/* ============================================================
   资料分析 · 速算站 / 第二讲
   纸质底 + 墨色 + 朱砂，编辑排版式的学习站
   ============================================================ */

:root {
  --paper: #f5f1e7;
  --paper-2: #efe9da;
  --card: #fbf8f1;
  --ink: #1b211e;
  --ink-2: #3d4641;
  --muted: #5c645c;
  --faint: #687068;
  --line: rgba(27, 33, 30, 0.13);
  --line-strong: rgba(27, 33, 30, 0.28);
  --accent: #c4452c;
  --accent-2: #a83622;
  --accent-soft: #f2ddd4;
  --teal: #2e6b5e;
  --teal-soft: #e2ece7;
  --gold: #b08734;
  --sidebar: #18211d;
  --sidebar-2: #111815;
  --sidebar-text: #ece5d6;
  --serif: "Songti SC", "Noto Serif SC", "Source Han Serif SC", "STSong", "SimSun", serif;
  --sans: "PingFang SC", "Microsoft YaHei", "Noto Sans SC", "Segoe UI", system-ui, sans-serif;
  --mono: "DIN Alternate", "Bahnschrift", "Consolas", "SFMono-Regular", monospace;
  --shadow: 0 1px 0 rgba(27, 33, 30, 0.04), 0 18px 40px -30px rgba(27, 33, 30, 0.55);
  --radius: 3px;
}

* { box-sizing: border-box; }

.skip-link { z-index: 200; padding: 8px 14px; color: var(--card); background: var(--ink); }
.skip-link:focus { left: 12px !important; top: 12px; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background-color: var(--paper);
  background-image:
    radial-gradient(rgba(27, 33, 30, 0.045) 0.7px, transparent 0.7px),
    repeating-linear-gradient(0deg, transparent 0, transparent 63px, rgba(27, 33, 30, 0.022) 64px);
  background-size: 22px 22px, 100% 64px;
  color: var(--ink);
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.8;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

::selection { background: var(--accent); color: #fff; }

a { color: inherit; text-decoration: none; }

button, input { font: inherit; color: inherit; }

button { cursor: pointer; }

:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 3px;
}

/* ---------- 布局 ---------- */

.app { min-height: 100vh; }

.sidebar {
  position: fixed;
  inset: 0 auto 0 0;
  z-index: 50;
  display: flex;
  width: 276px;
  flex-direction: column;
  padding: 26px 22px 20px;
  overflow-y: auto;
  color: var(--sidebar-text);
  background:
    linear-gradient(180deg, rgba(255, 255, 255, 0.035), transparent 30%),
    repeating-linear-gradient(0deg, transparent 0, transparent 47px, rgba(255, 255, 255, 0.032) 48px),
    var(--sidebar);
  border-right: 1px solid rgba(0, 0, 0, 0.4);
  transition: transform 0.35s cubic-bezier(0.22, 1, 0.36, 1);
}

.sidebar::-webkit-scrollbar { width: 5px; }
.sidebar::-webkit-scrollbar-thumb { background: rgba(255, 255, 255, 0.16); }

.sidebar-close {
  display: none;
  position: absolute;
  top: 18px;
  right: 16px;
  width: 32px;
  height: 32px;
  color: rgba(236, 229, 214, 0.6);
  font-size: 20px;
  line-height: 1;
  background: transparent;
  border: 1px solid rgba(255, 255, 255, 0.16);
  border-radius: 50%;
}
.sidebar-close:hover { color: #fff; border-color: rgba(255, 255, 255, 0.4); }

.brand {
  display: flex;
  align-items: center;
  gap: 12px;
  padding-bottom: 22px;
  border-bottom: 1px solid rgba(255, 255, 255, 0.12);
}

.seal {
  display: grid;
  width: 38px;
  height: 38px;
  flex: 0 0 38px;
  place-items: center;
  color: #f6e8da;
  font-family: var(--serif);
  font-size: 19px;
  line-height: 1;
  background: var(--accent);
  box-shadow: inset 0 0 0 2px rgba(255, 255, 255, 0.22);
}

.brand-copy small {
  display: block;
  color: rgba(236, 229, 214, 0.55);
  font-family: var(--mono);
  font-size: 9px;
  letter-spacing: 0.24em;
  text-transform: uppercase;
}

.brand-copy strong {
  display: block;
  margin-top: 2px;
  font-family: var(--serif);
  font-size: 17px;
  font-weight: 600;
  letter-spacing: 0.06em;
}

.lesson-card {
  position: relative;
  margin: 22px 0 20px;
  padding: 18px 16px 16px;
  background: rgba(255, 255, 255, 0.045);
  border: 1px solid rgba(255, 255, 255, 0.09);
}

.lesson-card .kicker {
  color: rgba(236, 229, 214, 0.5);
  font-family: var(--mono);
  font-size: 9px;
  letter-spacing: 0.2em;
}

.lesson-card h2 {
  margin: 6px 0 14px;
  font-family: var(--serif);
  font-size: 19px;
  font-weight: 600;
  line-height: 1.45;
  letter-spacing: 0.02em;
}

.progress-row {
  display: flex;
  align-items: center;
  gap: 14px;
}

.ring { position: relative; width: 58px; height: 58px; flex: 0 0 58px; }
.ring svg { display: block; width: 100%; height: 100%; transform: rotate(-90deg); }
.ring .track { fill: none; stroke: rgba(255, 255, 255, 0.12); stroke-width: 3; }
.ring .bar {
  fill: none;
  stroke: #e8c9a8;
  stroke-width: 3;
  stroke-linecap: round;
  transition: stroke-dasharray 0.6s cubic-bezier(0.22, 1, 0.36, 1);
}
.ring b {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
  font-family: var(--mono);
  font-size: 13px;
  font-weight: 600;
  letter-spacing: -0.02em;
}
.ring b small { font-size: 9px; opacity: 0.5; }

.progress-copy { font-size: 11px; line-height: 1.6; color: rgba(236, 229, 214, 0.55); }
.progress-copy strong { display: block; color: var(--sidebar-text); font-size: 13px; font-weight: 500; }

.nav { display: flex; flex-direction: column; gap: 2px; margin-top: 4px; }

.nav-label {
  margin: 14px 0 6px;
  color: rgba(236, 229, 214, 0.55);
  font-family: var(--mono);
  font-size: 9px;
  letter-spacing: 0.22em;
}

.nav a {
  position: relative;
  display: flex;
  align-items: baseline;
  gap: 10px;
  padding: 8px 10px;
  color: rgba(236, 229, 214, 0.68);
  font-size: 13px;
  line-height: 1.45;
  border-radius: 2px;
  transition: color 0.2s, background 0.2s;
}

.nav a .idx {
  width: 18px;
  flex: 0 0 18px;
  color: rgba(236, 229, 214, 0.32);
  font-family: var(--mono);
  font-size: 9px;
  letter-spacing: 0.04em;
}

.nav a:hover { color: var(--sidebar-text); background: rgba(255, 255, 255, 0.055); }

.nav a.active {
  color: #fff9ec;
  background: rgba(196, 69, 44, 0.2);
  box-shadow: inset 2px 0 0 var(--accent);
}
.nav a.active .idx { color: #e8c9a8; }

.nav a .due-dot {
  width: 5px;
  height: 5px;
  margin-left: auto;
  align-self: center;
  background: #e0a35e;
  border-radius: 50%;
  box-shadow: 0 0 0 3px rgba(224, 163, 94, 0.14);
}

.sidebar-foot {
  margin-top: auto;
  padding-top: 20px;
  color: rgba(236, 229, 214, 0.58);
  font-size: 10px;
  line-height: 1.7;
  border-top: 1px solid rgba(255, 255, 255, 0.08);
}
.sidebar-foot a { color: rgba(236, 229, 214, 0.55); border-bottom: 1px solid rgba(255, 255, 255, 0.18); }
.sidebar-foot a:hover { color: #fff; }

.main { display: flex; min-height: 100vh; flex-direction: column; margin-left: 276px; }

.topbar {
  position: sticky;
  top: 0;
  z-index: 30;
  display: flex;
  min-height: 62px;
  align-items: center;
  gap: 16px;
  padding: 0 40px;
  background: rgba(245, 241, 231, 0.86);
  border-bottom: 1px solid var(--line);
  backdrop-filter: blur(14px);
}

.crumb {
  display: flex;
  align-items: center;
  gap: 8px;
  overflow: hidden;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.09em;
  white-space: nowrap;
}
.crumb b { color: var(--ink); font-weight: 500; }
.crumb i { font-style: normal; color: var(--faint); }

.top-actions { display: flex; align-items: center; gap: 10px; margin-left: auto; }

.menu-btn {
  display: none;
  padding: 7px;
  background: none;
  border: 1px solid var(--line);
  border-radius: 2px;
}
.menu-btn span { display: block; width: 16px; height: 1px; margin: 3px 0; background: var(--ink); }

.view {
  width: min(1040px, calc(100% - 88px));
  margin: 0 auto;
  padding: 46px 0 92px;
  flex: 1;
}

.scrim {
  position: fixed;
  inset: 0;
  z-index: 45;
  background: rgba(17, 24, 21, 0.55);
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.3s;
}
.scrim.show { opacity: 1; pointer-events: auto; }

/* ---------- 通用排版 ---------- */

.eyebrow {
  display: flex;
  align-items: center;
  gap: 10px;
  color: var(--accent);
  font-family: var(--mono);
  font-size: 10px;
  font-weight: 600;
  letter-spacing: 0.22em;
  text-transform: uppercase;
}
.eyebrow::before { content: ""; width: 26px; height: 1px; background: var(--accent); }

h1, h2, h3, h4 { margin: 0; font-family: var(--serif); font-weight: 700; letter-spacing: 0.01em; }

.lead { color: var(--ink-2); font-size: 16.5px; line-height: 1.95; }

.mono { font-family: var(--mono); font-variant-numeric: tabular-nums; }

.dim { color: var(--muted); }

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 9px;
  min-height: 44px;
  padding: 0 20px;
  color: #faf6ec;
  font-size: 13px;
  font-weight: 500;
  letter-spacing: 0.04em;
  background: var(--ink);
  border: 1px solid var(--ink);
  border-radius: 2px;
  transition: transform 0.18s, background 0.18s, color 0.18s, border-color 0.18s;
}
.btn:hover { transform: translateY(-1px); background: #2a332e; }
.btn .arrow { transition: transform 0.18s; }
.btn:hover .arrow { transform: translateX(3px); }

.btn-accent { background: var(--accent); border-color: var(--accent); }
.btn-accent:hover { background: var(--accent-2); }

.btn-ghost {
  color: var(--ink);
  background: transparent;
  border-color: var(--line-strong);
}
.btn-ghost:hover { background: rgba(27, 33, 30, 0.05); }

.btn-sm { min-height: 34px; padding: 0 13px; font-size: 12px; }

.btn:disabled { opacity: 0.45; cursor: not-allowed; transform: none; }

.chip {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 9px;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.04em;
  border: 1px solid var(--line);
  border-radius: 999px;
}

.tag {
  display: inline-block;
  padding: 2px 7px;
  color: var(--accent-2);
  font-family: var(--mono);
  font-size: 9px;
  letter-spacing: 0.08em;
  background: var(--accent-soft);
  border-radius: 1px;
}

.section-title {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  gap: 20px;
  margin: 52px 0 8px;
  padding-bottom: 12px;
  border-bottom: 1px solid var(--line);
}
.section-title h2 { font-size: 26px; }
.section-title .note { color: var(--muted); font-family: var(--mono); font-size: 10px; letter-spacing: 0.1em; }

/* ---------- 首页 hero ---------- */

.hero {
  position: relative;
  display: grid;
  grid-template-columns: minmax(0, 1.45fr) minmax(250px, 0.55fr);
  gap: 48px;
  padding: 18px 0 42px;
  border-bottom: 1px solid var(--line);
}

.hero-copy { position: relative; z-index: 1; }

.hero h1 {
  max-width: 660px;
  margin: 20px 0 22px;
  font-size: clamp(46px, 5.6vw, 78px);
  font-weight: 700;
  line-height: 1.08;
  letter-spacing: -0.035em;
}
.hero h1 .lesson-no {
  display: block;
  margin-bottom: 10px;
  color: var(--accent);
  font-family: var(--mono);
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.3em;
  -webkit-text-stroke: 0;
}
.hero h1 .thin { color: var(--muted); font-weight: 400; }

.hero-lead { max-width: 590px; font-size: 16px; }

.hero-meta { display: flex; flex-wrap: wrap; gap: 8px; margin: 24px 0 28px; }

.hero-actions { display: flex; flex-wrap: wrap; align-items: center; gap: 12px; }

.hero-side {
  position: relative;
  display: flex;
  min-height: 340px;
  flex-direction: column;
  justify-content: flex-end;
  gap: 14px;
}

.hero-num {
  position: absolute;
  top: -48px;
  right: -12px;
  z-index: 0;
  color: transparent;
  font-family: var(--serif);
  font-size: 210px;
  font-weight: 700;
  line-height: 1;
  letter-spacing: -0.08em;
  -webkit-text-stroke: 1px rgba(27, 33, 30, 0.16);
  pointer-events: none;
  user-select: none;
}

.quote-card {
  position: relative;
  z-index: 1;
  padding: 24px 22px 20px;
  color: #f4ecdd;
  background: var(--sidebar);
  border-radius: 2px;
  box-shadow: var(--shadow);
}
.quote-card::before {
  content: "“";
  position: absolute;
  top: -20px;
  left: 14px;
  color: var(--accent);
  font-family: var(--serif);
  font-size: 80px;
  line-height: 1;
  opacity: 0.85;
}
.quote-card p {
  position: relative;
  margin: 8px 0 14px;
  font-family: var(--serif);
  font-size: 21px;
  line-height: 1.55;
  letter-spacing: 0.02em;
}
.quote-card small {
  display: block;
  color: rgba(244, 236, 221, 0.48);
  font-family: var(--mono);
  font-size: 9px;
  letter-spacing: 0.16em;
}

.formula-slip {
  position: relative;
  z-index: 1;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 13px 16px;
  background: var(--card);
  border: 1px solid var(--line);
  box-shadow: var(--shadow);
}
.formula-slip .math { font-family: var(--serif); font-size: 17px; }
.formula-slip span:last-child { color: var(--faint); font-family: var(--mono); font-size: 9px; letter-spacing: 0.12em; }

.stats {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  border-bottom: 1px solid var(--line);
}
.stat { padding: 22px 20px 22px 0; border-right: 1px solid var(--line); }
.stat:last-child { border-right: 0; }
.stat + .stat { padding-left: 24px; }
.stat b {
  display: block;
  font-family: var(--serif);
  font-size: 30px;
  font-weight: 700;
  line-height: 1.2;
  letter-spacing: -0.02em;
}
.stat small {
  display: block;
  margin-top: 4px;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 9px;
  letter-spacing: 0.14em;
}

/* ---------- 首页模块 ---------- */

.split {
  display: grid;
  grid-template-columns: minmax(0, 1.55fr) minmax(260px, 0.45fr);
  gap: 42px;
  align-items: start;
}

.path-list { margin-top: 8px; }

.path-row {
  display: grid;
  grid-template-columns: 52px minmax(0, 1fr) auto;
  gap: 18px;
  align-items: center;
  padding: 20px 0;
  border-bottom: 1px solid var(--line);
  transition: padding 0.2s, background 0.2s;
}
.path-row:hover { padding-left: 8px; }
.path-row .no {
  color: var(--faint);
  font-family: var(--serif);
  font-size: 26px;
  line-height: 1;
}
.path-row h3 { font-size: 19px; font-weight: 600; }
.path-row .sub {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 4px;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 9.5px;
  letter-spacing: 0.05em;
}
.path-row .go { color: var(--muted); transition: transform 0.2s, color 0.2s; }
.path-row:hover .go { color: var(--accent); transform: translateX(4px); }

.mini-track {
  height: 2px;
  margin-top: 12px;
  overflow: hidden;
  background: var(--line);
}
.mini-track i {
  display: block;
  height: 100%;
  background: var(--teal);
  transition: width 0.5s;
}

.side-card {
  padding: 22px;
  background: var(--card);
  border: 1px solid var(--line);
  box-shadow: var(--shadow);
}
.side-card h3 { margin-bottom: 6px; font-size: 18px; }
.side-card .sub { color: var(--muted); font-size: 12px; line-height: 1.7; }
.side-card + .side-card { margin-top: 16px; }

.due-list { margin: 14px 0 0; padding: 0; list-style: none; }
.due-item {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 10px 0;
  border-top: 1px solid var(--line);
}
.due-item .due-main { min-width: 0; flex: 1; }
.due-item a { display: block; overflow: hidden; font-size: 13px; text-overflow: ellipsis; white-space: nowrap; }
.due-item a:hover { color: var(--accent); }
.due-item small { color: var(--muted); font-family: var(--mono); font-size: 9px; }
.due-item button {
  flex: 0 0 auto;
  padding: 4px 8px;
  color: var(--teal);
  font-size: 10px;
  background: var(--teal-soft);
  border: 0;
  border-radius: 2px;
}
.due-item button:hover { background: #d3e4dc; }

.empty-note {
  margin-top: 12px;
  padding: 14px 0 0;
  color: var(--muted);
  font-size: 12px;
  line-height: 1.75;
  border-top: 1px solid var(--line);
}

.principle-list { margin: 12px 0 0; padding: 0; list-style: none; counter-reset: p; }
.principle-list li {
  position: relative;
  padding: 9px 0 9px 30px;
  color: var(--ink-2);
  font-size: 13px;
  line-height: 1.7;
  border-top: 1px solid var(--line);
  counter-increment: p;
}
.principle-list li::before {
  content: counter(p, decimal-leading-zero);
  position: absolute;
  left: 0;
  top: 11px;
  color: var(--accent);
  font-family: var(--mono);
  font-size: 9px;
}

/* ---------- 章节页 ---------- */

.section-hero {
  position: relative;
  padding: 22px 0 36px;
  overflow: hidden;
  border-bottom: 1px solid var(--line);
}
.section-hero .section-no {
  position: absolute;
  top: -34px;
  right: 0;
  color: transparent;
  font-family: var(--serif);
  font-size: 164px;
  font-weight: 700;
  line-height: 1;
  letter-spacing: -0.06em;
  -webkit-text-stroke: 1px rgba(27, 33, 30, 0.14);
  pointer-events: none;
  user-select: none;
}
.section-hero h1 {
  position: relative;
  margin: 16px 0 14px;
  font-size: clamp(34px, 4vw, 52px);
  line-height: 1.2;
  letter-spacing: -0.02em;
}
.section-hero .lead { position: relative; max-width: 700px; }
.section-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 20px;
}

.takeaways {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1px;
  margin: 30px 0 6px;
  background: var(--line);
  border: 1px solid var(--line);
}
.takeaway {
  position: relative;
  min-height: 132px;
  padding: 20px 20px 18px;
  background: var(--card);
}
.takeaway::before {
  content: attr(data-n);
  display: block;
  margin-bottom: 10px;
  color: var(--accent);
  font-family: var(--mono);
  font-size: 9px;
  letter-spacing: 0.14em;
}
.takeaway p { margin: 0; font-family: var(--serif); font-size: 16px; line-height: 1.7; }

/* ---------- 考点卡 ---------- */

.kp {
  position: relative;
  margin: 22px 0;
  scroll-margin-top: 84px;
  padding: 28px 32px 22px;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  opacity: 0;
  transform: translateY(14px);
  transition: opacity 0.55s ease, transform 0.55s cubic-bezier(0.22, 1, 0.36, 1), border-color 0.2s;
}
.kp.in { opacity: 1; transform: none; }
.kp:hover { border-color: var(--line-strong); }
.kp::before {
  content: "";
  position: absolute;
  top: 30px;
  bottom: 30px;
  left: -1px;
  width: 2px;
  background: var(--accent);
  opacity: 0.9;
}
.kp.is-mastered::before { background: var(--teal); }
.kp.is-mastered { background: linear-gradient(180deg, rgba(46, 107, 94, 0.028), transparent 120px), var(--card); }

.kp-head {
  display: flex;
  align-items: flex-start;
  gap: 15px;
  padding-right: 118px;
}
.kp-index {
  width: 40px;
  flex: 0 0 40px;
  padding-top: 3px;
  color: var(--faint);
  font-family: var(--serif);
  font-size: 26px;
  line-height: 1;
}
.kp-title-wrap { min-width: 0; }
.kp h3 {
  margin-top: 5px;
  font-size: 24px;
  line-height: 1.4;
  letter-spacing: 0.005em;
}
.kp-badges { display: flex; flex-wrap: wrap; align-items: center; gap: 7px; }

.master-btn {
  position: absolute;
  top: 26px;
  right: 28px;
  display: inline-flex;
  align-items: center;
  gap: 7px;
  padding: 6px 10px;
  color: var(--muted);
  font-size: 11px;
  background: transparent;
  border: 1px solid var(--line);
  border-radius: 999px;
  transition: color 0.2s, border-color 0.2s, background 0.2s;
}
.master-btn:hover { color: var(--ink); border-color: var(--line-strong); }
.master-btn .dot {
  width: 7px;
  height: 7px;
  border: 1px solid currentColor;
  border-radius: 50%;
}
.master-btn[aria-pressed="true"] {
  color: var(--teal);
  background: var(--teal-soft);
  border-color: rgba(46, 107, 94, 0.35);
}
.master-btn[aria-pressed="true"] .dot {
  background: var(--teal);
  border-color: var(--teal);
  box-shadow: inset 0 0 0 1.5px var(--teal-soft);
}

.kp-gist {
  margin: 18px 0 16px;
  padding: 13px 18px;
  color: var(--ink);
  font-family: var(--serif);
  font-size: 18px;
  line-height: 1.75;
  background: rgba(176, 135, 52, 0.065);
  border-left: 2px solid var(--gold);
}
.kp-gist::before {
  content: "一句话";
  display: inline-block;
  margin-right: 10px;
  padding: 1px 6px;
  color: var(--gold);
  font-family: var(--mono);
  font-size: 9px;
  letter-spacing: 0.08em;
  vertical-align: 2px;
  border: 1px solid rgba(176, 135, 52, 0.4);
  border-radius: 1px;
}

.kp-points { margin: 0; padding: 0; list-style: none; }
.kp-points li {
  position: relative;
  padding: 7px 0 7px 20px;
  color: var(--ink-2);
  font-size: 15px;
  line-height: 1.8;
}
.kp-points li::before {
  content: "";
  position: absolute;
  top: 17px;
  left: 2px;
  width: 6px;
  height: 6px;
  background: var(--accent);
  opacity: 0.7;
  transform: rotate(45deg);
}

.formula-box {
  margin: 16px 0;
  padding: 15px 20px;
  overflow-x: auto;
  color: #f4ecdd;
  background: var(--sidebar);
  border-radius: 1px;
}
.formula-box .math { font-family: var(--serif); font-size: 19px; line-height: 2; }
.formula-box .formula + .formula { margin-top: 4px; }
.formula-box .formula::before {
  content: "式";
  display: inline-block;
  margin-right: 12px;
  color: rgba(244, 236, 221, 0.32);
  font-family: var(--mono);
  font-size: 8px;
  letter-spacing: 0.1em;
  vertical-align: 3px;
  border: 1px solid rgba(244, 236, 221, 0.22);
  padding: 1px 4px;
}

.example {
  margin: 16px 0;
  background: rgba(27, 33, 30, 0.024);
  border: 1px solid var(--line);
}
.example summary {
  display: flex;
  align-items: center;
  gap: 9px;
  padding: 11px 16px;
  color: var(--ink-2);
  font-size: 12px;
  font-weight: 500;
  letter-spacing: 0.02em;
  cursor: pointer;
  list-style: none;
  user-select: none;
}
.example summary::-webkit-details-marker { display: none; }
.example summary::before {
  content: "例";
  display: grid;
  width: 19px;
  height: 19px;
  flex: 0 0 19px;
  place-items: center;
  color: var(--card);
  font-family: var(--serif);
  font-size: 11px;
  background: var(--ink);
  border-radius: 50%;
}
.example summary::after {
  content: "+";
  margin-left: auto;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 15px;
}
.example[open] summary::after { content: "−"; }
.example .example-body { padding: 2px 18px 16px 44px; }
.example .example-body p { margin: 4px 0; color: var(--ink-2); font-size: 14px; line-height: 1.8; }
.example .example-answer {
  display: inline-block;
  margin-top: 8px;
  padding: 2px 9px;
  color: var(--teal);
  font-size: 12px;
  background: var(--teal-soft);
  border-radius: 2px;
}

.traps-box {
  margin: 18px 0 0;
  padding: 15px 18px 12px;
  background: rgba(196, 69, 44, 0.045);
  border: 1px dashed rgba(196, 69, 44, 0.32);
}
.traps-box h4 {
  display: flex;
  align-items: center;
  gap: 7px;
  margin-bottom: 6px;
  color: var(--accent-2);
  font-family: var(--sans);
  font-size: 10px;
  font-weight: 600;
  letter-spacing: 0.16em;
}
.traps-box h4::before {
  content: "!";
  display: grid;
  width: 14px;
  height: 14px;
  place-items: center;
  color: #fff;
  font-family: var(--mono);
  font-size: 9px;
  background: var(--accent);
  border-radius: 50%;
}
.traps-box ul { margin: 0; padding: 0; list-style: none; }
.traps-box li {
  position: relative;
  padding: 5px 0 5px 15px;
  color: #6f3a2e;
  font-size: 13px;
  line-height: 1.75;
}
.traps-box li::before {
  content: "—";
  position: absolute;
  left: 0;
  color: rgba(196, 69, 44, 0.5);
}

.kp-foot {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 10px 18px;
  margin-top: 18px;
  padding-top: 13px;
  color: var(--faint);
  font-family: var(--mono);
  font-size: 9.5px;
  letter-spacing: 0.05em;
  border-top: 1px solid var(--line);
}
.kp-foot .target { color: var(--accent); }
.kp-foot a { margin-left: auto; color: var(--muted); border-bottom: 1px solid var(--line); }
.kp-foot a:hover { color: var(--accent); border-color: var(--accent); }

.pager {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  margin-top: 40px;
  padding-top: 22px;
  border-top: 1px solid var(--line);
}
.pager a {
  display: flex;
  flex-direction: column;
  gap: 3px;
  padding: 10px 0;
  color: var(--muted);
  font-size: 12px;
}
.pager a:hover { color: var(--accent); }
.pager a small { font-family: var(--mono); font-size: 9px; letter-spacing: 0.1em; }
.pager a.next { text-align: right; margin-left: auto; }

/* ---------- 易错清单 ---------- */

.page-hero { padding: 14px 0 32px; border-bottom: 1px solid var(--line); }
.page-hero h1 { margin: 16px 0 12px; font-size: clamp(36px, 4.4vw, 56px); line-height: 1.18; letter-spacing: -0.025em; }
.page-hero .lead { max-width: 720px; }

.filter-bar {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin: 26px 0 6px;
}
.filter-bar button {
  padding: 5px 11px;
  color: var(--muted);
  font-size: 11px;
  background: transparent;
  border: 1px solid var(--line);
  border-radius: 999px;
  transition: all 0.18s;
}
.filter-bar button:hover { color: var(--ink); border-color: var(--line-strong); }
.filter-bar button.active { color: var(--card); background: var(--ink); border-color: var(--ink); }

.trap-card {
  margin: 16px 0;
  padding: 22px 24px;
  background: var(--card);
  border: 1px solid var(--line);
  border-left: 2px solid rgba(196, 69, 44, 0.65);
}
.trap-card header { display: flex; align-items: baseline; gap: 10px; }
.trap-card h3 { font-size: 18px; }
.trap-card .count { margin-left: auto; color: var(--faint); font-family: var(--mono); font-size: 9px; }
.trap-card ol { margin: 10px 0 0; padding: 0 0 0 0; list-style: none; counter-reset: t; }
.trap-card li {
  position: relative;
  padding: 7px 0 7px 28px;
  color: var(--ink-2);
  font-size: 14px;
  line-height: 1.75;
  border-top: 1px solid var(--line);
  counter-increment: t;
}
.trap-card li::before {
  content: counter(t, decimal-leading-zero);
  position: absolute;
  left: 0;
  top: 10px;
  color: var(--accent);
  font-family: var(--mono);
  font-size: 9px;
}

/* ---------- 速查 ---------- */

.cheat-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; margin-top: 24px; }
.cheat-card {
  padding: 24px;
  background: var(--card);
  border: 1px solid var(--line);
  box-shadow: var(--shadow);
}
.cheat-card.wide { grid-column: 1 / -1; }
.cheat-card h3 { display: flex; align-items: baseline; gap: 10px; margin-bottom: 12px; font-size: 20px; }
.cheat-card h3 small { color: var(--faint); font-family: var(--mono); font-size: 9px; font-weight: 400; letter-spacing: 0.1em; }

.decision-list { margin: 0; padding: 0; list-style: none; counter-reset: d; }
.decision-list li {
  display: grid;
  grid-template-columns: 150px minmax(0, 1fr);
  gap: 14px;
  padding: 11px 0;
  border-top: 1px solid var(--line);
  counter-increment: d;
}
.decision-list .q { color: var(--ink); font-size: 13px; font-weight: 600; }
.decision-list .a { color: var(--ink-2); font-size: 13px; line-height: 1.75; }

.fraction-grid {
  display: grid;
  grid-template-columns: repeat(6, 1fr);
  gap: 1px;
  overflow: hidden;
  background: var(--line);
  border: 1px solid var(--line);
}
.fraction-cell {
  display: flex;
  flex-direction: column;
  gap: 2px;
  padding: 11px 8px;
  text-align: center;
  background: var(--card);
  transition: background 0.18s;
}
.fraction-cell:hover { background: var(--paper-2); }
.fraction-cell b { font-family: var(--mono); font-size: 13px; font-weight: 600; }
.fraction-cell span { color: var(--accent); font-family: var(--serif); font-size: 14px; }

.data-table { width: 100%; border-collapse: collapse; font-size: 13px; }
.data-table th {
  padding: 8px 10px;
  color: var(--faint);
  font-family: var(--mono);
  font-size: 9px;
  font-weight: 500;
  letter-spacing: 0.09em;
  text-align: left;
  border-bottom: 1px solid var(--line-strong);
}
.data-table td { padding: 10px; color: var(--ink-2); line-height: 1.7; border-bottom: 1px solid var(--line); vertical-align: top; }
.data-table tr:last-child td { border-bottom: 0; }
.data-table td:first-child { color: var(--ink); font-weight: 500; }
.data-table .math { font-family: var(--serif); font-size: 16px; }

.formula-list { margin: 0; padding: 0; list-style: none; }
.formula-list li {
  display: grid;
  grid-template-columns: 90px minmax(0, 1fr);
  gap: 12px;
  align-items: baseline;
  padding: 10px 0;
  border-top: 1px solid var(--line);
}
.formula-list li:first-child { border-top: 0; }
.formula-list .name { color: var(--muted); font-size: 12px; }
.formula-list .math { font-family: var(--serif); font-size: 17px; }

/* ---------- 刷题 ---------- */

.quiz-shell { max-width: 830px; margin: 0 auto; }

.quiz-intro {
  position: relative;
  padding: 30px 32px;
  background: var(--card);
  border: 1px solid var(--line);
  box-shadow: var(--shadow);
}
.quiz-intro h1 { margin: 14px 0 12px; font-size: clamp(32px, 4vw, 46px); line-height: 1.2; }
.quiz-intro .lead { max-width: 620px; font-size: 15px; }
.quiz-facts { display: grid; grid-template-columns: repeat(3, 1fr); gap: 1px; margin: 24px 0; background: var(--line); border: 1px solid var(--line); }
.quiz-facts div { padding: 14px 16px; background: var(--card); }
.quiz-facts b { display: block; font-family: var(--serif); font-size: 24px; }
.quiz-facts small { color: var(--muted); font-family: var(--mono); font-size: 9px; letter-spacing: 0.1em; }

.quiz-setup-row { display: flex; flex-wrap: wrap; align-items: center; gap: 12px; }
.switch {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  color: var(--muted);
  font-size: 12px;
  cursor: pointer;
}
.switch input { position: absolute; opacity: 0; pointer-events: none; }
.switch .track {
  position: relative;
  width: 34px;
  height: 18px;
  background: var(--line-strong);
  border-radius: 999px;
  transition: background 0.2s;
}
.switch .track::after {
  content: "";
  position: absolute;
  top: 2px;
  left: 2px;
  width: 14px;
  height: 14px;
  background: var(--card);
  border-radius: 50%;
  transition: transform 0.2s;
}
.switch input:checked + .track { background: var(--teal); }
.switch input:checked + .track::after { transform: translateX(16px); }

.quiz-stage { padding-top: 4px; }
.quiz-head {
  display: flex;
  align-items: center;
  gap: 16px;
  margin-bottom: 16px;
}
.quiz-head .qcount { font-family: var(--mono); font-size: 11px; letter-spacing: 0.08em; }
.quiz-head .qcount b { color: var(--accent); font-size: 15px; }
.quiz-head .timer { margin-left: auto; color: var(--muted); font-family: var(--mono); font-size: 11px; font-variant-numeric: tabular-nums; }
.quiz-head .timer.over { color: var(--accent); }

.qbar { height: 3px; margin-bottom: 22px; overflow: hidden; background: var(--line); }
.qbar i { display: block; height: 100%; background: var(--ink); transition: width 0.35s; }

.q-card {
  padding: 30px 32px;
  background: var(--card);
  border: 1px solid var(--line);
  box-shadow: var(--shadow);
}
.q-meta { display: flex; flex-wrap: wrap; align-items: center; gap: 8px; margin-bottom: 16px; }
.q-type { color: var(--accent); font-family: var(--mono); font-size: 9px; letter-spacing: 0.14em; }
.q-stem {
  margin: 0;
  font-family: var(--serif);
  font-size: 21px;
  font-weight: 600;
  line-height: 1.85;
}
.q-hint { margin-top: 14px; color: var(--muted); font-size: 12px; }

.opts { display: flex; flex-direction: column; gap: 9px; margin-top: 22px; }
.opt {
  display: flex;
  align-items: flex-start;
  gap: 14px;
  width: 100%;
  padding: 13px 16px;
  text-align: left;
  background: transparent;
  border: 1px solid var(--line);
  border-radius: 2px;
  transition: border-color 0.16s, background 0.16s, transform 0.16s;
}
.opt:hover:not(:disabled) { border-color: var(--line-strong); background: rgba(27, 33, 30, 0.025); }
.opt .letter {
  display: grid;
  width: 24px;
  height: 24px;
  flex: 0 0 24px;
  place-items: center;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 11px;
  border: 1px solid var(--line);
  border-radius: 50%;
}
.opt .txt { font-size: 14.5px; line-height: 1.7; padding-top: 1px; }
.opt.sel { border-color: var(--ink); background: rgba(27, 33, 30, 0.04); }
.opt.sel .letter { color: var(--card); background: var(--ink); border-color: var(--ink); }
.opt.correct { border-color: var(--teal); background: rgba(46, 107, 94, 0.07); }
.opt.correct .letter { color: #fff; background: var(--teal); border-color: var(--teal); }
.opt.wrong { border-color: var(--accent); background: rgba(196, 69, 44, 0.06); }
.opt.wrong .letter { color: #fff; background: var(--accent); border-color: var(--accent); }
.opt:disabled { cursor: default; }

.answer-area { margin-top: 22px; }
.answer-line {
  display: flex;
  align-items: baseline;
  gap: 12px;
  padding: 10px 0;
  border-bottom: 1px solid var(--line-strong);
}
.answer-line input {
  width: 100%;
  padding: 4px 0;
  font-family: var(--mono);
  font-size: 28px;
  font-variant-numeric: tabular-nums;
  letter-spacing: 0.02em;
  background: transparent;
  border: 0;
  outline: 0;
}
.answer-line input::placeholder { color: var(--faint); font-size: 16px; letter-spacing: 0; }
.answer-line .unit { flex: 0 0 auto; color: var(--muted); font-family: var(--mono); font-size: 13px; }
.answer-actions { display: flex; align-items: center; gap: 12px; margin-top: 18px; }
.answer-actions .target-note { color: var(--faint); font-family: var(--mono); font-size: 10px; }

.feedback {
  margin-top: 20px;
  padding: 18px 20px;
  background: rgba(27, 33, 30, 0.028);
  border-left: 2px solid var(--line-strong);
  animation: fadeUp 0.3s ease both;
}
.feedback.good { border-left-color: var(--teal); background: rgba(46, 107, 94, 0.05); }
.feedback.bad { border-left-color: var(--accent); background: rgba(196, 69, 44, 0.045); }
.feedback .verdict {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 10px;
  margin-bottom: 8px;
  font-family: var(--serif);
  font-size: 18px;
  font-weight: 700;
}
.feedback.good .verdict { color: var(--teal); }
.feedback.bad .verdict { color: var(--accent-2); }
.feedback .verdict small { color: var(--muted); font-family: var(--mono); font-size: 9.5px; font-weight: 400; letter-spacing: 0.04em; }
.feedback .answer-text { margin: 6px 0 8px; color: var(--ink); font-size: 13px; }
.feedback .ana { margin: 0; color: var(--ink-2); font-size: 13.5px; line-height: 1.85; }
.feedback .ana .math { font-family: var(--serif); font-size: 15px; }
.feedback .next-row { display: flex; justify-content: flex-end; margin-top: 14px; }

.quiz-done { padding: 34px; background: var(--card); border: 1px solid var(--line); box-shadow: var(--shadow); text-align: center; }
.score-ring { position: relative; width: 150px; height: 150px; margin: 6px auto 18px; }
.score-ring svg { width: 100%; height: 100%; transform: rotate(-90deg); }
.score-ring .track { fill: none; stroke: var(--line); stroke-width: 5; }
.score-ring .bar { fill: none; stroke: var(--accent); stroke-width: 5; stroke-linecap: round; }
.score-ring .inner { position: absolute; inset: 0; display: grid; place-content: center; }
.score-ring b { font-family: var(--serif); font-size: 42px; line-height: 1; }
.score-ring small { margin-top: 4px; color: var(--muted); font-family: var(--mono); font-size: 9px; letter-spacing: 0.12em; }
.quiz-done h2 { font-size: 28px; }
.quiz-done .sub { color: var(--muted); font-size: 13px; }
.result-stats { display: grid; grid-template-columns: repeat(3, 1fr); gap: 1px; margin: 24px 0; background: var(--line); border: 1px solid var(--line); }
.result-stats div { padding: 14px; background: var(--card); }
.result-stats b { display: block; font-family: var(--serif); font-size: 24px; }
.result-stats small { color: var(--muted); font-family: var(--mono); font-size: 9px; letter-spacing: 0.1em; }

.section-bars { margin: 0 0 24px; text-align: left; }
.section-bars .row { display: grid; grid-template-columns: 90px minmax(0, 1fr) 44px; gap: 12px; align-items: center; padding: 7px 0; font-size: 11px; }
.section-bars .row .t { color: var(--muted); }
.section-bars .track { height: 4px; overflow: hidden; background: var(--line); }
.section-bars .track i { display: block; height: 100%; background: var(--teal); }
.section-bars .row b { text-align: right; font-family: var(--mono); font-size: 10px; }

.wrong-list { margin: 0 0 24px; padding: 0; list-style: none; text-align: left; }
.wrong-list li { display: flex; gap: 10px; padding: 9px 0; font-size: 12px; line-height: 1.7; border-top: 1px solid var(--line); }
.wrong-list li .x { flex: 0 0 auto; color: var(--accent); font-family: var(--mono); font-size: 10px; }
.wrong-list li a { color: var(--muted); }
.wrong-list li a:hover { color: var(--accent); }

.quiz-done .actions { display: flex; flex-wrap: wrap; justify-content: center; gap: 10px; }

/* ---------- 全量内容入口 ---------- */

.feature-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 12px; margin-top: 16px; }
.feature-card {
  position: relative;
  display: flex;
  min-height: 180px;
  flex-direction: column;
  padding: 20px 18px 16px;
  background: var(--card);
  border: 1px solid var(--line);
  transition: border-color 0.2s, transform 0.2s;
}
.feature-card:hover { border-color: var(--line-strong); transform: translateY(-2px); }
.feature-no { color: var(--accent); font-family: var(--mono); font-size: 9px; letter-spacing: 0.12em; }
.feature-card h3 { margin: 8px 0 6px; font-size: 20px; }
.feature-card p { margin: 0 0 14px; color: var(--muted); font-size: 12px; line-height: 1.75; }
.feature-card b { margin-top: auto; color: var(--teal); font-size: 11px; font-weight: 500; }

/* ---------- 完整讲义 ---------- */

.lecture-tabs {
  position: sticky;
  top: 62px;
  z-index: 20;
  display: flex;
  gap: 6px;
  margin: 0 0 10px;
  padding: 12px 0;
  overflow-x: auto;
  background: rgba(245, 241, 231, 0.94);
  border-bottom: 1px solid var(--line);
  backdrop-filter: blur(10px);
}
.lecture-tabs a {
  flex: 0 0 auto;
  padding: 5px 10px;
  color: var(--muted);
  font-size: 11px;
  white-space: nowrap;
  border: 1px solid var(--line);
  border-radius: 999px;
}
.lecture-tabs a:hover { color: var(--accent); border-color: var(--accent); }
.lecture-tabs a.active { color: var(--card); background: var(--ink); border-color: var(--ink); }

.lecture-sec { margin-top: 38px; scroll-margin-top: 130px; }
.lecture-sec-head {
  padding: 8px 0 18px;
  border-bottom: 1px solid var(--line-strong);
}
.lecture-sec-head h2 {
  margin: 8px 0 10px;
  font-size: clamp(28px, 3.4vw, 42px);
  line-height: 1.25;
}
.lecture-sec-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 16px;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.04em;
}
.lecture-sec-meta a { color: var(--accent); border-bottom: 1px solid rgba(196, 69, 44, 0.35); }

.section-deep-link {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px 16px;
  margin: 18px 0 0;
  padding: 10px 14px;
  color: var(--muted);
  font-size: 11.5px;
  background: rgba(46, 107, 94, 0.045);
  border: 1px dashed rgba(46, 107, 94, 0.3);
}
.section-deep-link a { color: var(--teal); border-bottom: 1px solid rgba(46, 107, 94, 0.3); }
.section-deep-link a:last-child { margin-left: auto; }

.topic {
  position: relative;
  margin: 24px 0;
  padding: 24px 26px 20px;
  background: var(--card);
  border: 1px solid var(--line);
  border-left: 2px solid rgba(196, 69, 44, 0.55);
  scroll-margin-top: 130px;
}
.topic-head {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 20px;
  padding-bottom: 12px;
  border-bottom: 1px solid var(--line);
}
.topic-kp {
  display: inline-block;
  color: var(--accent);
  font-family: var(--mono);
  font-size: 9px;
  letter-spacing: 0.08em;
}
.topic-head h3 { margin-top: 5px; font-size: 22px; line-height: 1.45; }
.topic-meta { flex: 0 0 auto; color: var(--faint); font-family: var(--mono); font-size: 9.5px; }
.topic-link { margin: 10px 0 4px; color: var(--muted); font-size: 12px; }
.topic-link a { color: var(--teal); border-bottom: 1px solid rgba(46, 107, 94, 0.3); }

.topic-points {
  margin: 8px 0 0;
  padding: 0;
  list-style: none;
  counter-reset: tp;
}
.topic-points li {
  position: relative;
  padding: 9px 0 9px 30px;
  color: var(--ink-2);
  font-size: 14.5px;
  line-height: 1.85;
  border-top: 1px solid var(--line);
  counter-increment: tp;
}
.topic-points li:first-child { border-top: 0; }
.topic-points li::before {
  content: counter(tp, decimal-leading-zero);
  position: absolute;
  top: 12px;
  left: 0;
  color: var(--accent);
  font-family: var(--mono);
  font-size: 9px;
}

.tip-box {
  margin: 16px 0 0;
  padding: 14px 18px 10px;
  background: rgba(176, 135, 52, 0.065);
  border-left: 2px solid var(--gold);
}
.tip-box h4 {
  margin-bottom: 4px;
  color: var(--gold);
  font-family: var(--mono);
  font-size: 9px;
  font-weight: 600;
  letter-spacing: 0.14em;
}
.tip-box ul { margin: 0; padding: 0; list-style: none; }
.tip-box li {
  position: relative;
  padding: 5px 0 5px 15px;
  color: var(--ink-2);
  font-size: 13px;
  line-height: 1.8;
}
.tip-box li::before { content: "—"; position: absolute; left: 0; color: var(--gold); }

.topic-examples { margin-top: 18px; padding-top: 14px; border-top: 1px dashed var(--line-strong); }
.topic-examples-head {
  display: flex;
  justify-content: space-between;
  margin-bottom: 10px;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.08em;
}
.topic-examples-head span { color: var(--faint); }

.full-example summary { padding: 10px 14px; }
.full-example .ex-type {
  flex: 0 0 auto;
  padding: 1px 6px;
  color: var(--accent-2);
  font-family: var(--mono);
  font-size: 8.5px;
  background: var(--accent-soft);
}
.full-example .ex-title { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.full-example .ex-src { margin-left: auto; color: var(--faint); font-family: var(--mono); font-size: 9px; }
.full-example .example-body { padding: 4px 18px 18px; }
.ex-stem {
  margin: 4px 0 10px;
  color: var(--ink);
  font-family: var(--serif);
  font-size: 16px;
  line-height: 1.8;
}
.ex-opts { margin: 8px 0 10px; padding: 0; list-style: none; display: grid; gap: 5px; }
.ex-opts li {
  display: flex;
  align-items: baseline;
  gap: 10px;
  padding: 5px 10px;
  color: var(--ink-2);
  font-size: 13.5px;
  line-height: 1.7;
  background: rgba(27, 33, 30, 0.025);
  border: 1px solid var(--line);
}
.opt-letter {
  display: inline-grid;
  width: 18px;
  height: 18px;
  flex: 0 0 18px;
  place-items: center;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 9px;
  border: 1px solid var(--line);
  border-radius: 50%;
}
.ex-answer {
  display: flex;
  align-items: baseline;
  gap: 10px;
  margin: 10px 0;
  padding: 8px 12px;
  background: var(--teal-soft);
  border-left: 2px solid var(--teal);
}
.ex-answer > span {
  flex: 0 0 auto;
  color: var(--teal);
  font-family: var(--mono);
  font-size: 9px;
  letter-spacing: 0.08em;
}
.ex-answer > div { color: var(--ink); font-size: 13.5px; line-height: 1.8; }
.ex-steps { margin: 8px 0 0; padding: 0 0 0 22px; }
.ex-steps li { padding: 4px 0; color: var(--ink-2); font-size: 13px; line-height: 1.8; }
.ex-note { margin: 8px 0 0; color: var(--faint); font-size: 11px; line-height: 1.7; }
.lecture-foot { display: flex; flex-wrap: wrap; gap: 10px; justify-content: flex-end; margin: 30px 0 0; }

/* ---------- 例题库 ---------- */

.example-grid { display: grid; gap: 14px; margin-top: 18px; }
.example-wrap {
  padding: 10px 12px;
  background: var(--card);
  border: 1px solid var(--line);
}
.example-wrap-meta {
  margin-bottom: 6px;
  color: var(--faint);
  font-family: var(--mono);
  font-size: 9px;
  letter-spacing: 0.08em;
}
.example-wrap .full-example { border: 0; background: transparent; margin: 0; }
.example-wrap .full-example summary { padding: 6px 2px 10px; }
.example-wrap .full-example .example-body { padding: 0 2px 8px; }
.example-wrap .full-example summary::before { content: "例"; }

/* ---------- 逐帧索引 ---------- */

.frame-jump {
  padding: 5px 10px;
  color: var(--muted);
  font-size: 11px;
  border: 1px solid var(--line);
  border-radius: 999px;
}
.frame-jump:hover { color: var(--accent); border-color: var(--accent); }
.frames-sec { margin-top: 30px; scroll-margin-top: 90px; }
.frames-head {
  display: flex;
  align-items: baseline;
  gap: 12px;
  padding: 8px 0 12px;
  border-bottom: 1px solid var(--line-strong);
}
.frames-head span { color: var(--accent); font-family: var(--mono); font-size: 9px; letter-spacing: 0.08em; }
.frames-head h2 { font-size: 22px; }
.frames-head small { margin-left: auto; color: var(--faint); font-family: var(--mono); font-size: 9px; }
.frame-row {
  display: grid;
  grid-template-columns: 64px 70px 54px minmax(0, 1fr);
  gap: 12px;
  align-items: start;
  padding: 11px 0;
  border-bottom: 1px solid var(--line);
}
.frame-p { color: var(--accent); font-family: var(--mono); font-size: 10.5px; }
.frame-time { color: var(--muted); font-family: var(--mono); font-size: 10.5px; }
.frame-type {
  display: inline-block;
  width: fit-content;
  padding: 1px 5px;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 8.5px;
  border: 1px solid var(--line);
}
.frame-type.t-example, .frame-type.t-exercise { color: var(--accent-2); border-color: rgba(196, 69, 44, 0.35); }
.frame-type.t-tip { color: var(--gold); border-color: rgba(176, 135, 52, 0.4); }
.frame-main b { display: block; color: var(--ink); font-size: 13px; font-weight: 500; line-height: 1.6; }
.frame-main p { margin: 2px 0 0; color: var(--muted); font-size: 11.5px; line-height: 1.75; }

/* ---------- 题库 ---------- */

.bank-panel { margin-top: 18px; }
.bank-filters {
  display: grid;
  grid-template-columns: 1.2fr 1.5fr 0.8fr 1.4fr;
  gap: 10px;
  padding: 14px 16px;
  background: var(--card);
  border: 1px solid var(--line);
}
.bank-filters label { display: flex; flex-direction: column; gap: 4px; color: var(--faint); font-family: var(--mono); font-size: 9px; letter-spacing: 0.08em; }
.bank-filters select, .bank-filters input, .bank-tools select {
  width: 100%;
  min-height: 32px;
  padding: 0 8px;
  color: var(--ink);
  font-family: var(--sans);
  font-size: 12px;
  background: var(--paper);
  border: 1px solid var(--line-strong);
  border-radius: 2px;
}
.bank-tools {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 10px;
  padding: 12px 2px;
  color: var(--muted);
  font-size: 11px;
}
.bank-tools b { color: var(--accent); font-family: var(--mono); }
.bank-tools label { display: inline-flex; align-items: center; gap: 6px; font-size: 10px; }
.bank-tools select { width: auto; min-height: 28px; }
.bank-tools .btn { margin-left: 0; }
.bank-list { display: grid; gap: 10px; }
.bank-item {
  padding: 16px 18px;
  background: var(--card);
  border: 1px solid var(--line);
}
.bank-item-head { display: flex; flex-wrap: wrap; align-items: center; gap: 8px; }
.bank-id { color: var(--faint); font-size: 9px; }
.bank-diff { color: var(--muted); font-family: var(--mono); font-size: 9px; }
.bank-target { color: var(--accent); font-family: var(--mono); font-size: 9px; }
.bank-stem { margin: 10px 0 8px; color: var(--ink); font-family: var(--serif); font-size: 16px; line-height: 1.8; }
.bank-opts { margin: 6px 0; }
.bank-reveal {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 0;
  color: var(--teal);
  font-size: 11px;
  background: none;
  border: 0;
  border-bottom: 1px solid rgba(46, 107, 94, 0.3);
}
.bank-reveal span { font-family: var(--mono); }
.bank-detail { margin-top: 8px; padding-top: 6px; border-top: 1px dashed var(--line); }
.bank-ana { margin: 8px 0; color: var(--ink-2); font-size: 12.5px; line-height: 1.8; }
.bank-goto { color: var(--muted); font-size: 11px; border-bottom: 1px solid var(--line); }
.bank-goto:hover { color: var(--accent); }
.bank-pager { display: flex; flex-wrap: wrap; align-items: center; gap: 5px; justify-content: center; margin-top: 18px; }
.bank-pager button {
  min-width: 28px;
  padding: 4px 7px;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 10px;
  background: transparent;
  border: 1px solid var(--line);
}
.bank-pager button.active { color: var(--card); background: var(--ink); border-color: var(--ink); }
.bank-pager button:hover { border-color: var(--line-strong); }

/* ---------- 九讲总览 / 搜索 ---------- */

.lecture-row h3 { font-size: 19px; }
.lecture-row .sub { gap: 12px; }
.quick-search { display: flex; gap: 8px; margin-top: 12px; }
.quick-search input {
  min-width: 0;
  flex: 1;
  padding: 8px 10px;
  color: var(--ink);
  font-size: 12px;
  background: var(--paper);
  border: 1px solid var(--line-strong);
}
.big-search { display: flex; gap: 10px; max-width: 680px; margin-top: 22px; }
.big-search input {
  min-width: 0;
  flex: 1;
  padding: 12px 14px;
  color: var(--ink);
  font-family: var(--serif);
  font-size: 19px;
  background: var(--card);
  border: 1px solid var(--line-strong);
  outline: 0;
}
.big-search input:focus { border-color: var(--ink); }
.search-count { margin: 18px 0 8px; color: var(--muted); font-family: var(--mono); font-size: 10px; letter-spacing: 0.08em; }
.search-count b { color: var(--accent); }
.search-hit {
  display: block;
  margin: 10px 0;
  padding: 16px 18px;
  background: var(--card);
  border: 1px solid var(--line);
  transition: border-color 0.2s, transform 0.2s;
}
.search-hit:hover { border-color: var(--line-strong); transform: translateX(3px); }
.search-meta { color: var(--faint); font-family: var(--mono); font-size: 9px; letter-spacing: 0.06em; }
.search-hit h3 { margin: 6px 0 4px; font-size: 18px; }
.search-hit p { margin: 0; color: var(--muted); font-size: 12.5px; line-height: 1.75; display: -webkit-box; -webkit-line-clamp: 2; -webkit-box-orient: vertical; overflow: hidden; }

/* ---------- 页脚 / 提示 ---------- */

.site-foot {
  padding: 24px 0 30px;
  color: var(--faint);
  font-size: 10.5px;
  line-height: 1.8;
  border-top: 1px solid var(--line);
}
.site-foot a { color: var(--muted); border-bottom: 1px solid var(--line); }
.site-foot a:hover { color: var(--accent); }

.toast {
  position: fixed;
  bottom: 28px;
  left: 50%;
  z-index: 100;
  padding: 10px 18px;
  color: var(--card);
  font-size: 12px;
  background: var(--ink);
  border-radius: 2px;
  box-shadow: 0 12px 30px -12px rgba(0, 0, 0, 0.5);
  opacity: 0;
  transform: translate(-50%, 12px);
  pointer-events: none;
  transition: opacity 0.25s, transform 0.25s;
}
.toast.show { opacity: 1; transform: translate(-50%, 0); }

/* ---------- 公式排版 ---------- */

.math { white-space: nowrap; font-variant-numeric: tabular-nums; }
.mfrac {
  display: inline-flex;
  flex-direction: column;
  margin: 0 0.14em;
  vertical-align: 0.3em;
  text-align: center;
  font-size: 0.94em;
  line-height: 1.12;
}
.mnum { padding: 0 0.22em 0.1em; border-bottom: 1px solid currentColor; }
.mden { padding: 0.08em 0.22em 0; }
.mtext { font-style: normal; }
.mbar { position: relative; display: inline-block; padding-top: 0.12em; }
.mbar::after {
  content: "";
  position: absolute;
  top: 0.02em;
  right: 0;
  left: 0;
  height: 1px;
  background: currentColor;
}
.msqrt { white-space: nowrap; }
.mrad { border-top: 1px solid currentColor; padding: 0 0.08em; }
sup, sub { font-size: 0.66em; line-height: 0; }

/* ---------- 动效 ---------- */

@keyframes fadeUp {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: none; }
}

@keyframes rise {
  from { opacity: 0; transform: translateY(10px); }
  to { opacity: 1; transform: none; }
}

.view > * { animation: rise 0.45s cubic-bezier(0.22, 1, 0.36, 1) both; }
.view > *:nth-child(2) { animation-delay: 0.04s; }
.view > *:nth-child(3) { animation-delay: 0.08s; }
.view > *:nth-child(4) { animation-delay: 0.12s; }

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation: none !important; transition: none !important; scroll-behavior: auto !important; }
  .kp { opacity: 1; transform: none; }
}

/* ---------- 响应式 ---------- */

@media (max-width: 1180px) {
  .sidebar { width: 252px; }
  .main { margin-left: 252px; }
  .view { width: min(100% - 56px, 960px); }
  .topbar { padding: 0 28px; }
  .hero { grid-template-columns: minmax(0, 1.4fr) minmax(230px, 0.6fr); gap: 30px; }
  .hero-num { font-size: 170px; }
}

@media (max-width: 980px) {
  .sidebar { transform: translateX(-100%); width: 282px; box-shadow: 20px 0 50px rgba(0, 0, 0, 0.3); }
  .sidebar.open { transform: none; }
  .sidebar-close { display: block; }
  body.nav-open { overflow: hidden; }
  .main { margin-left: 0; }
  .menu-btn { display: block; }
  .topbar { padding: 0 20px; }
  .view { width: min(100% - 40px, 780px); padding-top: 30px; }
  .hero { grid-template-columns: 1fr; gap: 28px; padding-top: 6px; }
  .hero-side { min-height: 0; display: grid; grid-template-columns: 1.2fr 0.8fr; align-items: stretch; }
  .hero-num { display: none; }
  .hero h1 { font-size: clamp(44px, 9vw, 66px); }
  .split { grid-template-columns: 1fr; gap: 26px; }
  .takeaways { grid-template-columns: 1fr; }
  .takeaway { min-height: 0; padding: 16px 18px; }
  .cheat-grid { grid-template-columns: 1fr; }
  .cheat-card.wide { grid-column: auto; }
  .bank-filters { grid-template-columns: 1fr 1fr; }
  .topic { padding: 20px 20px 16px; }
  .feature-grid { grid-template-columns: 1fr; }
  .feature-card { min-height: 0; }
}

@media (max-width: 720px) {
  .lecture-tabs { top: 56px; }
  .lecture-sec { margin-top: 28px; scroll-margin-top: 110px; }
  .lecture-sec-head h2 { font-size: 27px; }
  .topic { padding: 17px 14px 12px; margin: 16px 0; }
  .topic-head { flex-direction: column; gap: 4px; }
  .topic-head h3 { font-size: 19px; }
  .topic-points li { font-size: 13.5px; padding-left: 24px; }
  .topic-points li::before { font-size: 8px; }
  .frame-row { grid-template-columns: 48px 50px 42px minmax(0, 1fr); gap: 7px; }
  .frame-main b { font-size: 12px; }
  .frame-main p { font-size: 10.5px; }
  .bank-filters { grid-template-columns: 1fr; }
  .bank-tools .btn { flex: 1 1 auto; }
  .bank-item { padding: 13px 12px; }
  .bank-stem { font-size: 15px; }
  .frames-head small { display: none; }
}

@media (max-width: 720px) {
  body { font-size: 15px; }
  .topbar { min-height: 56px; gap: 10px; }
  .crumb { font-size: 9px; }
  .top-actions .btn { min-height: 34px; padding: 0 12px; font-size: 11px; }
  .view { width: calc(100% - 28px); padding-bottom: 64px; }
  .hero { padding-bottom: 28px; }
  .hero h1 { margin: 16px 0 16px; }
  .hero-lead { font-size: 15px; }
  .hero-side { grid-template-columns: 1fr; }
  .chapter-chip { display: none; }
  .hero-meta { gap: 6px; }
  .hero-meta .chip { padding: 3px 8px; font-size: 9.5px; }
  .hero-actions { display: grid; grid-template-columns: 1fr 1fr; }
  .hero-actions .btn { width: 100%; }
  .quote-card p { font-size: 18px; }
  .stats { grid-template-columns: 1fr 1fr; }
  .stat { padding: 16px 12px 16px 0; border-bottom: 1px solid var(--line); }
  .stat + .stat { padding-left: 16px; }
  .stat:nth-child(2) { border-right: 0; }
  .stat:nth-child(3), .stat:nth-child(4) { border-bottom: 0; }
  .stat b { font-size: 24px; }
  .path-row { grid-template-columns: 38px minmax(0, 1fr) auto; gap: 12px; padding: 16px 0; }
  .path-row .no { font-size: 21px; }
  .path-row h3 { font-size: 17px; }
  .section-title { margin-top: 38px; }
  .section-title h2 { font-size: 22px; }
  .section-hero .section-no { display: none; }
  .section-hero h1 { font-size: 29px; line-height: 1.28; }
  .kp { padding: 22px 18px 18px; margin: 16px 0; }
  .kp-head { padding-right: 0; gap: 10px; }
  .kp-index { width: 30px; flex-basis: 30px; font-size: 21px; }
  .kp h3 { font-size: 20px; }
  .master-btn { position: static; margin: 12px 0 0 40px; }
  .kp-gist { font-size: 16px; padding: 12px 14px; }
  .kp-points li { font-size: 14px; }
  .formula-box { padding: 13px 14px; }
  .formula-box .math { font-size: 16px; }
  .example .example-body { padding-left: 18px; }
  .kp-foot a { margin-left: 0; }
  .pager { flex-direction: column; }
  .pager a.next { margin-left: 0; text-align: left; }
  .quiz-intro, .q-card { padding: 22px 18px; }
  .quiz-facts, .quiz-facts { grid-template-columns: 1fr; }
  .result-stats { grid-template-columns: 1fr; }
  .q-stem { font-size: 18px; }
  .opt .txt { font-size: 13.5px; }
  .answer-line input { font-size: 24px; }
  .quiz-done { padding: 24px 18px; }
  .fraction-grid { grid-template-columns: repeat(4, 1fr); }
  .decision-list li { grid-template-columns: 1fr; gap: 2px; }
  .formula-list li { grid-template-columns: 1fr; gap: 2px; }
  .data-table { font-size: 12px; }
  .data-table th, .data-table td { padding: 7px 6px; }
}

/* ---------- 长公式 / 长选项防溢出 ---------- */

.view, .main, .page-hero, .topic, .example, .example-body, .example-wrap, .example-grid, .search-hit { min-width: 0; }
.example-grid { grid-template-columns: minmax(0, 1fr); }
.example-wrap-meta { overflow-wrap: anywhere; }
.example-wrap .ex-title { min-width: 0; }
.topic-points li, .tip-box li, .ex-stem, .ex-opts li, .ex-answer, .ex-steps li, .search-hit p {
  overflow-wrap: anywhere;
  word-break: break-word;
}
.example summary { flex-wrap: wrap; }
.ex-title { white-space: normal; overflow-wrap: anywhere; }
.ex-opts li { white-space: normal; }

@media (max-width: 620px) {
  .view { overflow-x: hidden; }
  .example summary { gap: 6px; }
  .ex-title { flex: 1 1 100%; order: 3; }
  .ex-src { margin-left: auto; }
  .ex-opts { padding-left: 0; }
  .ex-opts li { display: flex; gap: 8px; align-items: flex-start; }
  .ex-opts .opt-letter { flex: 0 0 auto; }
  .topic-head { flex-wrap: wrap; gap: 8px; }
  .topic-meta { margin-left: 0; }
}

/* ---------- 打印 ---------- */

@media print {
  .sidebar, .topbar, .pager, .master-btn, .site-foot, .scrim, .toast, .quiz-shell { display: none !important; }
  .main { margin: 0; }
  .view { width: 100%; padding: 0; }
  body { background: #fff; font-size: 11pt; }
  .kp, .takeaway, .cheat-card { box-shadow: none; break-inside: avoid; }
  .kp { opacity: 1; transform: none; }
}

.ex-computed { color: #7a5a1e; border-color: #d8c58f; background: #f7f0dc; }