,255,255,0.72) !important; margin: 0 !important; }
.nb-cta code { background: rgba(255,255,255,0.1); padding: 2px 7px; border-radius: 5px; font-size: 0.82rem; }

/* ---------- Chapter nav ---------- */
.chapter-nav { display: flex; justify-content: space-between; gap: 1rem; margin-top: 2.5rem; flex-wrap: wrap; }
.cn-btn {
  flex: 1; min-width: 200px; display: flex; align-items: center; gap: 12px;
  padding: 1.1rem 1.3rem; border-radius: 13px; border: 1px solid var(--line);
  background: var(--panel); transition: all 0.25s ease; text-decoration: none;
}
.cn-btn:hover { border-color: var(--c-purple); box-shadow: 0 8px 24px rgba(124,58,237,0.12); transform: translateY(-2px); }
.cn-btn .cn-dir { font-size: 0.72rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.08em; color: var(--ink-faint); }
.cn-btn .cn-title { font-weight: 700; color: var(--ink); font-size: 0.95rem; }
.cn-btn.next { text-align: right; justify-content: flex-end; }

/* SVG helpers */
svg .editable { /* marker class: these strokes/fills are safe to recolor */ }