/* === Google Fonts === */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700;800&family=JetBrains+Mono:wght@400;500;600;700&display=swap');

/* === CSS 变量 === */
:root {
  --primary: #4F46E5;
  --primary-light: #818CF8;
  --primary-dark: #3730A3;
  --primary-bg: #EEF2FF;
  --success: #22C55E;
  --success-light: #DCFCE7;
  --success-dark: #15803d;
  --warning: #F59E0B;
  --warning-light: #FEF3C7;
  --danger: #EF4444;
  --danger-light: #FEE2E2;
  --danger-border: #FCA5A5;
  --bg: #F8FAFC;
  --card-bg: #FFFFFF;
  --text: #1E293B;
  --text-light: #64748B;
  --text-muted: #94A3B8;
  --border: #E2E8F0;
  --code-bg: #1E293B;
  --code-text: #E2E8F0;
  --shadow-sm: 0 1px 2px rgba(0,0,0,0.05);
  --shadow: 0 1px 3px rgba(0,0,0,0.05), 0 1px 2px rgba(0,0,0,0.1);
  --shadow-md: 0 4px 6px rgba(0,0,0,0.05), 0 2px 4px rgba(0,0,0,0.08);
  --shadow-lg: 0 10px 15px rgba(0,0,0,0.05), 0 4px 6px rgba(0,0,0,0.08);
  --radius-sm: 6px;
  --radius: 8px;
  --radius-md: 10px;
  --radius-lg: 12px;
  --radius-xl: 16px;
  --transition: 200ms ease;
  --transition-slow: 300ms ease;
}

/* === 全局重置 === */
*, *::before, *::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

::selection {
  background: var(--primary-light);
  color: white;
}

html {
  scroll-behavior: smooth;
}

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, "PingFang SC",
    "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.75;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

img, svg {
  max-width: 100%;
  height: auto;
  border-radius: var(--radius);
}

a {
  color: var(--primary);
  transition: color var(--transition);
}

a:hover {
  color: var(--primary-dark);
}

/* === 导航栏 === */
.navbar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: 60px;
  background: rgba(255, 255, 255, 0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid rgba(226, 232, 240, 0.8);
  display: flex;
  align-items: center;
  padding: 0 24px;
  z-index: 100;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.04);
}

.navbar-brand {
  font-weight: 700;
  font-size: 18px;
  color: var(--primary);
  text-decoration: none;
  letter-spacing: -0.3px;
  transition: color var(--transition);
}

.navbar-brand:hover {
  color: var(--primary-dark);
}

/* 汉堡按钮 */
.navbar-toggle {
  display: none;
  background: none;
  border: none;
  font-size: 22px;
  cursor: pointer;
  margin-left: auto;
  padding: 6px 10px;
  color: var(--text);
  border-radius: var(--radius-sm);
  transition: background var(--transition);
}

.navbar-toggle:hover {
  background: var(--primary-bg);
}

/* 导航菜单 */
.navbar-nav {
  display: flex;
  gap: 4px;
  margin-left: auto;
  list-style: none;
  align-items: center;
}

.navbar-nav > li {
  position: relative;
}

.navbar-nav > li > a {
  color: var(--text-light);
  text-decoration: none;
  padding: 10px 14px;
  border-radius: var(--radius);
  font-size: 14px;
  font-weight: 500;
  cursor: pointer;
  transition: background var(--transition), color var(--transition);
  white-space: nowrap;
  display: inline-block;
}

.navbar-nav > li > a:hover {
  background: var(--primary-bg);
  color: var(--primary);
}

.navbar-nav > li > a.active {
  background: var(--primary);
  color: #fff;
}

/* === 主内容区 === */
.main {
  max-width: 820px;
  margin: 0 auto;
  padding: 84px 24px 60px;
}

/* 有侧边栏时偏移（见 .has-sidebar 在侧边栏区块定义） */

/* === 首页 Hero === */
.hero {
  text-align: center;
  padding: 60px 0 48px;
  background: linear-gradient(180deg, var(--primary-bg) 0%, var(--bg) 100%);
  border-radius: var(--radius-xl);
  margin: -24px -24px 16px;
  padding-left: 24px;
  padding-right: 24px;
}

.hero h1 {
  font-size: 40px;
  font-weight: 800;
  color: var(--text);
  margin-bottom: 12px;
  letter-spacing: -0.5px;
}

.hero p {
  font-size: 18px;
  color: var(--text-light);
  max-width: 540px;
  margin: 0 auto 40px;
  line-height: 1.7;
}

/* === 课程卡片 === */
.chapter-cards {
  display: grid;
  grid-template-columns: 1fr;
  gap: 16px;
  max-width: 620px;
  margin: 0 auto;
}

.chapter-card {
  display: flex;
  align-items: center;
  gap: 20px;
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 24px;
  text-decoration: none;
  color: var(--text);
  transition: transform var(--transition), box-shadow var(--transition), border-color var(--transition);
  box-shadow: var(--shadow-sm);
}

.chapter-card:hover {
  transform: translateY(-2px);
  border-color: var(--primary-light);
  box-shadow: var(--shadow-md);
}

.chapter-card.disabled {
  opacity: 0.55;
  cursor: default;
}

.chapter-card.disabled:hover {
  transform: none;
  border-color: var(--border);
  box-shadow: var(--shadow-sm);
}

.chapter-num {
  flex-shrink: 0;
  width: 48px;
  height: 48px;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--primary), var(--primary-light));
  color: #fff;
  font-weight: 700;
  font-size: 20px;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: 0 2px 8px rgba(79, 70, 229, 0.25);
}

.chapter-card.disabled .chapter-num {
  background: linear-gradient(135deg, #94a3b8, #cbd5e1);
  box-shadow: none;
}

.chapter-card h3 {
  font-size: 17px;
  font-weight: 600;
  margin-bottom: 4px;
  line-height: 1.4;
}

.chapter-card p {
  font-size: 14px;
  color: var(--text-light);
  line-height: 1.5;
}

.chapter-card .coming-soon {
  font-size: 11px;
  color: var(--text-muted);
  background: #f1f5f9;
  padding: 2px 8px;
  border-radius: var(--radius);
  margin-left: 8px;
  font-weight: 500;
  letter-spacing: 0.3px;
}

/* === 章节页面头部 === */
.chapter-header {
  padding: 40px 0 32px;
  border-bottom: 2px solid var(--primary);
  margin-bottom: 36px;
}

.chapter-header .label {
  font-size: 13px;
  color: var(--primary);
  font-weight: 600;
  letter-spacing: 1.5px;
  text-transform: uppercase;
}

.chapter-header h1 {
  font-size: 32px;
  font-weight: 800;
  margin-top: 8px;
  letter-spacing: -0.3px;
}

.chapter-meta {
  display: flex;
  gap: 16px;
  font-size: 14px;
  color: var(--text-light);
  margin-top: 10px;
}

.chapter-meta span {
  display: inline-flex;
  align-items: center;
  gap: 4px;
}

/* === 内容区块 === */
.content-section {
  margin-bottom: 48px;
}

.content-section h2 {
  font-size: 24px;
  font-weight: 700;
  margin-bottom: 16px;
  color: var(--text);
  padding-bottom: 10px;
  border-bottom: 1px solid var(--border);
  line-height: 1.4;
}

.content-section h3 {
  font-size: 20px;
  font-weight: 600;
  margin-bottom: 12px;
  margin-top: 28px;
  line-height: 1.4;
}

.content-section h4 {
  font-size: 17px;
  font-weight: 600;
  margin-bottom: 10px;
  margin-top: 20px;
}

.content-section p {
  margin-bottom: 16px;
  line-height: 1.8;
}

.content-section ul,
.content-section ol {
  margin: 0 0 16px 24px;
}

.content-section li {
  margin-bottom: 8px;
  line-height: 1.75;
}

/* === 高亮框 === */
.highlight-box {
  background: var(--primary-bg);
  border-left: 4px solid var(--primary);
  padding: 16px 20px;
  border-radius: 0 var(--radius) var(--radius) 0;
  margin: 24px 0;
}

.highlight-box strong {
  color: var(--primary-dark);
}

/* === 信息卡片 === */
.info-card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 24px;
  margin: 24px 0;
  box-shadow: var(--shadow-sm);
}

/* === 表格 === */
.table-wrap {
  overflow-x: auto;
  margin: 24px 0;
  border-radius: var(--radius);
  box-shadow: var(--shadow-sm);
}

table {
  width: 100%;
  border-collapse: collapse;
  background: var(--card-bg);
  border-radius: var(--radius);
  overflow: hidden;
  border: 1px solid var(--border);
}

th, td {
  padding: 12px 16px;
  text-align: left;
  border-bottom: 1px solid var(--border);
  font-size: 15px;
}

th {
  background: var(--primary);
  color: #fff;
  font-weight: 600;
  font-size: 14px;
  letter-spacing: 0.3px;
}

tr:last-child td {
  border-bottom: none;
}

tr:nth-child(even) td {
  background: #f8fafc;
}

/* === 代码块 === */
.code-block {
  position: relative;
  margin: 24px 0;
  border-radius: var(--radius-md);
  overflow: hidden;
  background: var(--code-bg);
  box-shadow: var(--shadow);
}

.code-block .code-lang {
  position: absolute;
  top: 0;
  left: 0;
  font-size: 11px;
  color: var(--code-bg);
  background: var(--text-muted);
  font-family: 'JetBrains Mono', 'SF Mono', Consolas, monospace;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.8px;
  z-index: 2;
  padding: 4px 12px;
  border-radius: 0 0 var(--radius-sm) 0;
}

.code-block .copy-btn {
  position: absolute;
  top: 8px;
  right: 8px;
  background: rgba(255, 255, 255, 0.08);
  border: 1px solid rgba(255, 255, 255, 0.12);
  color: var(--text-muted);
  padding: 4px 12px;
  border-radius: var(--radius-sm);
  font-size: 12px;
  font-family: 'Inter', sans-serif;
  cursor: pointer;
  transition: background var(--transition), color var(--transition);
  z-index: 2;
  opacity: 0;
}

.code-block:hover .copy-btn {
  opacity: 1;
}

.code-block .copy-btn:hover {
  background: rgba(255, 255, 255, 0.18);
  color: #e2e8f0;
}

.code-block .copy-btn.copied {
  color: var(--success);
  border-color: rgba(34, 197, 94, 0.4);
}

.code-block pre {
  margin: 0;
  padding: 40px 20px 20px;
  overflow-x: auto;
  background: var(--code-bg) !important;
}

.code-block pre code {
  font-family: 'JetBrains Mono', 'SF Mono', 'Fira Code', Consolas, 'Courier New', monospace;
  font-size: 14px;
  line-height: 1.6;
  tab-size: 4;
}

/* 行内代码 */
code:not([class*="language-"]) {
  background: #f1f5f9;
  color: var(--primary-dark);
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 0.88em;
  font-family: 'JetBrains Mono', 'SF Mono', Consolas, monospace;
  font-weight: 500;
}

/* === ASCII 图专用样式 === */
.ascii-diagram {
  position: relative;
  margin: 24px 0;
  border-radius: var(--radius);
  overflow: hidden;
}

.ascii-diagram pre {
  margin: 0;
  padding: 20px;
  background: #f0f4ff !important;
  border: 1px solid #c7d2fe;
  border-radius: var(--radius);
  overflow-x: auto;
  white-space: pre;
}

.ascii-diagram pre code {
  font-family: 'JetBrains Mono', 'SF Mono', Consolas, monospace;
  font-size: 14px;
  line-height: 1.5;
  color: var(--text);
}

/* === 公式框 === */
.formula-box {
  background: var(--primary-bg);
  border: 1px solid #c7d2fe;
  border-radius: var(--radius-md);
  padding: 16px 24px;
  margin: 24px 0;
  font-family: 'JetBrains Mono', 'SF Mono', Consolas, monospace;
  font-size: 15px;
  line-height: 1.8;
  text-align: center;
}

.formula-box .formula-title {
  font-family: 'Inter', sans-serif;
  font-weight: 700;
  color: var(--primary-dark);
  margin-bottom: 8px;
  font-size: 13px;
  text-transform: uppercase;
  letter-spacing: 0.8px;
}

/* === 警告框 === */
.warning-box {
  background: var(--danger-light);
  border-left: 4px solid var(--danger);
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: 16px 20px;
  margin: 24px 0;
}

.warning-box .warning-title {
  font-weight: 700;
  color: var(--danger);
  margin-bottom: 8px;
  font-size: 15px;
}

.warning-box p {
  margin-bottom: 8px;
}

.warning-box p:last-child {
  margin-bottom: 0;
}

.warning-box code {
  background: rgba(239, 68, 68, 0.1);
}

/* === 对比表 === */
.comparison-table {
  margin: 24px 0;
  border: 2px solid var(--primary);
  border-radius: var(--radius-lg);
  overflow: hidden;
  box-shadow: var(--shadow);
}

.comparison-table table {
  border: none;
  border-radius: 0;
}

.comparison-table th {
  background: var(--primary);
  text-align: center;
}

.comparison-table td {
  vertical-align: top;
}

.comparison-table tr:nth-child(even) td {
  background: #f8fafc;
}

/* === 难度标签 === */
.badge {
  display: inline-block;
  padding: 3px 12px;
  border-radius: var(--radius-lg);
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.3px;
  vertical-align: middle;
}

.badge-required {
  background: var(--success);
  color: #fff;
}

.badge-practical {
  background: var(--warning);
  color: #78350f;
}

.badge-advanced {
  background: var(--primary);
  color: #fff;
}

/* === 手风琴 === */
.accordion {
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  overflow: hidden;
  margin: 24px 0;
  box-shadow: var(--shadow-sm);
}

.accordion-item {
  border-bottom: 1px solid var(--border);
}

.accordion-item:last-child {
  border-bottom: none;
}

.accordion-btn {
  width: 100%;
  text-align: left;
  padding: 16px 20px;
  background: var(--card-bg);
  border: none;
  cursor: pointer;
  font-size: 15px;
  font-weight: 600;
  font-family: 'Inter', sans-serif;
  color: var(--text);
  display: flex;
  align-items: center;
  gap: 12px;
  transition: background var(--transition);
}

.accordion-btn:hover {
  background: var(--primary-bg);
}

.accordion-btn::before {
  content: "";
  display: inline-block;
  width: 0;
  height: 0;
  border-left: 6px solid var(--primary);
  border-top: 5px solid transparent;
  border-bottom: 5px solid transparent;
  transition: transform var(--transition);
  flex-shrink: 0;
}

.accordion-item.open .accordion-btn::before {
  transform: rotate(90deg);
}

.accordion-content {
  max-height: 0;
  overflow: hidden;
  transition: max-height var(--transition-slow);
  padding: 0 20px 0 48px;
  color: var(--text-light);
  line-height: 1.7;
}

.accordion-item.open .accordion-content {
  max-height: 800px;
  padding-bottom: 16px;
}

/* === 进度条 === */
.progress-bar {
  background: #e2e8f0;
  border-radius: 20px;
  height: 6px;
  margin: 16px 0 8px;
  overflow: hidden;
  box-shadow: inset 0 1px 2px rgba(0, 0, 0, 0.06);
}

.progress-bar .fill {
  height: 100%;
  background: linear-gradient(90deg, var(--primary), var(--success));
  border-radius: 20px;
  transition: width 0.5s ease;
  width: 0%;
}

.progress-info {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 13px;
  color: var(--text-light);
  margin-bottom: 24px;
}

.progress-info .reset-link {
  color: var(--text-muted);
  text-decoration: none;
  cursor: pointer;
  border: none;
  background: none;
  font-size: 12px;
  font-family: 'Inter', sans-serif;
  transition: color var(--transition);
}

.progress-info .reset-link:hover {
  color: var(--primary);
}

/* === 检查点（旧样式 - 手动确认） === */
.checkpoint {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-left: 4px solid var(--primary);
  border-radius: 0 var(--radius-lg) var(--radius-lg) 0;
  padding: 16px 20px;
  margin: 24px 0;
  display: flex;
  align-items: flex-start;
  gap: 14px;
  box-shadow: var(--shadow-sm);
  transition: border-color var(--transition-slow), background var(--transition-slow);
}

.checkpoint-icon {
  font-size: 14px;
  flex-shrink: 0;
  line-height: 1;
  width: 32px;
  height: 32px;
  background: var(--primary);
  color: #fff;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
}

.checkpoint-body {
  flex: 1;
}

.checkpoint-body strong {
  display: block;
  color: var(--primary-dark);
  margin-bottom: 4px;
  font-size: 15px;
}

.checkpoint-body p {
  font-size: 14px;
  color: var(--text-light);
  margin: 0;
}

.checkpoint-btn {
  background: var(--primary);
  color: #fff;
  border: none;
  border-radius: var(--radius-sm);
  padding: 6px 16px;
  font-size: 14px;
  font-weight: 500;
  font-family: 'Inter', sans-serif;
  cursor: pointer;
  margin-top: 8px;
  transition: background var(--transition);
}

.checkpoint-btn:hover {
  background: var(--primary-dark);
}

.checkpoint.done {
  background: var(--success-light);
  border-left-color: var(--success);
}

.checkpoint.done .checkpoint-btn {
  display: none;
}

.checkpoint.done .checkpoint-icon {
  background: var(--success);
}

.checkpoint.done::after {
  content: "已完成";
  font-size: 14px;
  font-weight: 600;
  color: var(--success-dark);
  align-self: center;
}

/* === 答题验证检查点 === */
.checkpoint-quiz {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-left: 4px solid var(--primary);
  border-radius: 0 var(--radius-lg) var(--radius-lg) 0;
  padding: 20px 24px;
  margin: 24px 0;
  box-shadow: var(--shadow-sm);
  transition: border-color var(--transition-slow), background var(--transition-slow);
}

.checkpoint-quiz .checkpoint-header {
  margin-bottom: 12px;
}

.checkpoint-quiz .checkpoint-icon-text {
  font-weight: 700;
  color: var(--primary-dark);
  font-size: 13px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  background: var(--primary-bg);
  padding: 3px 10px;
  border-radius: var(--radius);
  display: inline-block;
}

.checkpoint-quiz .checkpoint-question {
  font-size: 16px;
  font-weight: 600;
  color: var(--text);
  margin-bottom: 16px;
  line-height: 1.6;
}

.checkpoint-quiz .checkpoint-options {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.checkpoint-quiz .quiz-option {
  display: block;
  width: 100%;
  text-align: left;
  padding: 12px 16px;
  background: #f8fafc;
  border: 2px solid var(--border);
  border-radius: var(--radius);
  font-size: 15px;
  font-family: 'Inter', sans-serif;
  color: var(--text);
  cursor: pointer;
  transition: border-color var(--transition), background var(--transition), transform 100ms ease;
  line-height: 1.5;
}

.checkpoint-quiz .quiz-option:hover:not(.selected):not(.disabled) {
  border-color: var(--primary-light);
  background: var(--primary-bg);
  transform: translateX(2px);
}

.checkpoint-quiz .quiz-option.selected.correct {
  border-color: var(--success);
  background: var(--success-light);
  color: #166534;
  font-weight: 600;
}

.checkpoint-quiz .quiz-option.selected.wrong {
  border-color: var(--danger);
  background: var(--danger-light);
  color: #991b1b;
}

.checkpoint-quiz .quiz-option.show-correct {
  border-color: var(--success);
  background: var(--success-light);
}

.checkpoint-quiz .quiz-option.disabled {
  cursor: default;
  opacity: 0.6;
}

/* 填空题输入 */
.checkpoint-quiz .checkpoint-input {
  display: flex;
  gap: 12px;
  align-items: center;
}

.checkpoint-quiz .checkpoint-input input {
  border: 2px solid var(--border);
  border-radius: var(--radius);
  padding: 10px 14px;
  font-size: 16px;
  width: 180px;
  font-family: 'JetBrains Mono', 'SF Mono', Consolas, monospace;
  transition: border-color var(--transition), box-shadow var(--transition);
}

.checkpoint-quiz .checkpoint-input input:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(79, 70, 229, 0.12);
}

.checkpoint-quiz .checkpoint-input input.correct {
  border-color: var(--success);
  background: var(--success-light);
}

.checkpoint-quiz .checkpoint-input input.wrong {
  border-color: var(--danger);
  background: var(--danger-light);
}

.checkpoint-quiz .quiz-submit {
  background: var(--primary);
  color: #fff;
  border: none;
  border-radius: var(--radius);
  padding: 10px 20px;
  font-size: 15px;
  font-weight: 600;
  font-family: 'Inter', sans-serif;
  cursor: pointer;
  transition: background var(--transition);
}

.checkpoint-quiz .quiz-submit:hover {
  background: var(--primary-dark);
}

.checkpoint-quiz .quiz-submit:disabled {
  background: var(--text-muted);
  cursor: default;
}

.checkpoint-quiz .checkpoint-feedback {
  margin-top: 12px;
  padding: 12px 16px;
  border-radius: var(--radius);
  font-size: 14px;
  line-height: 1.6;
}

.checkpoint-quiz .checkpoint-feedback.correct {
  background: var(--success-light);
  border: 1px solid #86efac;
  color: #166534;
}

.checkpoint-quiz .checkpoint-feedback.wrong {
  background: var(--danger-light);
  border: 1px solid var(--danger-border);
  color: #991b1b;
}

.checkpoint-quiz .checkpoint-success {
  margin-top: 12px;
  color: #166534;
  font-weight: 700;
  font-size: 15px;
}

.checkpoint-quiz.done {
  opacity: 0.7;
  border-left-color: var(--success);
  background: var(--success-light);
}

/* === 测验框 === */
.quiz-box {
  background: var(--primary-bg);
  border: 1px solid #c7d2fe;
  border-radius: var(--radius-lg);
  padding: 24px;
  margin: 24px 0;
  box-shadow: var(--shadow-sm);
}

.quiz-box h3 {
  color: var(--primary-dark);
  margin-bottom: 12px;
}

.quiz-box .quiz-question {
  margin-bottom: 12px;
  font-weight: 500;
}

.quiz-box input[type="text"] {
  border: 2px solid var(--border);
  border-radius: var(--radius);
  padding: 8px 12px;
  font-size: 16px;
  width: 200px;
  font-family: 'JetBrains Mono', Consolas, monospace;
  transition: border-color var(--transition), box-shadow var(--transition);
}

.quiz-box input[type="text"]:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(79, 70, 229, 0.12);
}

.quiz-box .quiz-options {
  list-style: none;
  padding: 0;
  margin: 12px 0;
}

.quiz-box .quiz-options li {
  margin-bottom: 8px;
}

.quiz-box .quiz-options label {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 10px 14px;
  border-radius: var(--radius);
  cursor: pointer;
  transition: background var(--transition);
}

.quiz-box .quiz-options label:hover {
  background: rgba(79, 70, 229, 0.08);
}

.quiz-box button {
  background: var(--primary);
  color: #fff;
  border: none;
  border-radius: var(--radius);
  padding: 8px 20px;
  font-size: 15px;
  font-weight: 500;
  font-family: 'Inter', sans-serif;
  cursor: pointer;
  margin-top: 12px;
  transition: background var(--transition);
}

.quiz-box button:hover {
  background: var(--primary-dark);
}

.quiz-box .result {
  margin-top: 12px;
  font-weight: 600;
}

.quiz-box .result.correct {
  color: var(--success);
}

.quiz-box .result.wrong {
  color: var(--danger);
}

/* === 练习答案折叠 === */
.answer-toggle {
  display: inline-block;
  background: var(--primary);
  color: #fff;
  border: none;
  border-radius: var(--radius);
  padding: 8px 20px;
  font-size: 14px;
  font-weight: 500;
  font-family: 'Inter', sans-serif;
  cursor: pointer;
  margin: 12px 0;
  transition: background var(--transition);
}

.answer-toggle:hover {
  background: var(--primary-dark);
}

.answer-content {
  display: none;
  background: #f8fafc;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px 20px;
  margin: 8px 0 16px;
}

.answer-content.show {
  display: block;
}

/* details/summary 折叠答案 */
details {
  margin: 16px 0;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
}

details summary {
  padding: 12px 20px;
  background: #f8fafc;
  cursor: pointer;
  font-weight: 600;
  color: var(--primary);
  transition: background var(--transition);
  list-style: none;
}

details summary::-webkit-details-marker {
  display: none;
}

details summary::before {
  content: "";
  display: inline-block;
  width: 0;
  height: 0;
  border-left: 6px solid var(--primary);
  border-top: 4px solid transparent;
  border-bottom: 4px solid transparent;
  margin-right: 10px;
  transition: transform var(--transition);
  vertical-align: middle;
}

details[open] summary::before {
  transform: rotate(90deg);
}

details summary:hover {
  background: var(--primary-bg);
}

details .details-content {
  padding: 16px 20px;
  background: #fff;
}

/* === 底部翻页导航 === */
.page-nav {
  display: flex;
  justify-content: space-between;
  align-items: stretch;
  gap: 16px;
  margin-top: 24px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
}

.page-nav-link {
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 20px 24px;
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  text-decoration: none;
  color: var(--text);
  transition: border-color var(--transition), box-shadow var(--transition), transform var(--transition);
  min-width: 0;
  flex: 1;
  max-width: 48%;
}

.page-nav-link:hover {
  border-color: var(--primary-light);
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
  color: var(--text);
}

.page-nav-link.next {
  text-align: right;
  margin-left: auto;
}

.page-nav-label {
  font-size: 12px;
  color: var(--text-muted);
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.page-nav-title {
  font-size: 16px;
  font-weight: 600;
  color: var(--primary);
}

.page-nav-link:hover .page-nav-title {
  color: var(--primary-dark);
}

.page-nav-placeholder {
  flex: 1;
  max-width: 48%;
}

/* === 全局课程侧边栏 === */
.book-sidebar {
  position: fixed;
  top: 60px;
  left: 0;
  width: 260px;
  height: calc(100vh - 60px);
  overflow-y: auto;
  background: #fff;
  border-right: 1px solid var(--border);
  padding: 20px 0 60px;
  z-index: 50;
  font-size: 14px;
}

.book-sidebar::-webkit-scrollbar {
  width: 4px;
}

.book-sidebar::-webkit-scrollbar-thumb {
  background: #e2e8f0;
  border-radius: 4px;
}

.book-sidebar::-webkit-scrollbar-thumb:hover {
  background: #cbd5e1;
}

/* 顶部书名 */
.sidebar-title {
  display: block;
  padding: 0 20px 16px;
  font-weight: 700;
  font-size: 16px;
  color: var(--primary);
  text-decoration: none;
  border-bottom: 1px solid var(--border);
  margin-bottom: 12px;
  transition: color var(--transition);
}

.sidebar-title:hover {
  color: var(--primary-dark);
}

/* 分组标题（如 Level 5 · 底盘运动控制） */
.sidebar-section {
  padding: 12px 20px 6px;
  font-size: 12px;
  font-weight: 600;
  color: var(--text-light);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  border-top: 1px solid var(--border);
  margin-top: 8px;
}

.sidebar-section:first-of-type {
  border-top: none;
  margin-top: 0;
}

/* 可点击的课程项 */
.sidebar-item {
  display: block;
  padding: 6px 20px;
  color: var(--text-light);
  text-decoration: none;
  font-size: 14px;
  font-weight: 500;
  border-left: 3px solid transparent;
  transition: all var(--transition);
  line-height: 1.5;
}

.sidebar-item:hover {
  color: var(--primary);
  background: var(--primary-bg);
}

/* 当前页面高亮 */
.sidebar-item.active {
  color: var(--primary);
  background: var(--primary-bg);
  border-left-color: var(--primary);
  font-weight: 600;
}

/* 灰色不可用项 */
.sidebar-item.disabled {
  color: #CBD5E1;
  cursor: default;
  pointer-events: none;
}

/* 子目录项缩进 */
.sidebar-item.sub-page {
  padding-left: 36px;
  font-size: 13px;
}

/* 页内小节列表 */
.sidebar-sub {
  list-style: none;
  padding: 0;
  margin: 0;
  overflow: hidden;
  max-height: 0;
  transition: max-height 0.3s ease;
}

.sidebar-sub.expanded {
  max-height: 1000px;
}

.sidebar-sub .sub-item {
  display: block;
  padding: 8px 20px 8px 44px;
  color: var(--text-muted);
  text-decoration: none;
  font-size: 13px;
  line-height: 1.6;
  border-left: 3px solid transparent;
  transition: all var(--transition);
}

.sidebar-sub .sub-item:hover {
  color: var(--primary);
  background: var(--primary-bg);
}

/* 滚动高亮的当前小节 */
.sidebar-sub .sub-item.current {
  color: var(--primary);
  border-left-color: var(--primary);
  background: var(--primary-bg);
  font-weight: 500;
}

/* 有侧边栏时主内容偏移 */
.has-sidebar .main {
  margin-left: 260px;
  max-width: none;
  padding-right: 24px;
}

.has-sidebar .main > *:not(.page-nav) {
  max-width: 820px;
}

/* 移动端侧边栏按钮 */
.sidebar-mobile-toggle {
  display: none;
  position: fixed;
  bottom: 20px;
  right: 20px;
  width: 48px;
  height: 48px;
  border-radius: 50%;
  background: var(--primary);
  color: #fff;
  border: none;
  font-size: 20px;
  cursor: pointer;
  z-index: 90;
  box-shadow: var(--shadow-lg);
  transition: background var(--transition), transform var(--transition);
  align-items: center;
  justify-content: center;
}

.sidebar-mobile-toggle:hover {
  background: var(--primary-dark);
  transform: scale(1.05);
}

/* 移动端遮罩 */
.sidebar-overlay {
  display: none;
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(0, 0, 0, 0.4);
  z-index: 89;
}

.sidebar-overlay.show {
  display: block;
}

/* 引用块 */
blockquote {
  background: #f8fafc;
  border-left: 4px solid var(--primary);
  padding: 12px 20px;
  margin: 20px 0;
  border-radius: 0 var(--radius) var(--radius) 0;
  color: var(--text-light);
  font-size: 15px;
}

blockquote strong {
  color: var(--text);
}

/* === 页脚 === */
.site-footer {
  text-align: center;
  padding: 32px 24px;
  color: var(--text-muted);
  font-size: 13px;
  border-top: 1px solid var(--border);
  margin-top: 48px;
}

/* === 响应式 === */

@media (max-width: 800px) {
  .navbar-toggle {
    display: block;
  }

  .navbar-nav {
    display: none;
    position: fixed;
    top: 60px;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(255, 255, 255, 0.98);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    flex-direction: column;
    padding: 16px;
    gap: 0;
    overflow-y: auto;
    border-top: 1px solid var(--border);
    animation: slideDown var(--transition-slow);
  }

  @keyframes slideDown {
    from {
      opacity: 0;
      transform: translateY(-8px);
    }
    to {
      opacity: 1;
      transform: translateY(0);
    }
  }

  .navbar-nav.open {
    display: flex;
  }

  .navbar-nav > li {
    border-bottom: 1px solid #f0f0f0;
  }

  .navbar-nav > li > a {
    padding: 14px 12px;
    font-size: 15px;
    width: 100%;
    text-align: left;
    display: block;
  }

  /* 移动端：隐藏侧边栏，显示目录按钮 */
  .book-sidebar {
    transform: translateX(-100%);
    transition: transform 0.3s ease;
  }

  .book-sidebar.mobile-open {
    transform: translateX(0);
    box-shadow: var(--shadow-lg);
  }

  .sidebar-mobile-toggle {
    display: flex;
  }

  .has-sidebar .main {
    margin-left: 0;
  }

  /* 翻页导航移动端 */
  .page-nav {
    flex-direction: column;
    gap: 12px;
  }

  .page-nav-link,
  .page-nav-placeholder {
    max-width: 100%;
  }

  .page-nav-link.next {
    text-align: left;
  }
}

/* === Toast 通知 === */
.toast {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%) translateY(100px);
  background: var(--code-bg);
  color: #fff;
  padding: 12px 24px;
  border-radius: var(--radius);
  font-size: 14px;
  font-family: 'Inter', sans-serif;
  z-index: 9999;
  opacity: 0;
  transition: all var(--transition-slow);
  pointer-events: none;
  box-shadow: var(--shadow-lg);
}

.toast.show {
  transform: translateX(-50%) translateY(0);
  opacity: 1;
}

/* === 小屏幕适配 === */
@media (max-width: 640px) {
  .navbar {
    padding: 0 16px;
  }

  .main {
    padding: 76px 16px 40px;
  }

  .hero {
    margin: -16px -16px 24px;
    padding: 40px 16px;
  }

  .hero h1 {
    font-size: 28px;
  }

  .hero p {
    font-size: 16px;
  }

  .chapter-card {
    padding: 16px;
    gap: 14px;
  }

  .chapter-header h1 {
    font-size: 26px;
  }

  .code-block pre {
    padding: 36px 12px 12px;
  }

  .code-block pre code {
    font-size: 13px;
  }

  .code-block .copy-btn {
    opacity: 1;
  }

  .comparison-table {
    font-size: 14px;
  }

  .comparison-table td,
  .comparison-table th {
    padding: 8px 10px;
  }

  .checkpoint-quiz {
    padding: 16px;
  }

  .content-section h2 {
    font-size: 21px;
  }

  .content-section h3 {
    font-size: 18px;
  }
}

/* === SVG 最小宽度（防止数学基础页面图表在小屏被压缩） === */
.content-section svg {
  min-width: 300px;
}

/* === Prism.js 行号样式（深色代码块兼容） === */
.line-numbers .line-numbers-rows {
  border-right: 1px solid #374151;
}
.line-numbers .line-numbers-rows > span::before {
  color: #6B7280;
}

/* === 侧边栏学习进度标签 === */
.sidebar-progress {
  font-size: 11px;
  color: var(--text-muted);
  margin-left: 4px;
}
.sidebar-progress.complete {
  color: var(--success);
  font-weight: 600;
}

/* === 自动书签横条 === */
.bookmark-bar {
  position: fixed;
  top: 60px;
  left: 0;
  right: 0;
  z-index: 90;
  background: var(--primary-bg);
  border-bottom: 1px solid var(--primary-light);
  padding: 10px 24px;
  display: flex;
  align-items: center;
  gap: 12px;
  font-size: 14px;
  color: var(--text);
  transform: translateY(-100%);
  opacity: 0;
  transition: transform 0.3s ease, opacity 0.3s ease;
}
.bookmark-bar.show {
  transform: translateY(0);
  opacity: 1;
}
.bookmark-bar span {
  flex: 1;
}
.bookmark-resume {
  background: var(--primary);
  color: white;
  border: none;
  padding: 6px 16px;
  border-radius: var(--radius);
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  transition: background var(--transition);
}
.bookmark-resume:hover {
  background: var(--primary-dark);
}
.bookmark-dismiss {
  background: none;
  border: none;
  color: var(--text-muted);
  font-size: 13px;
  cursor: pointer;
  padding: 6px 8px;
}
.bookmark-dismiss:hover {
  color: var(--text);
}

/* 有侧边栏时书签条偏移 */
.has-sidebar .bookmark-bar {
  left: 260px;
}
@media (max-width: 800px) {
  .has-sidebar .bookmark-bar {
    left: 0;
  }
  .bookmark-bar {
    flex-wrap: wrap;
  }
}

/* === 章节完成标记 === */
.section-check {
  font-size: 12px;
  margin-left: 4px;
}

/* === 首页继续学习按钮 === */
.continue-btn {
  display: inline-block;
  padding: 14px 32px;
  background: var(--primary);
  color: white;
  text-decoration: none;
  border-radius: var(--radius-lg);
  font-size: 17px;
  font-weight: 700;
  transition: transform var(--transition), box-shadow var(--transition), background var(--transition);
  box-shadow: 0 4px 12px rgba(79, 70, 229, 0.3);
}
.continue-btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 16px rgba(79, 70, 229, 0.4);
  background: var(--primary-dark);
  color: white;
}
.continue-btn.start {
  background: var(--success);
  box-shadow: 0 4px 12px rgba(34, 197, 94, 0.3);
}
.continue-btn.start:hover {
  background: var(--success-dark);
  box-shadow: 0 6px 16px rgba(34, 197, 94, 0.4);
}

/* 视频推荐卡片 */
.video-recommend {
  margin: 1.5rem 0;
  padding: 1rem 1.25rem;
  background: #fef9f0;
  border: 1px solid #f0e0c0;
  border-radius: 12px;
  border-left: 4px solid #e8734a;
}
.video-recommend-title {
  font-size: 0.85rem;
  font-weight: 600;
  color: #e8734a;
  margin-bottom: 0.5rem;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}
/* 视频卡片（点击展开播放） */
.video-card {
  cursor: pointer;
  padding: 0.5rem 0;
  border-bottom: 1px solid rgba(0,0,0,0.06);
}
.video-card:last-of-type {
  border-bottom: none;
  padding-bottom: 0;
}
.video-card .video-thumb {
  width: 100%;
  aspect-ratio: 16 / 9;
  background-size: cover;
  background-position: center;
  border-radius: 8px;
  position: relative;
  margin-bottom: 0.5rem;
}
.video-card .video-thumb:hover {
  filter: brightness(0.9);
}
.video-card .video-play-btn {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 56px;
  height: 56px;
  background: rgba(255, 0, 0, 0.85);
  border-radius: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
  font-size: 1.2rem;
  transition: transform 0.15s, background 0.15s;
}
.video-card .video-thumb:hover .video-play-btn {
  background: rgba(255, 0, 0, 1);
  transform: translate(-50%, -50%) scale(1.08);
}
.video-card .video-info {
  flex: 1;
  min-width: 0;
}
.video-card .video-name {
  font-size: 0.9rem;
  font-weight: 500;
  line-height: 1.4;
  color: #333;
}
.video-card .video-meta {
  font-size: 0.78rem;
  color: #888;
  margin-top: 2px;
}
/* 展开后的 iframe 容器 */
.video-card .video-embed {
  width: 100%;
  aspect-ratio: 16 / 9;
  border-radius: 8px;
  overflow: hidden;
  margin-bottom: 0.5rem;
}
.video-card .video-embed iframe {
  width: 100%;
  height: 100%;
  border: none;
}
@media (max-width: 640px) {
  .video-recommend {
    padding: 0.75rem 1rem;
  }
  .video-card .video-play-btn {
    width: 44px;
    height: 44px;
    font-size: 1rem;
  }
}

/* 参考图片 */
.ref-figure {
  margin: 1.5rem 0;
  text-align: center;
}
.ref-figure img {
  max-width: 100%;
  border: 1px solid #e0e0e0;
  border-radius: 8px;
  box-shadow: 0 2px 8px rgba(0,0,0,0.08);
}
.ref-figure figcaption {
  font-size: 0.8rem;
  color: #888;
  margin-top: 0.5rem;
  font-style: italic;
}

/* 扩展资料区块 */
.resources-box {
  margin: 2rem 0;
  padding: 1.25rem;
  background: #f0f4ff;
  border: 1px solid #d0d8f0;
  border-radius: 12px;
}
.resources-box-title {
  font-size: 0.9rem;
  font-weight: 700;
  color: var(--primary);
  margin-bottom: 0.75rem;
}
.resources-box ul {
  list-style: none;
  padding: 0;
  margin: 0;
}
.resources-box li {
  padding: 0.4rem 0;
  border-bottom: 1px solid rgba(0,0,0,0.06);
  font-size: 0.88rem;
}
.resources-box li:last-child {
  border-bottom: none;
}
.resources-box a {
  color: var(--primary);
  text-decoration: none;
}
.resources-box a:hover {
  text-decoration: underline;
}
.resources-box .res-tag {
  display: inline-block;
  font-size: 0.7rem;
  padding: 1px 6px;
  border-radius: 4px;
  margin-right: 0.3rem;
  font-weight: 600;
}
.res-tag.pdf { background: #fee2e2; color: #dc2626; }
.res-tag.video { background: #fef3c7; color: #d97706; }
.res-tag.cn { background: #dbeafe; color: #2563eb; }
.res-tag.en { background: #f0fdf4; color: #16a34a; }