:root {
  --bg: #f6f7f4;
  --paper: #ffffff;
  --ink: #162022;
  --muted: #647170;
  --line: #d9e0dc;
  --teal: #006a6a;
  --teal-dark: #034b4d;
  --blue: #2d5f9a;
  --green: #4d7b42;
  --amber: #b46b20;
  --red: #b6473d;
  --soft-teal: #e8f3f0;
  --soft-blue: #eaf0f8;
  --soft-amber: #fbf0df;
  --soft-green: #eef5e9;
  --shadow: 0 18px 45px rgba(25, 35, 35, 0.10);
  --radius: 8px;
  --mono: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  --sans: Inter, "SF Pro Text", "PingFang SC", "Microsoft YaHei", "Noto Sans CJK SC", Arial, sans-serif;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  color: var(--ink);
  background:
    linear-gradient(90deg, rgba(0, 106, 106, 0.06) 0 1px, transparent 1px 100%) 0 0 / 44px 44px,
    linear-gradient(0deg, rgba(45, 95, 154, 0.05) 0 1px, transparent 1px 100%) 0 0 / 44px 44px,
    var(--bg);
  font-family: var(--sans);
  line-height: 1.78;
  letter-spacing: 0;
  -webkit-touch-callout: none;
  -webkit-user-select: none;
  user-select: none;
}

a {
  color: var(--teal-dark);
  text-decoration-thickness: 1px;
  text-underline-offset: 3px;
}

img,
svg {
  max-width: 100%;
}

.page-shell {
  display: grid;
  grid-template-columns: 286px minmax(0, 1fr);
  min-height: 100vh;
}

.sidebar {
  position: sticky;
  top: 0;
  height: 100vh;
  padding: 24px 18px;
  border-right: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.88);
  backdrop-filter: blur(14px);
  overflow: auto;
}

.brand {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 22px;
  color: var(--teal-dark);
  text-decoration: none;
}

.brand-mark {
  display: grid;
  width: 42px;
  height: 42px;
  place-items: center;
  border: 2px solid var(--teal);
  border-radius: var(--radius);
  color: var(--teal-dark);
  font-weight: 900;
  font-size: 18px;
}

.brand-title {
  display: block;
  font-size: 17px;
  font-weight: 850;
  line-height: 1.2;
}

.brand-subtitle {
  display: block;
  color: var(--muted);
  font-size: 12px;
}

.nav-group {
  margin: 22px 0;
}

.nav-label {
  margin: 0 0 9px;
  color: var(--muted);
  font-size: 12px;
  font-weight: 800;
  text-transform: uppercase;
}

.nav-link {
  display: flex;
  align-items: center;
  gap: 10px;
  min-height: 40px;
  padding: 8px 10px;
  border: 1px solid transparent;
  border-radius: var(--radius);
  color: var(--ink);
  text-decoration: none;
  font-size: 14px;
  line-height: 1.35;
}

.nav-link:hover,
.nav-link.active {
  border-color: rgba(0, 106, 106, 0.25);
  background: var(--soft-teal);
  color: var(--teal-dark);
}

.nav-number {
  display: inline-grid;
  flex: 0 0 24px;
  width: 24px;
  height: 24px;
  place-items: center;
  border-radius: 50%;
  background: #eef2ef;
  color: var(--teal-dark);
  font-size: 12px;
  font-weight: 850;
}

.sidebar-note {
  margin-top: 22px;
  padding: 12px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fbfcfa;
  color: var(--muted);
  font-size: 13px;
}

.content {
  min-width: 0;
  max-width: 100vw;
  overflow-x: hidden;
  padding: 30px clamp(18px, 4vw, 56px) 72px;
}

.top-strip {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  margin-bottom: 26px;
}

.crumb {
  color: var(--muted);
  font-size: 14px;
}

.hero {
  display: grid;
  grid-template-columns: minmax(0, 1.15fr) minmax(300px, 0.85fr);
  align-items: center;
  gap: 26px;
  margin-bottom: 28px;
  padding: clamp(24px, 4vw, 42px);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--paper);
  box-shadow: var(--shadow);
}

.hero h1 {
  margin: 0 0 14px;
  font-size: clamp(32px, 4.4vw, 56px);
  line-height: 1.06;
  letter-spacing: 0;
}

.hero p {
  max-width: 760px;
  margin: 0 0 18px;
  color: #40504f;
  font-size: 17px;
}

.eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 14px;
  color: var(--amber);
  font-size: 13px;
  font-weight: 900;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 42px;
  padding: 9px 14px;
  border: 1px solid var(--teal);
  border-radius: var(--radius);
  background: var(--teal);
  color: #fff;
  font-weight: 800;
  text-decoration: none;
}

.button.secondary {
  background: #fff;
  color: var(--teal-dark);
}

.visual-card {
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fbfcfa;
}

.visual-caption {
  padding: 10px 12px;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 13px;
}

.study-figure {
  overflow: hidden;
  margin: 16px 0;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fbfcfa;
}

.study-figure .diagram {
  display: block;
  width: 100%;
  max-height: 330px;
}

.study-figure figcaption {
  padding: 10px 12px;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 13px;
  line-height: 1.5;
}

.grid {
  display: grid;
  gap: 16px;
}

.grid.two {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.grid.three {
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.grid.four {
  grid-template-columns: repeat(4, minmax(0, 1fr));
}

.card {
  padding: 20px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--paper);
  box-shadow: 0 8px 22px rgba(25, 35, 35, 0.06);
}

.card h2,
.card h3,
.card h4 {
  margin-top: 0;
}

.chapter-card {
  display: grid;
  min-height: 100%;
  grid-template-rows: auto 1fr auto;
  gap: 12px;
}

.chapter-card .tag {
  justify-self: start;
}

.tag {
  display: inline-flex;
  align-items: center;
  min-height: 26px;
  padding: 3px 8px;
  border: 1px solid rgba(0, 106, 106, 0.22);
  border-radius: var(--radius);
  background: var(--soft-teal);
  color: var(--teal-dark);
  font-size: 12px;
  font-weight: 850;
}

.tag.blue {
  border-color: rgba(45, 95, 154, 0.22);
  background: var(--soft-blue);
  color: var(--blue);
}

.tag.amber {
  border-color: rgba(180, 107, 32, 0.24);
  background: var(--soft-amber);
  color: var(--amber);
}

.tag.green {
  border-color: rgba(77, 123, 66, 0.24);
  background: var(--soft-green);
  color: var(--green);
}

.section {
  margin: 34px 0;
}

.section > h2 {
  margin: 0 0 14px;
  font-size: clamp(24px, 3vw, 34px);
  line-height: 1.2;
}

.section > p.lead,
.lead {
  max-width: 900px;
  color: #40504f;
  font-size: 17px;
}

.callout {
  margin: 18px 0;
  padding: 16px 18px;
  border-left: 5px solid var(--teal);
  border-radius: var(--radius);
  background: var(--soft-teal);
}

.callout.warning {
  border-left-color: var(--amber);
  background: var(--soft-amber);
}

.callout.check {
  border-left-color: var(--green);
  background: var(--soft-green);
}

.formula {
  margin: 14px 0;
  padding: 13px 16px;
  border: 1px solid #d3ddd8;
  border-radius: var(--radius);
  background: #fbfcfa;
  font-family: var(--mono);
  font-size: 15px;
  line-height: 1.7;
  overflow-x: auto;
}

.formula strong {
  color: var(--teal-dark);
}

.steps {
  counter-reset: step;
  display: grid;
  gap: 12px;
  margin: 16px 0;
}

.step {
  position: relative;
  padding: 15px 16px 15px 54px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--paper);
}

.step::before {
  counter-increment: step;
  content: counter(step);
  position: absolute;
  top: 15px;
  left: 16px;
  display: grid;
  width: 26px;
  height: 26px;
  place-items: center;
  border-radius: 50%;
  background: var(--teal);
  color: #fff;
  font-size: 13px;
  font-weight: 900;
}

.example {
  border: 1px solid #cfdad5;
  border-radius: var(--radius);
  background: var(--paper);
}

.example + .example {
  margin-top: 16px;
}

.example-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 14px;
  padding: 14px 16px;
  border-bottom: 1px solid var(--line);
  background: #fbfcfa;
}

.example-title {
  margin: 0;
  font-size: 18px;
}

.example-body {
  padding: 16px;
}

details.answer {
  margin-top: 12px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fbfcfa;
}

details.answer summary {
  padding: 10px 12px;
  cursor: pointer;
  color: var(--teal-dark);
  font-weight: 850;
}

details.answer .answer-content {
  padding: 0 12px 12px;
}

.table-wrap {
  overflow-x: auto;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--paper);
}

table {
  width: 100%;
  border-collapse: collapse;
  min-width: 680px;
}

th,
td {
  padding: 12px 14px;
  border-bottom: 1px solid var(--line);
  text-align: left;
  vertical-align: top;
}

th {
  background: #eef3ef;
  color: var(--teal-dark);
  font-size: 14px;
}

tr:last-child td {
  border-bottom: 0;
}

.checklist {
  display: grid;
  gap: 8px;
}

.check-item {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  padding: 10px 12px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--paper);
}

.check-item input {
  margin-top: 7px;
  accent-color: var(--teal);
}

.mini {
  color: var(--muted);
  font-size: 13px;
}

.source-list {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: 12px 0 0;
}

.source-list a {
  display: inline-flex;
  align-items: center;
  min-height: 30px;
  padding: 4px 9px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fff;
  text-decoration: none;
  font-size: 13px;
}

.timeline {
  position: relative;
  display: grid;
  gap: 12px;
}

.timeline::before {
  content: "";
  position: absolute;
  top: 0;
  bottom: 0;
  left: 17px;
  width: 2px;
  background: var(--line);
}

.timeline-item {
  position: relative;
  padding: 14px 16px 14px 52px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--paper);
}

.timeline-item::before {
  content: "";
  position: absolute;
  top: 18px;
  left: 9px;
  width: 18px;
  height: 18px;
  border: 4px solid var(--paper);
  border-radius: 50%;
  background: var(--teal);
  box-shadow: 0 0 0 1px var(--line);
}

.diagram {
  display: block;
  width: 100%;
  height: auto;
  background: #fbfcfa;
}

.diagram text {
  font-family: var(--sans);
  fill: var(--ink);
  paint-order: stroke fill;
  stroke: #fbfcfa;
  stroke-width: 5px;
  stroke-linejoin: round;
}

.diagram .muted {
  fill: var(--muted);
}

.diagram .teal {
  fill: var(--teal);
}

.diagram .blue {
  fill: var(--blue);
}

.diagram .green {
  fill: var(--green);
}

.diagram .amber {
  fill: var(--amber);
}

.diagram .red {
  fill: var(--red);
}

.diagram .stroke-teal {
  stroke: var(--teal);
}

.diagram .stroke-blue {
  stroke: var(--blue);
}

.diagram .stroke-green {
  stroke: var(--green);
}

.diagram .stroke-amber {
  stroke: var(--amber);
}

.diagram .stroke-red {
  stroke: var(--red);
}

.diagram .thin {
  stroke-width: 2;
}

.diagram .thick {
  stroke-width: 6;
}

.footer-nav {
  display: flex;
  justify-content: space-between;
  gap: 14px;
  margin-top: 44px;
}

.footer-nav a {
  flex: 1;
  padding: 14px 16px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--paper);
  text-decoration: none;
}

.footer-nav a:last-child {
  text-align: right;
}

.kbd {
  padding: 1px 6px;
  border: 1px solid #cfd8d4;
  border-bottom-width: 2px;
  border-radius: 5px;
  background: #fff;
  font-family: var(--mono);
  font-size: 12px;
}

.progress-bar {
  height: 8px;
  overflow: hidden;
  border-radius: 999px;
  background: #e8ece9;
}

.progress-bar span {
  display: block;
  width: 0;
  height: 100%;
  background: var(--teal);
  color: transparent;
  transition: width 0.2s ease;
}

.exam-hero {
  border-top: 6px solid var(--teal);
}

.chapter-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: 16px 0 0;
}

.exam-objectives {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 12px;
  margin-top: 18px;
}

.objective {
  padding: 14px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fbfcfa;
}

.objective strong {
  display: block;
  margin-bottom: 4px;
  color: var(--teal-dark);
}

.math-display {
  max-width: 100%;
  margin: 14px 0;
  padding: 14px 16px;
  border: 1px solid #d3ddd8;
  border-radius: var(--radius);
  background: #fbfcfa;
  overflow-x: auto;
  overflow-y: hidden;
}

.math-display .katex-display {
  margin: 0.25em 0;
  overflow-x: auto;
  overflow-y: hidden;
  padding-bottom: 2px;
}

.math-display .katex-html {
  max-width: 100%;
}

.katex .katex-mathml {
  display: none !important;
}

.formula-note {
  margin-top: 8px;
  color: var(--muted);
  font-size: 14px;
}

.exam-note {
  display: grid;
  grid-template-columns: 44px minmax(0, 1fr);
  gap: 12px;
  align-items: start;
  margin: 16px 0;
  padding: 14px;
  border: 1px solid rgba(180, 107, 32, 0.24);
  border-radius: var(--radius);
  background: var(--soft-amber);
}

.exam-note .mark {
  display: grid;
  width: 36px;
  height: 36px;
  place-items: center;
  border-radius: 50%;
  background: #fff;
  color: var(--amber);
  font-weight: 900;
}

.worked {
  margin: 18px 0;
  border: 1px solid #cfdad5;
  border-radius: var(--radius);
  background: var(--paper);
  box-shadow: 0 8px 22px rgba(25, 35, 35, 0.05);
}

.worked-head {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 12px;
  padding: 14px 16px;
  border-bottom: 1px solid var(--line);
  background: #fbfcfa;
}

.worked-head h3 {
  margin: 0;
  font-size: 19px;
  line-height: 1.35;
}

.worked-body {
  padding: 16px;
}

.scene-brief {
  margin: 0 0 12px;
  padding: 11px 13px;
  border: 1px solid rgba(45, 95, 154, 0.2);
  border-left: 5px solid var(--blue);
  border-radius: var(--radius);
  background: var(--soft-blue);
  color: var(--ink);
  line-height: 1.72;
}

.scene-brief strong {
  color: var(--blue);
}

.method-steps {
  margin: 12px 0 14px;
  padding: 12px 14px;
  border: 1px solid rgba(0, 106, 106, 0.2);
  border-left: 5px solid var(--teal);
  border-radius: var(--radius);
  background: var(--soft-teal);
}

.method-steps strong {
  color: var(--teal-dark);
}

.method-steps ol {
  margin: 8px 0 0;
  padding-left: 24px;
}

.method-steps li {
  margin: 4px 0;
  line-height: 1.65;
}

.solution {
  margin-top: 14px;
  padding: 14px 16px;
  border-left: 5px solid var(--green);
  border-radius: var(--radius);
  background: var(--soft-green);
}

.solution h4 {
  margin: 0 0 8px;
  color: var(--green);
}

.mistakes {
  margin: 14px 0 0;
  padding: 12px 14px;
  border: 1px solid rgba(182, 71, 61, 0.22);
  border-radius: var(--radius);
  background: #fff1ef;
}

.mistakes strong {
  color: var(--red);
}

.question-grid {
  display: grid;
  gap: 14px;
}

.question {
  padding: 15px 16px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--paper);
}

.question h3 {
  margin: 0 0 8px;
  font-size: 18px;
}

.answer summary {
  list-style-position: inside;
}

.derivation {
  display: grid;
  gap: 10px;
}

.derivation-row {
  padding: 10px 12px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fff;
}

.exam-bank-list {
  counter-reset: exam;
  display: grid;
  gap: 14px;
}

.exam-bank-item {
  counter-increment: exam;
  position: relative;
  padding: 16px 16px 16px 56px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--paper);
}

.exam-bank-item::before {
  content: counter(exam);
  position: absolute;
  top: 16px;
  left: 16px;
  display: grid;
  width: 28px;
  height: 28px;
  place-items: center;
  border-radius: 50%;
  background: var(--teal);
  color: #fff;
  font-weight: 900;
}

.tier-block {
  margin: 22px 0;
  padding: 18px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fbfcfa;
}

.tier-block > h3 {
  margin: 0 0 6px;
  font-size: 20px;
}

.tier-block > p {
  margin: 0 0 14px;
  color: var(--muted);
}

.tier-list {
  display: grid;
  gap: 14px;
}

.tier-example {
  padding: 14px;
  border: 1px solid #cfdad5;
  border-radius: var(--radius);
  background: var(--paper);
}

.tier-head {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  gap: 10px;
  align-items: start;
  margin-bottom: 10px;
}

.tier-head h3 {
  margin: 0;
  font-size: 17px;
  line-height: 1.45;
}

.level-badge {
  display: inline-flex;
  align-items: center;
  min-height: 28px;
  padding: 3px 9px;
  border-radius: var(--radius);
  background: var(--soft-teal);
  color: var(--teal-dark);
  font-size: 12px;
  font-weight: 900;
}

.toc-list {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 10px;
}

.toc-list a {
  padding: 12px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fff;
  text-decoration: none;
}

.mobile-nav {
  display: none;
  margin-bottom: 18px;
}

.mobile-nav select {
  width: 100%;
  padding: 10px 12px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--paper);
  font: inherit;
}

@media (max-width: 1040px) {
  .page-shell {
    grid-template-columns: 1fr;
  }

  .sidebar {
    display: none;
  }

  .mobile-nav {
    display: block;
  }

  .hero {
    grid-template-columns: 1fr;
  }

  .grid.three,
  .grid.four {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .exam-objectives,
  .toc-list {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 720px) {
  body {
    background: var(--bg);
  }

  .content {
    padding: 18px 14px 50px;
  }

  .top-strip {
    align-items: flex-start;
    flex-direction: column;
  }

  .hero {
    padding: 20px;
  }

  .grid.two,
  .grid.three,
  .grid.four {
    grid-template-columns: 1fr;
  }

  .footer-nav {
    flex-direction: column;
  }

  .footer-nav a:last-child {
    text-align: left;
  }
}

@media print {
  html,
  body {
    background: #fff;
  }

  body::before {
    content: "本资料不提供打印或导出 PDF。";
    display: block;
    margin: 20vh auto 0;
    max-width: 620px;
    padding: 28px;
    border: 1px solid #d9e0dc;
    border-radius: 8px;
    color: #102124;
    font: 700 22px/1.5 system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
    text-align: center;
  }

  .page-shell {
    display: none !important;
  }
}