/* Claude 认证中文书系 — 三主题系统
   Theme B（默认）日本書籍 · Theme A 技术文档 · Theme C 夜间暗色 */

@import url('https://fonts.googleapis.com/css2?family=Noto+Serif+SC:wght@300;400;500;700;900&family=Noto+Sans+SC:wght@100;300;400;500;700;900&family=JetBrains+Mono:wght@400;500&display=swap');

:root {
  /* 配色：米白 + 墨黑 + 一个砖红 */
  --color-bg: #faf8f3;
  --color-surface: #ffffff;
  --color-ink: #1a1a1a;
  --color-ink-soft: #3a3a3a;
  --color-ink-mute: #8a8a85;
  --color-rule: #d8d4cb;
  --color-rule-soft: #ebe7de;
  --color-accent: #8b3a3a;       /* 砖红 */
  --color-accent-ink: #5c2525;

  /* 双轨用边框区分，不再用色块 */
  --color-basic: #2d5a3d;        /* 墨绿（低饱和）*/
  --color-advanced: #2a4858;     /* 墨蓝（低饱和）*/
  --color-exam: #8b3a3a;         /* 考点用主强调色 */

  /* 字体：宋体正文 + 黑体标题 */
  --font-serif: 'Noto Serif SC', 'Songti SC', 'STSong', serif;
  --font-sans: 'Noto Sans SC', -apple-system, system-ui, sans-serif;
  --font-mono: 'JetBrains Mono', 'Courier New', monospace;
}

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html { background: var(--color-bg); }

body {
  font-family: var(--font-serif);
  background: var(--color-bg);
  color: var(--color-ink);
  line-height: 1.95;
  font-size: 18.5px;
  font-weight: 400;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  font-feature-settings: "palt" 1;
}

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

/* ── 布局 ── 更窄更克制 */
.page-wrapper {
  max-width: 720px;
  margin: 0 auto;
  padding: 3rem 1.75rem 6rem;
}

/* ── 顶部导航 ── 极细 */
.nav-bar {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  padding-bottom: 1rem;
  border-bottom: 1px solid var(--color-rule);
  margin-bottom: 5rem;
  font-family: var(--font-sans);
  font-size: 0.75rem;
  font-weight: 300;
  letter-spacing: 0.1em;
  color: var(--color-ink-mute);
  text-transform: uppercase;
}
.nav-bar a {
  color: var(--color-ink);
  text-decoration: none;
  transition: color 0.2s;
}
.nav-bar a:hover { color: var(--color-accent); }
.nav-bar span { color: var(--color-ink-mute); }

/* ── 课程标题区 ── 极细/极粗对比 */
.lesson-header {
  margin-bottom: 5rem;
  padding-bottom: 3rem;
  border-bottom: 1px solid var(--color-rule);
}
.vol-tag {
  display: inline-block;
  font-family: var(--font-sans);
  font-size: 0.68rem;
  font-weight: 300;
  letter-spacing: 0.25em;
  color: var(--color-ink-mute);
  text-transform: uppercase;
  margin-bottom: 2rem;
  background: none;
  padding: 0;
  border-bottom: 1px solid var(--color-ink);
  padding-bottom: 0.3rem;
}
.lesson-header h1 {
  font-family: var(--font-sans);
  font-size: 3.25rem;
  font-weight: 900;
  color: var(--color-ink);
  line-height: 1.15;
  letter-spacing: -0.01em;
  margin-bottom: 1.5rem;
}
.lesson-intro {
  font-family: var(--font-serif);
  font-size: 1.2rem;
  font-weight: 300;
  line-height: 1.75;
  color: var(--color-ink-soft);
  border: none;
  padding: 0;
  max-width: 42em;
  font-style: italic;
}

/* ── 正文排版 ── */
h2 {
  font-family: var(--font-sans);
  font-size: 1.65rem;
  font-weight: 900;
  color: var(--color-ink);
  letter-spacing: -0.005em;
  margin: 4rem 0 1.5rem;
  padding-top: 2rem;
  border-top: 1px solid var(--color-rule);
  position: relative;
}
h2::before {
  content: '';
  display: block;
  width: 32px;
  height: 2px;
  background: var(--color-ink);
  position: absolute;
  top: -1px;
  left: 0;
}

h3 {
  font-family: var(--font-sans);
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--color-ink);
  margin: 2.5rem 0 0.75rem;
  letter-spacing: 0.01em;
}

h4 {
  font-family: var(--font-sans);
  font-size: 0.9rem;
  font-weight: 700;
  color: var(--color-ink-soft);
  margin: 1.5rem 0 0.5rem;
  letter-spacing: 0.02em;
}

p {
  margin: 1rem 0;
  font-family: var(--font-serif);
  line-height: 1.95;
}

strong { font-weight: 700; color: var(--color-ink); }
em { font-style: italic; color: var(--color-ink-soft); }

a {
  color: var(--color-accent);
  text-decoration: none;
  border-bottom: 1px solid var(--color-accent);
  transition: all 0.2s;
}
a:hover { color: var(--color-accent-ink); border-bottom-color: var(--color-accent-ink); }

ul, ol { padding-left: 1.5rem; margin: 1rem 0; }
li { margin: 0.4rem 0; line-height: 1.85; }

/* ── 表格 ── 学术论文三线式 */
table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.75rem 0;
  font-family: var(--font-serif);
  font-size: 0.92rem;
  border-top: 2px solid var(--color-ink);
  border-bottom: 2px solid var(--color-ink);
}
table thead tr {
  border-bottom: 1px solid var(--color-ink);
}
table th {
  font-family: var(--font-sans);
  font-weight: 700;
  text-align: left;
  padding: 0.75rem 0.6rem;
  font-size: 0.82rem;
  letter-spacing: 0.02em;
  color: var(--color-ink);
}
table td {
  padding: 0.7rem 0.6rem;
  vertical-align: top;
  line-height: 1.65;
  border-bottom: 1px solid var(--color-rule-soft);
}
table tr:last-child td { border-bottom: none; }

/* ── 代码 ── */
code {
  font-family: var(--font-mono);
  background: transparent;
  color: var(--color-accent);
  padding: 0 0.15em;
  font-size: 0.88em;
  font-weight: 500;
}
pre {
  background: var(--color-ink);
  color: #e8e4da;
  padding: 1.5rem 1.75rem;
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: 0.82rem;
  line-height: 1.75;
  margin: 1.5rem 0;
  border-radius: 0;
  border-left: 2px solid var(--color-accent);
}
pre code { background: none; padding: 0; color: inherit; font-size: inherit; }

/* ── 引用 ── 日式竖线引文 */
blockquote {
  font-family: var(--font-serif);
  font-size: 1.2rem;
  font-weight: 300;
  font-style: italic;
  line-height: 1.7;
  color: var(--color-ink-soft);
  margin: 2rem 0;
  padding: 0.5rem 0 0.5rem 2rem;
  border-left: 1px solid var(--color-ink);
}

/* ── 双轨内容 ── 去色块，改用极细边框 + 标签 */
.track {
  border: none;
  background: none;
  padding: 1.5rem 0 1rem;
  margin: 2.5rem 0;
  position: relative;
  border-top: 1px solid var(--color-rule);
}

.track-label {
  font-family: var(--font-sans);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.25em;
  text-transform: uppercase;
  margin-bottom: 1.25rem;
  display: inline-block;
  padding-bottom: 0.25rem;
}

.track-basic { border-top-color: var(--color-basic); border-top-width: 2px; }
.track-basic .track-label {
  color: var(--color-basic);
  border-bottom: 1px solid var(--color-basic);
}

.track-advanced { border-top-color: var(--color-advanced); border-top-width: 2px; }
.track-advanced .track-label {
  color: var(--color-advanced);
  border-bottom: 1px solid var(--color-advanced);
}

/* ── 考点 ── 极简边框化 */
.exam-point {
  background: none;
  border: none;
  border-left: 2px solid var(--color-exam);
  padding: 0.5rem 0 0.5rem 1.25rem;
  margin: 1.5rem 0;
  font-family: var(--font-serif);
  font-size: 0.95rem;
  color: var(--color-ink);
}
.exam-point::before {
  content: '考点';
  display: block;
  font-family: var(--font-sans);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.25em;
  color: var(--color-exam);
  margin-bottom: 0.4rem;
  text-transform: uppercase;
}

/* ── 考点（callout 变体）── vol-11 / vol-14 使用，含显式 h2 */
.exam-callout {
  background: none;
  border: none;
  border-left: 2px solid var(--color-exam);
  padding: 0.5rem 0 0.5rem 1.25rem;
  margin: 1.5rem 0;
  font-family: var(--font-serif);
  font-size: 0.95rem;
  color: var(--color-ink);
}
.exam-callout h2 {
  font-family: var(--font-sans);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.25em;
  color: var(--color-exam);
  margin: 0 0 0.4rem;
  padding: 0;
  border: none;
  text-transform: uppercase;
}
.exam-callout h2::before { display: none; }
.exam-callout ul { margin: 0.5rem 0; }
.exam-callout p { margin: 0.6rem 0 0; font-size: 0.9rem; }

/* ══════════════════════════════════════
   教学组件 — 极简化改造
   ══════════════════════════════════════ */

/* ── 情景导入 ── 不再用深色渐变，改纸卡风 */
.scenario {
  background: #f3efe4;
  color: var(--color-ink);
  border: none;
  border-radius: 0;
  padding: 1.75rem 2rem;
  margin: 2rem 0;
  position: relative;
  overflow: hidden;
}
.scenario::before {
  content: none;
}
.scenario .scenario-label {
  font-family: var(--font-sans);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.25em;
  color: var(--color-accent);
  margin-bottom: 0.75rem;
  text-transform: uppercase;
}
.scenario p {
  margin: 0.6rem 0;
  font-size: 0.98rem;
  line-height: 1.8;
  color: var(--color-ink-soft);
}
.scenario strong { color: var(--color-ink); }

/* ── 好/坏对比 ── */
.compare-block {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.5rem;
  margin: 1.75rem 0;
}
@media (max-width: 640px) { .compare-block { grid-template-columns: 1fr; gap: 1rem; } }

.compare-bad, .compare-good {
  border: none;
  border-radius: 0;
  padding: 1.25rem 0 0;
  background: none;
  border-top: 2px solid var(--color-ink);
}
.compare-bad { border-top-color: #b94a4a; }
.compare-good { border-top-color: var(--color-basic); }

.compare-bad .compare-label,
.compare-good .compare-label {
  font-family: var(--font-sans);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.25em;
  margin-bottom: 0.75rem;
  text-transform: uppercase;
}
.compare-bad .compare-label { color: #b94a4a; }
.compare-good .compare-label { color: var(--color-basic); }

.compare-bad .prompt-text,
.compare-good .prompt-text {
  font-family: var(--font-mono);
  font-size: 0.82rem;
  line-height: 1.7;
  white-space: pre-wrap;
  background: #efebe0;
  padding: 0.9rem 1rem;
  border-radius: 0;
  margin: 0.6rem 0;
  color: var(--color-ink);
}

.compare-note {
  font-size: 0.85rem;
  color: var(--color-ink-mute);
  margin-top: 0.5rem;
  font-family: var(--font-serif);
  font-style: italic;
}

/* ── 关键洞见 ── 大号宋体 + 竖线 */
.insight {
  border: none;
  border-left: 1px solid var(--color-ink);
  background: none;
  padding: 0.75rem 0 0.75rem 1.75rem;
  border-radius: 0;
  margin: 2rem 0;
  font-family: var(--font-serif);
  font-size: 1.2rem;
  font-weight: 300;
  color: var(--color-ink);
  line-height: 1.7;
  font-style: italic;
}
.insight::before { content: none; }

/* ── 易错点 ── */
.mistake {
  background: none;
  border: none;
  border-left: 2px solid #b8860b;
  border-radius: 0;
  padding: 0.5rem 0 0.5rem 1.25rem;
  margin: 1.5rem 0;
  font-family: var(--font-serif);
  font-size: 0.95rem;
  color: var(--color-ink-soft);
}
.mistake .mistake-label {
  font-family: var(--font-sans);
  font-weight: 700;
  color: #8b6508;
  font-size: 0.68rem;
  letter-spacing: 0.25em;
  text-transform: uppercase;
  margin-bottom: 0.4rem;
}

/* ── 考题 ── */
.exam-quiz {
  background: none;
  border: none;
  border-top: 1px solid var(--color-rule);
  border-bottom: 1px solid var(--color-rule);
  border-radius: 0;
  padding: 1.5rem 0;
  margin: 2rem 0;
}
.exam-quiz .quiz-label {
  font-family: var(--font-sans);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.25em;
  color: var(--color-accent);
  text-transform: uppercase;
  margin-bottom: 1rem;
}
.exam-quiz .quiz-q {
  font-family: var(--font-serif);
  font-weight: 500;
  font-size: 1.05rem;
  color: var(--color-ink);
  margin-bottom: 1rem;
  line-height: 1.7;
}
.exam-quiz .quiz-options {
  list-style: none;
  padding: 0;
  margin: 0 0 1rem;
}
.exam-quiz .quiz-options li {
  padding: 0.5rem 0 0.5rem 1.75rem;
  border: none;
  background: none;
  border-radius: 0;
  font-family: var(--font-serif);
  font-size: 0.95rem;
  color: var(--color-ink-soft);
  position: relative;
  margin: 0.2rem 0;
}
.exam-quiz .quiz-options li::before {
  content: '○';
  position: absolute;
  left: 0;
  color: var(--color-ink-mute);
  font-size: 0.8rem;
  top: 0.65rem;
}
.exam-quiz .quiz-answer {
  display: none;
  background: none;
  border-left: 2px solid var(--color-basic);
  border-radius: 0;
  padding: 0.5rem 0 0.5rem 1rem;
  font-family: var(--font-serif);
  font-size: 0.95rem;
  color: var(--color-ink);
  margin-top: 0.75rem;
  line-height: 1.75;
}
.exam-quiz .quiz-answer.show { display: block; }

.quiz-toggle {
  font-family: var(--font-sans);
  background: none;
  color: var(--color-ink);
  border: 1px solid var(--color-ink);
  border-radius: 0;
  padding: 0.4rem 1.25rem;
  font-size: 0.72rem;
  letter-spacing: 0.18em;
  cursor: pointer;
  text-transform: uppercase;
  font-weight: 500;
  transition: all 0.2s;
}
.quiz-toggle:hover { background: var(--color-ink); color: var(--color-bg); }

/* 兼容 lesson-14 及之后的 .quiz-block onclick 样式 */
.quiz-block {
  border-top: 1px solid var(--color-rule);
  border-bottom: 1px solid var(--color-rule);
  padding: 1.5rem 0;
  margin: 2rem 0;
  cursor: pointer;
  transition: border-color 0.2s;
}
.quiz-block:hover { border-color: var(--color-ink); }
.quiz-block .quiz-q {
  font-family: var(--font-serif);
  font-weight: 500;
  font-size: 1.05rem;
  line-height: 1.7;
  color: var(--color-ink);
}
.quiz-block .quiz-q::before {
  content: 'Q.';
  font-family: var(--font-sans);
  font-weight: 900;
  color: var(--color-accent);
  margin-right: 0.5rem;
  letter-spacing: 0.05em;
}
.quiz-block .quiz-a {
  display: none;
  margin-top: 1rem;
  padding-top: 1rem;
  border-top: 1px solid var(--color-rule-soft);
  font-family: var(--font-serif);
  font-size: 0.95rem;
  line-height: 1.8;
  color: var(--color-ink-soft);
}
.quiz-block .quiz-a::before {
  content: 'A.';
  font-family: var(--font-sans);
  font-weight: 900;
  color: var(--color-basic);
  margin-right: 0.5rem;
  letter-spacing: 0.05em;
}
.quiz-block.open .quiz-a { display: block; }
.quiz-a .correct { color: #15803d; font-weight: 700; }

/* ── 速记卡片 ── 去深色，改纯黑边框 */
.cheatsheet {
  background: none;
  color: var(--color-ink);
  border: none;
  border-top: 2px solid var(--color-ink);
  border-bottom: 2px solid var(--color-ink);
  border-radius: 0;
  padding: 2rem 0;
  margin: 4rem 0 2rem;
}
.cheatsheet .cheat-label {
  font-family: var(--font-sans);
  font-size: 0.72rem;
  font-weight: 900;
  letter-spacing: 0.3em;
  color: var(--color-ink);
  text-transform: uppercase;
  margin-bottom: 1.5rem;
  display: block;
}
.cheatsheet h3 {
  font-family: var(--font-sans);
  color: var(--color-ink);
  font-size: 0.82rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  margin: 1.5rem 0 0.5rem;
  border-bottom: 1px solid var(--color-rule);
  padding-bottom: 0.35rem;
  text-transform: uppercase;
}
.cheatsheet ul { padding-left: 1.2rem; margin: 0; }
.cheatsheet li {
  font-family: var(--font-serif);
  font-size: 0.92rem;
  color: var(--color-ink-soft);
  margin: 0.4rem 0;
  line-height: 1.7;
}
.cheatsheet li strong { color: var(--color-ink); }
.cheatsheet .tag {
  display: inline-block;
  background: none;
  color: var(--color-accent);
  font-family: var(--font-sans);
  font-size: 0.66rem;
  padding: 0.05rem 0.35rem;
  border: 1px solid var(--color-accent);
  font-weight: 500;
  letter-spacing: 0.12em;
  margin-right: 0.4rem;
  vertical-align: middle;
  text-transform: uppercase;
}
.cheatsheet-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0 1.5rem;
  margin: 0.75rem 0;
}
@media (max-width: 640px) { .cheatsheet-grid { grid-template-columns: 1fr; } }
.cheatsheet-item {
  display: flex;
  gap: 0.5rem;
  align-items: baseline;
  padding: 0.3rem 0;
  border-bottom: 1px solid var(--color-rule-soft);
  font-family: var(--font-serif);
  font-size: 0.9rem;
  color: var(--color-ink-soft);
  line-height: 1.6;
}
.cheatsheet-item:last-child { border-bottom: none; }
.cheatsheet-key {
  flex-shrink: 0;
  font-weight: 700;
  color: var(--color-ink);
  min-width: 4em;
}

/* ── 试试看 ── */
.try-it {
  background: none;
  border: none;
  border-left: 2px solid var(--color-basic);
  border-radius: 0;
  padding: 0.5rem 0 0.5rem 1.25rem;
  margin: 1.75rem 0;
}
.try-it .try-label {
  font-family: var(--font-sans);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.25em;
  color: var(--color-basic);
  text-transform: uppercase;
  margin-bottom: 0.4rem;
}
.try-it p {
  margin: 0.4rem 0;
  font-size: 0.95rem;
  font-family: var(--font-serif);
  color: var(--color-ink);
}

/* ── 小结卡片 ── */
.lesson-summary {
  background: none;
  color: var(--color-ink);
  border: none;
  border-top: 2px solid var(--color-ink);
  border-radius: 0;
  padding: 2rem 0 0;
  margin: 4rem 0 2rem;
  font-family: var(--font-serif);
  font-size: 1.05rem;
  line-height: 1.85;
}
.lesson-summary strong { color: var(--color-accent); }

/* ── 底部翻页 ── */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  margin-top: 6rem;
  padding-top: 2rem;
  border-top: 1px solid var(--color-rule);
  font-family: var(--font-sans);
}
.lesson-nav a {
  color: var(--color-ink);
  text-decoration: none;
  border: none;
  font-size: 0.75rem;
  letter-spacing: 0.15em;
  text-transform: uppercase;
  font-weight: 500;
  display: flex;
  align-items: center;
  gap: 0.4rem;
  transition: color 0.2s;
}
.lesson-nav a:hover { color: var(--color-accent); }

/* ── 书系首页/卷目录 ── */
.vol-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
  gap: 0;
  margin: 2.5rem 0;
  border-top: 1px solid var(--color-rule);
  border-left: 1px solid var(--color-rule);
}
.vol-card {
  background: var(--color-bg);
  padding: 1.75rem 1.5rem;
  border-right: 1px solid var(--color-rule);
  border-bottom: 1px solid var(--color-rule);
  text-decoration: none;
  color: inherit;
  border-radius: 0;
  box-shadow: none;
  transition: background 0.2s;
  display: block;
}
.vol-card:hover {
  background: #f3efe4;
  border-bottom-color: var(--color-rule);
}
.vol-card h3 {
  font-family: var(--font-sans);
  color: var(--color-ink-mute);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.25em;
  margin: 0 0 0.75rem;
  text-transform: uppercase;
  border: none;
  padding: 0;
}
.vol-card p {
  font-family: var(--font-serif);
  font-size: 1.05rem;
  font-weight: 500;
  color: var(--color-ink);
  line-height: 1.45;
  margin: 0;
}
.vol-card .status {
  font-family: var(--font-sans);
  font-size: 0.7rem;
  color: var(--color-ink-mute);
  margin-top: 1rem;
  letter-spacing: 0.08em;
}
.vol-card .progress-bar {
  height: 1px;
  background: var(--color-rule);
  margin-top: 0.5rem;
}
.vol-card .progress-fill {
  height: 100%;
  background: var(--color-ink);
  width: 0%;
}

/* ══════════════════════════════════════
   THEME A — 技术文档风（Stripe / Linear）
   干净白底 · 全黑体 · 有色轨道块
   ══════════════════════════════════════ */

[data-theme="A"] {
  --color-bg: #ffffff;
  --color-surface: #f8fafc;
  --color-ink: #0f172a;
  --color-ink-soft: #334155;
  --color-ink-mute: #94a3b8;
  --color-rule: #e2e8f0;
  --color-rule-soft: #f1f5f9;
  --color-accent: #4f46e5;
  --color-accent-ink: #3730a3;
  --color-basic: #16a34a;
  --color-advanced: #2563eb;
  --color-exam: #dc2626;
}

[data-theme="A"] body {
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.75;
  font-weight: 400;
}

[data-theme="A"] p { font-family: var(--font-sans); line-height: 1.75; }
[data-theme="A"] .lesson-intro {
  font-family: var(--font-sans);
  font-style: normal;
  font-size: 1.1rem;
}
[data-theme="A"] .lesson-header h1 { font-size: 2.5rem; font-weight: 700; }
[data-theme="A"] .vol-tag {
  background: var(--color-accent);
  color: #fff;
  padding: 0.2rem 0.6rem;
  border: none;
  font-size: 0.72rem;
  border-radius: 3px;
}
[data-theme="A"] h2 { font-size: 1.35rem; font-weight: 700; }
[data-theme="A"] h2::before { display: none; }
[data-theme="A"] .insight {
  font-family: var(--font-sans);
  font-size: 1rem;
  font-style: normal;
  font-weight: 500;
  background: #eff6ff;
  border-left: 3px solid var(--color-advanced);
  padding: 0.9rem 1.1rem;
}
[data-theme="A"] .insight::before { content: '💡 '; }
[data-theme="A"] blockquote {
  font-family: var(--font-sans);
  font-size: 1rem;
  font-style: normal;
  background: #f8fafc;
  padding: 1rem 1.25rem;
  border-left: 3px solid var(--color-rule);
}
[data-theme="A"] .track-basic {
  background: #f0fdf4;
  border: 1px solid #bbf7d0;
  border-left: 3px solid var(--color-basic);
  border-top: none;
  padding: 1.25rem 1.5rem;
}
[data-theme="A"] .track-advanced {
  background: #eff6ff;
  border: 1px solid #bfdbfe;
  border-left: 3px solid var(--color-advanced);
  border-top: none;
  padding: 1.25rem 1.5rem;
}
[data-theme="A"] .track-basic .track-label,
[data-theme="A"] .track-advanced .track-label {
  font-size: 0.72rem;
  border-bottom: none;
}
[data-theme="A"] .exam-point {
  background: #fef2f2;
  border: 1px solid #fecaca;
  border-left: 3px solid var(--color-exam);
  padding: 0.75rem 1rem;
  font-family: var(--font-sans);
  font-size: 0.92rem;
}
[data-theme="A"] .exam-callout {
  background: #fef2f2;
  border: 1px solid #fecaca;
  border-left: 3px solid var(--color-exam);
  padding: 0.75rem 1rem;
  font-family: var(--font-sans);
  font-size: 0.92rem;
}
[data-theme="A"] .exam-callout h2 {
  font-size: 0.72rem;
  border: none;
  padding: 0;
}
[data-theme="A"] .exam-callout h2::before { display: none; }
[data-theme="A"] table { border-top: 1px solid var(--color-rule); border-bottom: 1px solid var(--color-rule); }
[data-theme="A"] table th { background: var(--color-surface); border-bottom: 1px solid var(--color-rule); }
[data-theme="A"] table td { border-bottom: 1px solid var(--color-rule-soft); }
[data-theme="A"] .cheatsheet {
  background: var(--color-ink);
  color: #e2e8f0;
  border: none;
  border-radius: 8px;
  padding: 1.5rem 1.75rem;
}
[data-theme="A"] .cheatsheet .cheat-label { color: #818cf8; }
[data-theme="A"] .cheatsheet h3 { color: #fff; border-bottom-color: rgba(255,255,255,0.1); }
[data-theme="A"] .cheatsheet li { color: #cbd5e1; }
[data-theme="A"] .cheatsheet li strong { color: #fff; }
[data-theme="A"] .cheatsheet .tag {
  background: var(--color-accent);
  color: #fff;
  border: none;
}
[data-theme="A"] .cheatsheet .cheatsheet-item {
  color: #cbd5e1;
  border-bottom-color: rgba(255,255,255,0.08);
}
[data-theme="A"] .cheatsheet .cheatsheet-key { color: #fff; }
[data-theme="A"] .scenario { background: #f8fafc; border-left: 3px solid #e2e8f0; }
[data-theme="A"] .compare-bad { border: 1px solid #fecaca; border-top: 3px solid #ef4444; padding: 1rem 1.1rem; background: #fff5f5; }
[data-theme="A"] .compare-good { border: 1px solid #bbf7d0; border-top: 3px solid #22c55e; padding: 1rem 1.1rem; background: #f0fdf4; }
[data-theme="A"] .compare-bad .prompt-text,
[data-theme="A"] .compare-good .prompt-text { background: rgba(0,0,0,0.04); }
[data-theme="A"] .vol-grid { border: none; display: grid; grid-template-columns: repeat(auto-fill, minmax(240px,1fr)); gap: 1rem; }
[data-theme="A"] .vol-card { border: 1px solid var(--color-rule); border-top: 3px solid var(--color-accent); border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.07); }
[data-theme="A"] .vol-card h3 { color: var(--color-ink-mute); text-transform: none; letter-spacing: 0; font-size: 0.78rem; }
[data-theme="A"] .vol-card p { font-family: var(--font-sans); }
[data-theme="A"] .vol-card:hover { background: #f8fafc; }
[data-theme="A"] code { color: var(--color-accent); background: #f1f5f9; padding: 0.1em 0.35em; border-radius: 3px; }
[data-theme="A"] .quiz-toggle { border-radius: 5px; background: var(--color-accent); color: #fff; border: none; }
[data-theme="A"] .quiz-toggle:hover { background: var(--color-accent-ink); }


/* ══════════════════════════════════════
   主题切换器 UI（A / B 两款）
   ══════════════════════════════════════ */

#theme-switcher {
  position: fixed;
  bottom: 1.5rem;
  right: 1.5rem;
  z-index: 9999;
  display: flex;
  gap: 0.4rem;
  background: rgba(0,0,0,0.72);
  backdrop-filter: blur(8px);
  padding: 0.45rem 0.6rem;
  border-radius: 100px;
  box-shadow: 0 2px 12px rgba(0,0,0,0.25);
}

.theme-btn {
  width: 28px;
  height: 28px;
  border-radius: 50%;
  border: 2px solid transparent;
  cursor: pointer;
  transition: border-color 0.2s, transform 0.15s;
  display: flex; align-items: center; justify-content: center;
  font-size: 9px;
  font-weight: 700;
  line-height: 1;
}
.theme-btn:hover { transform: scale(1.12); }
.theme-btn.active { border-color: #fff; }

.theme-btn[data-t="B"] { background: #faf8f3; color: #1a1a1a; font-family: serif; }
.theme-btn[data-t="A"] { background: #ffffff; color: #0f172a; font-family: sans-serif; border-color: rgba(255,255,255,0.25); }