:root {
  --ink: #172033;
  --muted: #596273;
  --navy: #003366;
  --gold: #d4af37;
  --terra: #b85c38;
  --brown: #8b7355;
  --paper: #fffdf8;
  --line: #e3e7ec;
  --soft: #f3f6fa;
  --white: #ffffff;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  color: var(--ink);
  background: var(--white);
  font-family: "Inter", system-ui, sans-serif;
  line-height: 1.75;
}
a { color: var(--navy); text-decoration-thickness: 1px; text-underline-offset: 3px; }
img { max-width: 100%; height: auto; }
.shell { width: min(1160px, calc(100% - 40px)); margin: 0 auto; }
.reading-shell { width: min(780px, calc(100% - 40px)); margin: 0 auto; }
.brand-elephant { color: var(--terra); }
.brand-dot { color: var(--gold); }
.brand-tech { color: var(--brown); }

.site-header {
  position: sticky;
  top: 0;
  z-index: 20;
  background: rgba(255,255,255,.96);
  border-bottom: 1px solid var(--line);
  backdrop-filter: blur(14px);
}
.header-inner { min-height: 76px; display: flex; align-items: center; justify-content: space-between; }
.brand { display: flex; align-items: center; gap: 12px; font-weight: 800; letter-spacing: .04em; text-decoration: none; }
.brand img { display: block; width: 45px; }
.site-nav { display: flex; align-items: center; gap: 28px; }
.site-nav a { color: var(--ink); font-weight: 700; text-decoration: none; }
.site-nav a:hover, .site-nav a[aria-current="page"] { color: var(--gold); }
.site-nav .nav-cta { color: white; background: var(--navy); border-radius: 8px; padding: 10px 16px; }
.menu-toggle { display: none; font: inherit; font-weight: 700; background: white; border: 1px solid var(--line); border-radius: 7px; padding: 8px 12px; }

.book-hero {
  overflow: hidden;
  background:
    radial-gradient(circle at 80% 20%, rgba(212,175,55,.20), transparent 28rem),
    linear-gradient(145deg, #eef4fb, #ffffff 62%);
  border-bottom: 1px solid var(--line);
}
.hero-grid { display: grid; grid-template-columns: 1.25fr .75fr; gap: 70px; align-items: center; padding: 80px 0; }
.hero-copy h1 {
  margin: 10px 0 24px;
  color: var(--navy);
  font-size: clamp(3rem, 7vw, 5.9rem);
  line-height: .98;
  letter-spacing: -.055em;
}
.eyebrow { margin: 0 0 12px; color: var(--terra); font-size: .82rem; font-weight: 800; letter-spacing: .12em; text-transform: uppercase; }
.lead { max-width: 760px; color: var(--muted); font-size: 1.22rem; line-height: 1.7; }
.hero-actions, .chapter-actions { display: flex; flex-wrap: wrap; gap: 12px; margin-top: 30px; }
.button {
  display: inline-flex;
  justify-content: center;
  align-items: center;
  min-height: 48px;
  padding: 11px 20px;
  border: 2px solid var(--navy);
  border-radius: 8px;
  font-weight: 800;
  text-decoration: none;
  cursor: pointer;
}
.button.primary { color: white; background: var(--navy); }
.button.secondary { color: var(--navy); background: white; }
.button.full { width: 100%; }
.cover-wrap { perspective: 1000px; text-align: center; }
.cover-wrap img {
  width: min(100%, 390px);
  border: 1px solid rgba(0,0,0,.08);
  box-shadow: 0 28px 60px rgba(0,36,71,.24);
  transform: rotateY(-4deg) rotateX(1deg);
}
.share-panel { display: flex; flex-wrap: wrap; align-items: center; gap: 10px; margin-top: 24px; font-size: .9rem; }
.share-panel span { font-weight: 800; color: var(--muted); }
.share-panel a, .share-panel button {
  color: var(--navy);
  background: white;
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 6px 11px;
  font: inherit;
  font-weight: 700;
  text-decoration: none;
  cursor: pointer;
}

.intro-section, .book-cta { padding: 86px 0; }
.intro-section h2, .contents-section h2, .book-cta h2 { margin: 0 0 22px; color: var(--navy); font-size: clamp(2rem, 4vw, 3.2rem); line-height: 1.12; letter-spacing: -.035em; }
.intro-section p, .book-cta p { color: var(--muted); font-size: 1.08rem; }
.audience-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 18px; margin-top: 36px; }
.audience-grid div { padding: 24px; background: var(--soft); border: 1px solid var(--line); border-radius: 12px; }
.audience-grid strong, .audience-grid span { display: block; }
.audience-grid strong { color: var(--navy); margin-bottom: 8px; }
.audience-grid span { color: var(--muted); font-size: .92rem; }

.contents-section { padding: 86px 0; background: var(--soft); border-block: 1px solid var(--line); }
.section-heading { max-width: 760px; margin-bottom: 38px; }
.section-heading p:last-child { color: var(--muted); font-size: 1.05rem; }
.chapter-list { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 14px; }
.part-heading { grid-column: 1 / -1; margin: 34px 0 4px; color: var(--terra); font-size: 1rem; letter-spacing: .08em; text-transform: uppercase; }
.part-heading:first-child { margin-top: 0; }
.chapter-card {
  display: grid;
  grid-template-columns: 48px 1fr 24px;
  gap: 15px;
  align-items: start;
  min-height: 145px;
  padding: 22px;
  color: var(--ink);
  background: white;
  border: 1px solid var(--line);
  border-radius: 12px;
  text-decoration: none;
  transition: transform .18s ease, box-shadow .18s ease, border-color .18s ease;
}
.chapter-card:hover { transform: translateY(-3px); border-color: var(--gold); box-shadow: 0 12px 28px rgba(0,51,102,.08); }
.card-number { display: grid; place-items: center; width: 42px; height: 42px; color: white; background: var(--navy); border-radius: 50%; font-weight: 900; }
.chapter-card strong { display: block; color: var(--navy); font-size: 1.06rem; line-height: 1.35; }
.chapter-card small { display: block; margin-top: 8px; color: var(--muted); font-size: .86rem; line-height: 1.55; }
.card-arrow { color: var(--gold); font-size: 1.3rem; font-weight: 900; }
.book-cta { text-align: center; background: var(--paper); }
.centered { justify-content: center; }

.chapter-hero { padding: 68px 0 58px; background: linear-gradient(145deg, #eef4fb, white); border-bottom: 1px solid var(--line); }
.breadcrumbs { display: flex; flex-wrap: wrap; gap: 8px; margin-bottom: 36px; color: var(--muted); font-size: .86rem; }
.breadcrumbs a { color: var(--muted); }
.part-label { margin: 0; color: var(--terra); font-weight: 800; text-transform: uppercase; letter-spacing: .1em; font-size: .82rem; }
.chapter-number { margin: 14px 0 2px; color: var(--gold); font-size: 1.05rem; font-weight: 900; text-transform: uppercase; }
.chapter-hero h1 { margin: 5px 0 18px; color: var(--navy); font-size: clamp(2.4rem, 6vw, 4.3rem); line-height: 1.03; letter-spacing: -.045em; }
.chapter-description { max-width: 720px; margin: 0; color: var(--muted); font-size: 1.14rem; }
.reading-layout { display: grid; grid-template-columns: minmax(0, 780px) 270px; gap: 64px; align-items: start; padding-block: 72px 92px; }
.book-article { min-width: 0; }
.book-article h2 { margin: 58px 0 18px; color: var(--navy); font-size: clamp(1.65rem, 3vw, 2.3rem); line-height: 1.2; letter-spacing: -.025em; }
.book-article h2:first-child { margin-top: 0; }
.book-article h3 { margin: 36px 0 12px; color: var(--terra); font-size: .9rem; letter-spacing: .08em; }
.book-article p { margin: 0 0 22px; color: #283142; font-size: 1.02rem; }
.book-list { margin: 0 0 28px; padding-left: 24px; }
.book-list li { margin: 0 0 12px; padding-left: 4px; }
.figure-caption { padding-left: 14px; border-left: 3px solid var(--gold); color: var(--muted) !important; font-size: .88rem !important; font-style: italic; }
.book-data {
  overflow-x: auto;
  margin: 22px 0 28px;
  padding: 18px;
  color: #172033;
  background: var(--soft);
  border: 1px solid var(--line);
  border-radius: 9px;
  font: 500 .82rem/1.65 ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  white-space: pre-wrap;
}
.book-sidebar { position: sticky; top: 100px; padding: 20px; background: var(--paper); border: 1px solid var(--line); border-radius: 12px; }
.book-sidebar img { display: block; margin-bottom: 18px; border: 1px solid var(--line); box-shadow: 0 12px 28px rgba(0,36,71,.14); }
.book-sidebar p { color: var(--muted); font-size: .88rem; line-height: 1.55; }
.book-sidebar .share-panel { align-items: flex-start; }
.chapter-nav { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; margin-top: 70px; padding-top: 28px; border-top: 1px solid var(--line); }
.chapter-nav a { font-weight: 800; text-decoration: none; }
.chapter-nav a:last-child { text-align: right; }

.site-footer { color: #dce5ee; background: #101d2c; padding-top: 54px; }
.footer-grid { display: grid; grid-template-columns: 2fr 1fr 1.2fr; gap: 50px; }
.footer-grid > div { display: flex; flex-direction: column; gap: 8px; }
.footer-grid a, .footer-grid span { color: #dce5ee; font-size: .9rem; }
.footer-grid p { max-width: 390px; color: #aab7c4; }
.footer-brand { font-size: 1.08rem; font-weight: 900; letter-spacing: .04em; }
.copyright { margin-top: 40px; padding: 22px 0; border-top: 1px solid rgba(255,255,255,.12); color: #91a0ae; font-size: .82rem; }

@media (max-width: 900px) {
  .hero-grid, .reading-layout { grid-template-columns: 1fr; }
  .hero-grid { gap: 50px; }
  .cover-wrap { order: -1; }
  .cover-wrap img { width: min(70vw, 330px); transform: none; }
  .book-sidebar { position: static; display: grid; grid-template-columns: 130px 1fr; gap: 16px; }
  .book-sidebar img { grid-row: 1 / 4; }
  .book-sidebar .share-panel { grid-column: 1 / -1; }
  .audience-grid { grid-template-columns: 1fr; }
}

@media (max-width: 760px) {
  .shell, .reading-shell { width: min(100% - 28px, 780px); }
  .menu-toggle { display: block; }
  .site-nav {
    display: none;
    position: absolute;
    inset: 76px 14px auto;
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    padding: 12px;
    background: white;
    border: 1px solid var(--line);
    border-radius: 10px;
    box-shadow: 0 16px 32px rgba(0,0,0,.14);
  }
  .site-nav.open { display: flex; }
  .site-nav a { padding: 12px; }
  .brand > span { display: none; }
  .hero-grid { padding: 54px 0; }
  .hero-copy h1 { font-size: clamp(2.8rem, 14vw, 4.2rem); }
  .chapter-list { grid-template-columns: 1fr; }
  .chapter-card { min-height: 0; }
  .book-sidebar { display: block; }
  .book-sidebar img { width: 180px; margin-inline: auto; }
  .chapter-nav { grid-template-columns: 1fr; }
  .chapter-nav a:last-child { text-align: left; }
  .footer-grid { grid-template-columns: 1fr; }
}