:root {
  --bg: #f4f0e8;
  --paper: #fffdf8;
  --ink: #20242a;
  --muted: #66706c;
  --line: #d8d0c2;
  --teal: #0f766e;
  --teal-dark: #0b4f4a;
  --rust: #b45309;
  --sage: #60755d;
  --code-bg: #18201f;
  --code-ink: #edf7f3;
  --shadow: 0 18px 50px rgba(30, 38, 34, .10);
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  background:
    linear-gradient(90deg, rgba(15, 118, 110, .05) 1px, transparent 1px),
    linear-gradient(180deg, rgba(96, 117, 93, .05) 1px, transparent 1px),
    var(--bg);
  background-size: 42px 42px;
  color: var(--ink);
  font-family: Charter, "STSong", "Songti SC", Georgia, serif;
  line-height: 1.72;
}
a { color: var(--teal-dark); text-decoration: none; }
a:hover { color: var(--rust); }
.layout {
  display: grid;
  grid-template-columns: minmax(260px, 21vw) minmax(0, 1fr);
  min-height: 100vh;
}
.sidebar {
  position: sticky;
  top: 0;
  height: 100vh;
  overflow: auto;
  padding: 22px 18px;
  border-right: 1px solid var(--line);
  background: rgba(255, 253, 248, .9);
  backdrop-filter: blur(10px);
}
.brand { margin-bottom: 18px; padding-bottom: 16px; border-bottom: 1px solid var(--line); }
.brand-kicker {
  color: var(--rust);
  font: 700 12px/1.2 ui-monospace, SFMono-Regular, Menlo, monospace;
  letter-spacing: .08em;
  text-transform: uppercase;
}
.brand-title { margin: 8px 0 6px; font-size: 22px; font-weight: 850; line-height: 1.18; }
.brand-meta { color: var(--muted); font-size: 13px; line-height: 1.5; }
.search-box {
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 10px 11px;
  background: #fffaf0;
  color: var(--ink);
  font: 15px/1.4 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif;
  outline-color: var(--teal);
}
.filters {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 8px;
  margin: 12px 0 18px;
}
.filter-btn {
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 7px 8px;
  background: #fbf4e6;
  color: var(--muted);
  cursor: pointer;
  font: 700 12px/1.2 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif;
}
.filter-btn.active { border-color: var(--teal); background: var(--teal); color: white; }
.toc-group { margin: 18px 0; }
.toc-group-title {
  margin-bottom: 8px;
  color: var(--rust);
  font: 850 12px/1 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif;
}
.toc-link {
  display: block;
  padding: 7px 8px;
  border-radius: 7px;
  color: var(--muted);
  font: 14px/1.35 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif;
}
.toc-link:hover, .toc-link.current { background: rgba(15, 118, 110, .08); color: var(--teal-dark); }
.content {
  width: min(1180px, calc(100vw - 21vw));
  margin: 0 auto;
  padding: 36px 42px 80px;
}
.hero { padding: 48px 0 28px; border-bottom: 3px double var(--line); }
.hero h1 {
  max-width: 960px;
  margin: 0;
  font-size: clamp(38px, 5vw, 72px);
  line-height: .98;
  letter-spacing: 0;
}
.thesis { max-width: 920px; margin: 18px 0 0; color: #39413e; font-size: 20px; line-height: 1.7; }
.stats {
  display: grid;
  grid-template-columns: repeat(4, minmax(120px, 1fr));
  gap: 12px;
  margin-top: 28px;
}
.stat {
  padding: 15px 14px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: rgba(255, 253, 248, .82);
  box-shadow: var(--shadow);
}
.stat strong { display: block; font: 850 28px/1 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif; color: var(--teal-dark); }
.stat span { color: var(--muted); font: 13px/1.35 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif; }
.visual-lead {
  margin: 28px 0;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--paper);
  box-shadow: var(--shadow);
  overflow: hidden;
}
.visual-lead img { display: block; width: 100%; height: auto; }
.study-lanes, .chapter-grid, .formula-grid, .visual-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 12px;
  margin: 28px 0;
}
.chapter-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); margin-top: 24px; }
.lane, .chapter-card, .formula-card, .visual-card {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: rgba(255, 253, 248, .92);
  padding: 16px;
  box-shadow: var(--shadow);
}
.chapter-card {
  display: grid;
  grid-template-columns: 48px 1fr;
  gap: 10px;
  min-height: 86px;
}
.chapter-card:hover { transform: translateY(-1px); box-shadow: 0 22px 60px rgba(30, 38, 34, .14); }
.chapter-number {
  grid-row: span 3;
  color: var(--rust);
  font: 900 18px/1 ui-monospace, SFMono-Regular, Menlo, monospace;
}
.chapter-card-title { color: var(--ink); font: 850 15px/1.35 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif; }
.chapter-card-kind, .chapter-card-meta { color: var(--muted); font: 12px/1.35 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif; }
.chapter-page {
  margin: 0 0 42px;
  padding: 30px 34px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: rgba(255, 253, 248, .95);
  box-shadow: var(--shadow);
  overflow: hidden;
}
.chapter-nav {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  margin: 0 0 18px;
  font: 700 14px/1.4 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif;
}
.chapter-nav a {
  max-width: 48%;
  padding: 9px 12px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fffaf0;
}
.inline-enhancement {
  margin: 22px 0 28px;
  padding: 16px;
  border: 1px solid #b9d4cc;
  border-left: 4px solid var(--teal);
  border-radius: 8px;
  background: #f2fbf7;
}
.inline-enhancement-title {
  margin: 0 0 6px;
  font: 850 17px/1.35 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif;
  color: var(--teal-dark);
}
.inline-enhancement-note {
  margin: 0 0 12px;
  color: var(--muted);
  font-size: 14px;
}
.inline-enhancement .visual-grid {
  grid-template-columns: 1fr;
  margin: 12px 0;
}
.inline-enhancement .formula-grid {
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  margin: 12px 0 0;
}
.inline-enhancement.wide .visual-card img { max-height: none; }
.inline-enhancement.medium { max-width: 900px; }
.inline-enhancement.medium .visual-grid { max-width: 720px; }
.inline-enhancement.compact { max-width: 860px; }
.formula-card b, .visual-card b, .lane b {
  display: block;
  margin-bottom: 8px;
  font: 850 15px/1.2 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif;
}
.formula-card p, .visual-card p, .lane p { margin: 8px 0 0; color: var(--muted); font-size: 14px; }
.math-display {
  margin: 10px 0;
  padding: 10px;
  border-radius: 8px;
  background: white;
  overflow-x: auto;
}
.visual-card img { display: block; width: 100%; height: auto; border-radius: 6px; background: white; }
h1, h2, h3, h4, h5, h6 {
  font-family: ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif;
  letter-spacing: 0;
  line-height: 1.28;
}
h2 { margin: 0 0 20px; padding-bottom: 12px; border-bottom: 1px solid var(--line); font-size: 30px; }
h3 { margin: 34px 0 12px; font-size: 23px; color: var(--teal-dark); }
h4 { margin: 24px 0 10px; font-size: 18px; color: #4b5b50; }
h5, h6 { margin: 20px 0 8px; font-size: 15px; color: var(--rust); }
.anchor-link { float: right; margin-left: 10px; opacity: .22; font: 700 14px/1 ui-monospace, SFMono-Regular, Menlo, monospace; }
h2:hover .anchor-link, h3:hover .anchor-link, h4:hover .anchor-link { opacity: 1; }
p { margin: 12px 0; }
ul, ol { padding-left: 1.35rem; }
li { margin: 6px 0; }
code {
  padding: 2px 5px;
  border-radius: 5px;
  background: #ece5d7;
  color: #7c2d12;
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  font-size: .92em;
}
pre {
  margin: 16px 0;
  padding: 16px;
  border-radius: 8px;
  background: var(--code-bg);
  color: var(--code-ink);
  overflow: auto;
  tab-size: 2;
}
pre code { padding: 0; background: transparent; color: inherit; font-size: 13px; line-height: 1.58; }
.table-wrap {
  width: 100%;
  overflow-x: auto;
  margin: 16px 0;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: white;
}
table { width: 100%; min-width: 620px; border-collapse: collapse; font-family: ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif; font-size: 14px; line-height: 1.55; }
th, td { padding: 10px 12px; border-bottom: 1px solid #e7dfd2; vertical-align: top; }
th { background: #efe7d8; color: #2f3633; text-align: left; font-weight: 850; }
tr:nth-child(even) td { background: #fffaf0; }
blockquote { margin: 16px 0; padding: 8px 16px; border-left: 4px solid var(--sage); background: #f1f6ec; color: #435044; }
hr { border: 0; border-top: 1px solid var(--line); margin: 28px 0; }
.footer { margin-top: 56px; padding-top: 22px; border-top: 1px solid var(--line); color: var(--muted); font: 13px/1.6 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif; }
.mobile-tools { display: none; position: sticky; top: 0; z-index: 3; padding: 10px; border-bottom: 1px solid var(--line); background: rgba(255, 253, 248, .95); backdrop-filter: blur(10px); }
@media (max-width: 980px) {
  .layout { display: block; }
  .sidebar { position: static; height: auto; max-height: none; border-right: 0; border-bottom: 1px solid var(--line); }
  .content { width: 100%; padding: 18px 16px 64px; }
  .stats, .study-lanes, .chapter-grid, .formula-grid, .visual-grid { grid-template-columns: 1fr; }
  .chapter-page { padding: 22px 16px; }
  .hero h1 { font-size: 42px; }
  .mobile-tools { display: block; }
}
@media print {
  body { background: white; }
  .sidebar, .mobile-tools, .chapter-grid, .study-lanes, .chapter-nav { display: none; }
  .layout { display: block; }
  .content { width: auto; padding: 0; }
  .chapter-page { page-break-inside: avoid; box-shadow: none; border: 1px solid #bbb; }
  a { color: black; }
}