:root {
  --bg: #f3f5f2;
  --paper: #fffefb;
  --ink: #1f2528;
  --muted: #63706d;
  --line: #d5ddd5;
  --teal: #0f766e;
  --teal-dark: #0b4f4a;
  --rust: #a34416;
  --indigo: #284b7a;
  --sage: #5f755f;
  --soft-blue: #eef4fa;
  --soft-green: #eff8f4;
  --code-bg: #17201e;
  --code-ink: #eef8f4;
  --shadow: 0 18px 46px rgba(31, 37, 40, .09);
}
* { 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(40, 75, 122, .045) 1px, transparent 1px),
    var(--bg);
  background-size: 44px 44px;
  color: var(--ink);
  font-family: Charter, "STSong", "Songti SC", Georgia, serif;
  line-height: 1.74;
}
a { color: var(--teal-dark); text-decoration: none; }
a:hover { color: var(--rust); }
.layout { display: grid; grid-template-columns: minmax(270px, 22vw) 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, 254, 251, .92);
  backdrop-filter: blur(10px);
}
.brand { margin-bottom: 18px; padding-bottom: 16px; border-bottom: 1px solid var(--line); }
.brand-kicker {
  color: var(--rust);
  font: 800 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: #fffefb;
  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: #f7f9f5;
  color: var(--muted);
  cursor: pointer;
  font: 800 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/1.25 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 - 22vw)); margin: 0 auto; padding: 36px 42px 80px; }
.hero { padding: 48px 0 28px; border-bottom: 3px double var(--line); }
.hero h1 { max-width: 980px; margin: 0; font-size: clamp(38px, 5vw, 70px); line-height: 1; letter-spacing: 0; }
.thesis { max-width: 920px; margin: 18px 0 0; color: #384240; 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, 254, 251, .86); 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; }
.logic-overview { display: grid; grid-template-columns: minmax(0, 1.05fr) minmax(320px, .95fr); gap: 18px; margin: 28px 0; padding: 20px; border: 1px solid var(--line); border-left: 4px solid var(--teal); border-radius: 8px; background: rgba(255, 254, 251, .92); box-shadow: var(--shadow); }
.logic-copy h2 { margin: 0 0 10px; padding: 0; border: 0; font-size: 24px; }
.logic-copy p { margin: 0; color: #39413e; }
.logic-steps { display: grid; gap: 10px; }
.logic-steps div { display: grid; grid-template-columns: 96px 1fr; gap: 10px; padding: 10px 12px; border: 1px solid #dce7e1; border-radius: 8px; background: var(--soft-green); }
.logic-steps b { color: var(--teal-dark); font: 850 13px/1.4 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif; }
.logic-steps span { color: var(--muted); font: 13px/1.5 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif; }
.study-lanes, .chapter-grid, .concept-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, .concept-card { border: 1px solid var(--line); border-radius: 8px; background: rgba(255, 254, 251, .94); padding: 16px; box-shadow: var(--shadow); }
.chapter-card { display: grid; grid-template-columns: 48px 1fr; gap: 10px; min-height: 88px; }
.chapter-card:hover { transform: translateY(-1px); box-shadow: 0 22px 58px rgba(31, 37, 40, .13); }
.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-sections { margin: 30px 0; }
.chapter-section { margin: 30px 0 36px; }
.chapter-section-heading { display: grid; grid-template-columns: minmax(220px, .34fr) minmax(0, 1fr); gap: 18px; align-items: start; margin-bottom: 12px; padding-bottom: 10px; border-bottom: 1px solid var(--line); }
.chapter-section-heading span { color: var(--teal-dark); font: 900 20px/1.25 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif; }
.chapter-section-heading p { margin: 0; color: var(--muted); font: 14px/1.65 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, 254, 251, .96); 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: #fffefb; }
.chapter-orientation { margin: 0 0 24px; padding: 15px 16px; border: 1px solid #d7e6df; border-left: 4px solid var(--teal); border-radius: 8px; background: var(--soft-green); }
.chapter-orientation b { display: block; margin-bottom: 6px; color: var(--teal-dark); font: 850 15px/1.35 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif; }
.chapter-orientation p { margin: 0; color: #4b5b50; font: 14px/1.65 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif; }
.next-step {
  margin: -8px 0 24px;
  padding: 12px 14px;
  border: 1px solid #c7d6e8;
  border-left: 4px solid var(--indigo);
  border-radius: 8px;
  background: var(--soft-blue);
}
.next-step b {
  display: block;
  margin-bottom: 5px;
  color: var(--indigo);
  font: 850 14px/1.35 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif;
}
.next-step p {
  margin: 0;
  color: #4b5564;
  font: 14px/1.62 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif;
}
.question-columns { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 12px; margin: 18px 0; }
.question-column { border: 1px solid var(--line); border-radius: 8px; background: #fff; padding: 12px 15px; }
.question-column h4 { margin-top: 0; }
.concept-card b, .lane b { display: block; margin-bottom: 8px; font: 850 15px/1.2 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif; }
.concept-card p, .lane p { margin: 8px 0 0; color: var(--muted); font-size: 14px; }
.math-display {
  margin: 14px 0;
  padding: 12px 14px;
  border-radius: 8px;
  background: white;
  overflow-x: auto;
  overflow-y: hidden;
  border: 1px solid #edf0eb;
}
.math-display mjx-container[jax="CHTML"][display="true"] {
  margin: 0;
  max-width: 100%;
  overflow-x: auto;
  overflow-y: hidden;
}
mjx-container {
  max-width: 100%;
  overflow-x: auto;
  overflow-y: hidden;
}
.formula-list {
  display: grid;
  gap: 10px;
  margin: 18px 0;
}
.formula-list div {
  display: grid;
  grid-template-columns: minmax(120px, .22fr) minmax(0, 1fr);
  gap: 14px;
  align-items: start;
  padding: 12px 14px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: white;
}
.formula-list b {
  color: var(--teal-dark);
  font: 850 14px/1.4 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif;
}
.formula-list span {
  min-width: 0;
  overflow-x: auto;
}
.checkpoint-list {
  padding: 14px 18px 14px 36px;
  border: 1px solid #d7e6df;
  border-radius: 8px;
  background: var(--soft-green);
}
.worked-example {
  margin: 18px 0 26px;
  padding: 18px;
  border: 1px solid var(--line);
  border-left: 4px solid var(--indigo);
  border-radius: 8px;
  background: rgba(255, 254, 251, .98);
  box-shadow: var(--shadow);
}
.example-title {
  margin-bottom: 8px;
  color: var(--indigo);
  font: 850 13px/1.35 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif;
}
.solution {
  margin-top: 14px;
  padding: 14px 15px;
  border: 1px solid #d7e6df;
  border-radius: 8px;
  background: var(--soft-green);
}
.intuition-box {
  margin-top: 14px;
  padding: 13px 15px;
  border: 1px solid #e8c7aa;
  border-radius: 8px;
  background: #fff7ed;
}
.intuition-box b {
  display: block;
  margin-bottom: 5px;
  color: var(--rust);
  font: 850 14px/1.35 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif;
}
.intuition-box p {
  margin: 0;
  color: #5d4b40;
}
.algorithm-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 12px;
  margin: 18px 0 26px;
}
.algorithm-card {
  min-width: 0;
  padding: 15px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: rgba(255, 254, 251, .96);
  box-shadow: var(--shadow);
}
.algorithm-card h4 {
  margin: 0 0 10px;
  color: var(--teal-dark);
}
.algorithm-card p {
  margin: 8px 0;
  color: #46524f;
  font-size: 14px;
  line-height: 1.58;
}
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; }
.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 { opacity: 1; }
p { margin: 12px 0; }
ul, ol { padding-left: 1.35rem; }
li { margin: 6px 0; }
code { padding: 2px 5px; border-radius: 5px; background: #e8eee8; color: #7c2d12; font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace; font-size: .92em; }
.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: 680px; 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 #e4ebe4; vertical-align: top; }
th { background: #eef4ee; color: #2f3633; text-align: left; font-weight: 850; }
tr:nth-child(even) td { background: #fbfdfb; }
blockquote { margin: 16px 0; padding: 8px 16px; border-left: 4px solid var(--sage); background: #f1f6ec; color: #435044; }
.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, 254, 251, .95); backdrop-filter: blur(10px); }
.no-results { display: none; padding: 16px; border: 1px solid var(--line); border-radius: 8px; background: white; color: var(--muted); font: 14px/1.6 ui-sans-serif, "PingFang SC", "Microsoft YaHei", sans-serif; }
@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, .concept-grid, .question-columns, .algorithm-grid { grid-template-columns: 1fr; }
  .formula-list div { grid-template-columns: 1fr; }
  .chapter-page { padding: 22px 16px; }
  .hero h1 { font-size: 42px; }
  .logic-overview { grid-template-columns: 1fr; }
  .chapter-section-heading { grid-template-columns: 1fr; gap: 6px; }
  .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; }
}