/* ================================================================
   中国网储系统性学习手册 · 全局样式
   版本：v1.0 | 适用于导览页 index.html 及全部 287 个章节 HTML
   ================================================================ */

/* ── Google Fonts 请在 HTML <head> 中引入 ─────────────────────── */
/* <link href="https://fonts.googleapis.com/css2?family=Noto+Sans+SC:wght@400;500;600;700&family=Inter:wght@400;500;700&family=JetBrains+Mono&display=swap" rel="stylesheet"> */

/* ── 1. CSS 变量（Design Tokens）────────────────────────────────── */
:root {
  /* 主色板 */
  --c-primary:        #1A5F96;
  --c-primary-dark:   #0D3F6F;
  --c-primary-light:  #E8F2FF;
  --c-secondary:      #0A8A5F;
  --c-accent:         #F57C00;
  --c-danger:         #DC2626;
  --c-warning:        #D97706;
  --c-success:        #059669;

  /* 文字 */
  --c-text-primary:   #1A1A2E;
  --c-text-secondary: #4A5568;
  --c-text-muted:     #718096;
  --c-text-inverse:   #FFFFFF;

  /* 背景与边框 */
  --c-bg-page:        #F8FAFF;
  --c-bg-card:        #FFFFFF;
  --c-bg-hover:       #F0F7FF;
  --c-border:         #E2E8F0;
  --c-border-light:   #EDF2F7;

  /* LEVEL 颜色 */
  --level-00: #64748B;
  --level-01: #2563EB;
  --level-02: #7C3AED;
  --level-03: #059669;
  --level-04: #D97706;
  --level-05: #DC2626;
  --level-06: #0891B2;
  --level-07: #EA580C;
  --level-08: #7C3AED;
  --level-99: #475569;

  /* 字体 */
  --font-body:  'Noto Sans SC', 'PingFang SC', 'Microsoft YaHei', sans-serif;
  --font-ui:    'Inter', 'Noto Sans SC', sans-serif;
  --font-mono:  'JetBrains Mono', 'Courier New', monospace;

  /* 字号 */
  --text-xs:   0.75rem;
  --text-sm:   0.85rem;
  --text-base: 1rem;
  --text-lg:   1.125rem;
  --text-xl:   1.25rem;
  --text-2xl:  1.5rem;
  --text-3xl:  1.875rem;
  --text-4xl:  2.25rem;

  /* 圆角 & 阴影 */
  --radius-sm:  6px;
  --radius-md:  10px;
  --radius-lg:  16px;
  --radius-xl:  24px;
  --shadow-sm:  0 1px 3px rgba(0,0,0,0.06), 0 1px 2px rgba(0,0,0,0.04);
  --shadow-md:  0 4px 12px rgba(0,0,0,0.08), 0 2px 4px rgba(0,0,0,0.05);
  --shadow-lg:  0 10px 32px rgba(0,0,0,0.10), 0 4px 8px rgba(0,0,0,0.06);
  --shadow-glow: 0 0 20px rgba(26,95,150,0.15);

  /* 动画 */
  --transition: 0.2s ease;
  --transition-slow: 0.4s ease;

  /* 布局 */
  --max-width-content: 860px;
  --max-width-wide:    1200px;
}

/* ── 2. Reset & Base ─────────────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html {
  scroll-behavior: smooth;
  font-size: 16px;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-body);
  font-size: var(--text-base);
  color: var(--c-text-primary);
  background: var(--c-bg-page);
  line-height: 1.8;
  min-height: 100vh;
}

img, video, svg { max-width: 100%; display: block; }
a { color: var(--c-primary); text-decoration: none; }
a:hover { text-decoration: underline; }

/* ── 3. 顶部固定导航栏（章节页用）──────────────────────────────── */
.top-nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255,255,255,0.92);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--c-border);
  box-shadow: 0 1px 4px rgba(0,0,0,0.05);
}
.top-nav-inner {
  max-width: var(--max-width-content);
  margin: 0 auto;
  padding: 0 2rem;
  height: 52px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}
.nav-home {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  font-weight: 700;
  color: var(--c-primary);
  text-decoration: none;
  white-space: nowrap;
  font-size: var(--text-sm);
  font-family: var(--font-ui);
}
.nav-home:hover { color: var(--c-primary-dark); text-decoration: none; }
.nav-home-icon { font-size: 1.1rem; }
.nav-breadcrumb {
  display: flex;
  align-items: center;
  gap: 0.35rem;
  font-size: var(--text-xs);
  color: var(--c-text-muted);
  overflow: hidden;
  flex: 1;
  min-width: 0;
}
.nav-level { font-weight: 700; color: var(--c-primary); white-space: nowrap; }
.nav-sep   { color: var(--c-border); flex-shrink: 0; }
.nav-chapter, .nav-section {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}
.nav-chapter-jump { display: flex; gap: 0.4rem; white-space: nowrap; }
.nav-prev, .nav-next {
  padding: 0.25rem 0.65rem;
  border: 1px solid var(--c-border);
  border-radius: var(--radius-sm);
  font-size: var(--text-xs);
  color: var(--c-text-secondary);
  text-decoration: none;
  transition: all var(--transition);
  font-family: var(--font-ui);
}
.nav-prev:hover, .nav-next:hover {
  background: var(--c-primary-light);
  border-color: var(--c-primary);
  color: var(--c-primary);
  text-decoration: none;
}
.nav-prev.disabled, .nav-next.disabled { opacity: 0.3; pointer-events: none; }

/* GitHub Star 按钮样式 */
.nav-github-link {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  padding: 0.25rem 0.65rem;
  border-radius: var(--radius-sm);
  background: #24292F;
  color: #FFFFFF !important;
  font-size: var(--text-xs);
  font-weight: 600;
  font-family: var(--font-ui);
  text-decoration: none !important;
  transition: all var(--transition);
  box-shadow: 0 1px 3px rgba(0,0,0,0.12);
  white-space: nowrap;
  flex-shrink: 0;
}
.nav-github-link:hover {
  background: #0969DA;
  color: #FFFFFF !important;
  transform: translateY(-1px);
  box-shadow: 0 3px 8px rgba(9,105,218,0.3);
  text-decoration: none !important;
}
.nav-github-link svg { fill: currentColor; }

/* ── 4. 页面布局容器 ─────────────────────────────────────────────── */
.page-wrapper {
  max-width: var(--max-width-content);
  margin: 0 auto;
  padding: 2.5rem 2rem 4rem;
}

/* ── 5. 章节页眉 ─────────────────────────────────────────────────── */
.chapter-header {
  margin-bottom: 2.5rem;
  padding-bottom: 2rem;
  border-bottom: 2px solid var(--c-border-light);
}
.chapter-meta {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 1rem;
  flex-wrap: wrap;
}
.file-id {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  color: var(--c-text-muted);
  background: var(--c-border-light);
  padding: 0.15rem 0.5rem;
  border-radius: var(--radius-sm);
}
.reading-time, .difficulty {
  font-size: var(--text-sm);
  color: var(--c-text-muted);
}
.chapter-header h1 {
  font-size: var(--text-3xl);
  font-weight: 700;
  color: var(--c-text-primary);
  line-height: 1.3;
  margin-bottom: 0.75rem;
}
.chapter-lead {
  font-size: var(--text-lg);
  color: var(--c-text-secondary);
  line-height: 1.6;
  max-width: 640px;
}

/* ── 6. 学习目标卡 ───────────────────────────────────────────────── */
.learning-goals {
  background: var(--c-primary-light);
  border-left: 4px solid var(--c-primary);
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  padding: 1.25rem 1.5rem;
  margin-bottom: 2rem;
}
.learning-goals h2 {
  font-size: var(--text-base);
  font-weight: 700;
  color: var(--c-primary);
  margin-bottom: 0.75rem;
}
.learning-goals ul { padding-left: 1.25rem; }
.learning-goals li { margin-bottom: 0.35rem; font-size: var(--text-sm); color: var(--c-text-secondary); }

/* ── 7. 场景引入 ─────────────────────────────────────────────────── */
.scene-intro {
  background: linear-gradient(135deg, #F0F7FF, #EEF2FF);
  border-radius: var(--radius-lg);
  padding: 1.75rem 2rem;
  margin-bottom: 2.5rem;
  position: relative;
  overflow: hidden;
}
.scene-intro::before {
  content: '"';
  position: absolute;
  top: -0.5rem; left: 1rem;
  font-size: 5rem;
  color: var(--c-primary);
  opacity: 0.08;
  font-family: Georgia, serif;
  line-height: 1;
}
.scene-intro p { color: var(--c-text-secondary); font-size: var(--text-base); }

/* ── 8. 正文标题体系 ─────────────────────────────────────────────── */
.chapter-content h2 {
  font-size: var(--text-2xl);
  font-weight: 700;
  color: var(--c-text-primary);
  margin: 2.5rem 0 1rem;
  padding-bottom: 0.5rem;
  border-bottom: 2px solid var(--c-border-light);
}
.chapter-content h3 {
  font-size: var(--text-xl);
  font-weight: 600;
  color: var(--c-primary-dark);
  margin: 1.75rem 0 0.75rem;
}
.chapter-content h4 {
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--c-text-secondary);
  margin: 1.25rem 0 0.5rem;
}
.chapter-content p { margin-bottom: 1.1rem; }
.chapter-content ul, .chapter-content ol {
  padding-left: 1.5rem;
  margin-bottom: 1.1rem;
}
.chapter-content li { margin-bottom: 0.4rem; }

/* ── 9. 六种边栏组件（Callout）────────────────────────────────── */
.callout {
  border-radius: var(--radius-md);
  padding: 1.1rem 1.4rem;
  margin: 1.5rem 0;
  border-left: 4px solid;
  position: relative;
}
.callout-label {
  font-size: var(--text-xs);
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin-bottom: 0.5rem;
  display: flex;
  align-items: center;
  gap: 0.35rem;
}
.callout p:last-child { margin-bottom: 0; }

/* Tips 💡 */
.callout-tips {
  background: #FFFBEB;
  border-color: #F59E0B;
}
.callout-tips .callout-label { color: #B45309; }

/* Warning ⚠️ */
.callout-warning {
  background: #FFF1F2;
  border-color: #F43F5E;
}
.callout-warning .callout-label { color: #BE123C; }

/* Case 🏗️ */
.callout-case {
  background: #F0FDF4;
  border-color: #22C55E;
}
.callout-case .callout-label { color: #15803D; }

/* Analogy 🔍 */
.callout-analogy {
  background: #EEF2FF;
  border-color: #818CF8;
}
.callout-analogy .callout-label { color: #4338CA; }

/* Extension 🔭 */
.callout-extension {
  background: #F0F9FF;
  border-color: #38BDF8;
}
.callout-extension .callout-label { color: #0369A1; }

/* Key Concept 📌 */
.key-concept {
  background: var(--c-primary-light);
  border: 1.5px solid var(--c-primary);
  border-radius: var(--radius-md);
  padding: 1.25rem 1.5rem;
  margin: 1.5rem 0;
}
.key-concept h4 {
  color: var(--c-primary) !important;
  font-size: var(--text-sm) !important;
  font-weight: 700 !important;
  margin: 0 0 0.5rem !important;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}
.key-concept p { margin-bottom: 0; font-size: var(--text-sm); }

/* Formula Block & Math Styles */
.formula-block {
  margin: 1rem 0;
  padding: 1rem 1.25rem;
  background: #FFFFFF;
  border: 1px solid var(--c-border);
  border-left: 4px solid var(--c-primary);
  border-radius: var(--radius-sm);
  overflow-x: auto;
  font-family: var(--font-number), var(--font-body);
  font-size: 1rem;
  line-height: 1.6;
}
.formula-main {
  text-align: center;
  font-size: 1.1rem;
  font-weight: 600;
  color: var(--c-primary-dark);
  padding: 0.5rem 0;
}
.formula-param-list {
  margin-top: 0.75rem;
  padding-left: 1.25rem;
  font-size: 0.9rem;
  color: var(--c-text-secondary);
}
.formula-param-list li {
  margin-bottom: 0.35rem;
}

/* ── 10. SVG 图表 ───────────────────────────────────────────────── */
.svg-figure {
  margin: 1.75rem 0;
  background: var(--c-bg-card);
  border: 1px solid var(--c-border);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  overflow-x: auto;
  box-shadow: var(--shadow-sm);
}
.svg-figure figcaption {
  text-align: center;
  font-size: var(--text-sm);
  color: var(--c-text-muted);
  margin-top: 0.75rem;
  font-style: italic;
}

/* ── 11. 数据表格 ───────────────────────────────────────────────── */
.table-wrapper,
.table-container {
  width: 100%;
  overflow-x: auto;
  margin: 1.5rem 0;
  border-radius: var(--radius-md);
}
.data-table {
  width: 100%;
  border-collapse: collapse;
  margin: 0;
  font-size: var(--text-sm);
  background: var(--c-bg-card);
  border-radius: var(--radius-md);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
}
.data-table th {
  background: var(--c-primary);
  color: var(--c-text-inverse);
  font-weight: 600;
  padding: 0.75rem 1rem;
  text-align: left;
  font-size: var(--text-xs);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}
.data-table td {
  padding: 0.65rem 1rem;
  border-bottom: 1px solid var(--c-border-light);
  color: var(--c-text-secondary);
}
.data-table tr:last-child td { border-bottom: none; }
.data-table tr:hover td { background: var(--c-bg-hover); }
.data-table tr:nth-child(even) td { background: #FAFBFF; }
.data-table tr:nth-child(even):hover td { background: var(--c-bg-hover); }

/* ── 12. 本节小结 ───────────────────────────────────────────────── */
.chapter-summary {
  background: var(--c-bg-card);
  border: 1px solid var(--c-border);
  border-radius: var(--radius-lg);
  padding: 1.75rem 2rem;
  margin: 2.5rem 0;
  box-shadow: var(--shadow-sm);
}
.chapter-summary h2 {
  font-size: var(--text-lg) !important;
  border: none !important;
  margin-top: 0 !important;
  color: var(--c-text-primary);
  margin-bottom: 1rem !important;
}
.chapter-summary ul { padding-left: 1.25rem; }
.chapter-summary li { margin-bottom: 0.5rem; font-size: var(--text-sm); }

/* ── 13. 底部章节导航 ───────────────────────────────────────────── */
.bottom-nav {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 0.75rem;
  margin: 2.5rem 0;
  padding-top: 2rem;
  border-top: 1px solid var(--c-border);
}
.bottom-nav-prev, .bottom-nav-next {
  display: flex;
  flex-direction: column;
  gap: 0.3rem;
  padding: 0.9rem 1.1rem;
  border: 1px solid var(--c-border);
  border-radius: var(--radius-md);
  text-decoration: none;
  transition: all var(--transition);
  background: var(--c-bg-card);
}
.bottom-nav-prev { text-align: left; }
.bottom-nav-next { text-align: right; }
.bottom-nav-prev:hover, .bottom-nav-next:hover {
  border-color: var(--c-primary);
  background: var(--c-primary-light);
  text-decoration: none;
  transform: translateY(-1px);
  box-shadow: var(--shadow-sm);
}
.bnav-label { font-size: var(--text-xs); color: var(--c-text-muted); }
.bnav-title { font-size: var(--text-sm); color: var(--c-text-primary); font-weight: 500; }
.bottom-nav-home {
  align-self: center;
  padding: 0.6rem 1rem;
  border: 1px solid var(--c-border);
  border-radius: var(--radius-md);
  text-decoration: none;
  color: var(--c-text-secondary);
  font-size: var(--text-sm);
  text-align: center;
  transition: all var(--transition);
  background: var(--c-bg-card);
  white-space: nowrap;
}
.bottom-nav-home:hover {
  background: var(--c-bg-hover);
  text-decoration: none;
  border-color: var(--c-text-muted);
}

/* ── 14. 知识测验 ───────────────────────────────────────────────── */
.quiz-section,
.chapter-quiz {
  background: var(--c-bg-card);
  border: 1px solid var(--c-border);
  border-radius: var(--radius-xl);
  padding: 2rem 2.25rem;
  margin: 2.5rem 0;
  box-shadow: var(--shadow-md);
}
.quiz-section > h2,
.chapter-quiz > h2 {
  font-size: var(--text-xl) !important;
  border: none !important;
  margin-top: 0 !important;
  margin-bottom: 1.75rem !important;
  color: var(--c-text-primary);
}
.quiz-question {
  margin-bottom: 1.75rem;
  padding-bottom: 1.75rem;
  border-bottom: 1px solid var(--c-border-light);
}
.quiz-question:last-child { border-bottom: none; margin-bottom: 0; padding-bottom: 0; }
.question-text {
  margin-bottom: 0.9rem;
  font-weight: 500;
  line-height: 1.6;
}
.quiz-options { display: flex; flex-direction: column; gap: 0.5rem; }
.quiz-option {
  display: flex;
  align-items: flex-start;
  gap: 0.6rem;
  padding: 0.6rem 0.9rem;
  border: 1px solid var(--c-border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all var(--transition);
  font-size: var(--text-sm);
  line-height: 1.5;
}
.quiz-option:hover { background: var(--c-primary-light); border-color: var(--c-primary); }
.quiz-option input[type="radio"] { margin-top: 0.1rem; flex-shrink: 0; accent-color: var(--c-primary); }
.quiz-btn,
.btn-check-answer {
  margin-top: 1rem;
  padding: 0.55rem 1.4rem;
  background: var(--c-primary);
  color: white;
  border: none;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: var(--text-sm);
  font-family: var(--font-body);
  font-weight: 600;
  transition: background var(--transition);
}
.quiz-btn:hover,
.btn-check-answer:hover { background: var(--c-primary-dark); }
.quiz-answer {
  margin-top: 1rem;
  padding: 1rem 1.1rem;
  background: #F0FDF4;
  border: 1px solid #BBF7D0;
  border-radius: var(--radius-sm);
  font-size: var(--text-sm);
  line-height: 1.7;
}
.quiz-answer p { margin-bottom: 0.35rem; }
.quiz-answer p:last-child { margin-bottom: 0; }
.quiz-score {
  text-align: center;
  padding: 1.25rem;
  background: var(--c-primary-light);
  border-radius: var(--radius-md);
  font-weight: 600;
  color: var(--c-primary);
  margin-top: 1rem;
  display: none;
}

/* ── 15. 相关章节 ───────────────────────────────────────────────── */
.cross-refs,
.related-chapters {
  margin: 3rem 0 2rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--c-border-light);
}
.cross-refs h2,
.related-chapters h2 {
  font-size: var(--text-lg) !important;
  border: none !important;
  margin-top: 0 !important;
  margin-bottom: 1.25rem !important;
  color: var(--c-text-primary);
}
.cross-ref-list,
.related-chapters ul,
.cross-refs ul {
  display: flex;
  flex-wrap: wrap;
  gap: 0.65rem;
  list-style: none;
  padding: 0;
}
.cross-ref-list li a,
.related-chapters ul li a,
.cross-refs ul li a {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  padding: 0.45rem 0.95rem;
  border: 1px solid var(--c-primary);
  border-radius: 20px;
  font-size: var(--text-sm);
  color: var(--c-primary);
  background: var(--c-bg-card);
  transition: all var(--transition);
}
.cross-ref-list li a:hover,
.related-chapters ul li a:hover,
.cross-refs ul li a:hover {
  background: var(--c-primary);
  color: white;
  text-decoration: none;
  box-shadow: var(--shadow-sm);
}

/* ── 16. 页脚 ───────────────────────────────────────────────────── */
.chapter-footer {
  margin-top: 3rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--c-border-light);
  text-align: center;
  font-size: var(--text-xs);
  color: var(--c-text-muted);
}

/* ── 17. 返回顶端按钮 ───────────────────────────────────────────── */
.btn-back-top {
  position: fixed;
  bottom: 2.2rem;
  right: 2.2rem;
  width: 46px;
  height: 46px;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--c-primary, #1A5F96) 0%, #0F4570 100%);
  color: #FFFFFF;
  border: 1px solid rgba(255, 255, 255, 0.25);
  cursor: pointer;
  box-shadow: 0 4px 16px rgba(26, 95, 150, 0.35), 0 2px 6px rgba(0, 0, 0, 0.15);
  opacity: 0;
  pointer-events: none;
  transform: translateY(14px) scale(0.92);
  transition: opacity 0.3s ease, transform 0.3s cubic-bezier(0.34, 1.56, 0.64, 1), background 0.3s ease, box-shadow 0.3s ease;
  z-index: 999;
  display: flex;
  align-items: center;
  justify-content: center;
  outline: none;
  -webkit-tap-highlight-color: transparent;
}
.btn-back-top svg {
  width: 20px;
  height: 20px;
  stroke: currentColor;
  transition: transform 0.25s ease;
  flex-shrink: 0;
}
.btn-back-top.visible {
  opacity: 1;
  pointer-events: auto;
  transform: translateY(0) scale(1);
}
.btn-back-top:hover {
  background: linear-gradient(135deg, #1D6FB0 0%, #0D3B61 100%);
  box-shadow: 0 8px 24px rgba(26, 95, 150, 0.5), 0 4px 10px rgba(0, 0, 0, 0.2);
  transform: translateY(-4px) scale(1.06) !important;
}
.btn-back-top:hover svg {
  transform: translateY(-2px);
}
.btn-back-top:active {
  transform: translateY(-1px) scale(0.96) !important;
  box-shadow: 0 2px 8px rgba(26, 95, 150, 0.35);
}


/* ── 18. 代码块 ─────────────────────────────────────────────────── */
code {
  font-family: var(--font-mono);
  font-size: 0.88em;
  background: var(--c-border-light);
  color: var(--c-primary-dark);
  padding: 0.1em 0.35em;
  border-radius: 3px;
}
pre {
  background: #1E293B;
  color: #E2E8F0;
  border-radius: var(--radius-md);
  padding: 1.25rem 1.5rem;
  overflow-x: auto;
  margin: 1.5rem 0;
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  line-height: 1.7;
}
pre code { background: none; color: inherit; padding: 0; }

/* ── 19. 响应式 ─────────────────────────────────────────────────── */
@media (max-width: 768px) {
  .page-wrapper { padding: 1.5rem 1rem 3rem; }
  .top-nav-inner { padding: 0 1rem; }
  .chapter-header h1 { font-size: var(--text-2xl); }
  .bottom-nav { grid-template-columns: 1fr 1fr; }
  .bottom-nav-home { grid-column: 1 / -1; order: -1; }
  .nav-breadcrumb .nav-chapter, .nav-breadcrumb .nav-section { display: none; }
  .quiz-section { padding: 1.25rem 1.25rem; }
}
@media (max-width: 480px) {
  .chapter-meta { gap: 0.5rem; }
  .nav-chapter-jump { display: none; }
  .bottom-nav { grid-template-columns: 1fr; }
  .bottom-nav-home { order: 0; }
}

/* ── 20. 难度标签颜色覆盖 ───────────────────────────────────────── */
.diff-beginner  { color: #059669; }
.diff-medium    { color: #D97706; }
.diff-advanced  { color: #DC2626; }

/* ── 21. 工具类 ─────────────────────────────────────────────────── */
.text-center { text-align: center; }
.text-muted  { color: var(--c-text-muted); }
.mt-1 { margin-top: 0.5rem; }
.mt-2 { margin-top: 1rem; }
.mt-3 { margin-top: 1.5rem; }
.mb-1 { margin-bottom: 0.5rem; }
.mb-2 { margin-bottom: 1rem; }
.highlight { background: #FEF9C3; padding: 0.1em 0.3em; border-radius: 3px; }

/* ── 22. PWA 渐进式应用与安装兼容 UI 样式 ────────────────────────────── */

/* PWA 导航栏/ Header 按钮 */
.pwa-install-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.38rem 0.85rem;
  background: linear-gradient(135deg, var(--c-primary), var(--c-primary-dark));
  color: #FFFFFF !important;
  font-size: var(--text-xs);
  font-weight: 600;
  font-family: var(--font-ui);
  border-radius: 30px;
  border: 1px solid rgba(255, 255, 255, 0.2);
  box-shadow: 0 2px 8px rgba(26, 95, 150, 0.25);
  cursor: pointer;
  transition: all var(--transition);
  white-space: nowrap;
  user-select: none;
}

.pwa-install-btn:hover {
  background: linear-gradient(135deg, #1D6FB0, #0B345C);
  box-shadow: 0 4px 14px rgba(26, 95, 150, 0.4);
  transform: translateY(-1px);
  text-decoration: none !important;
}

.pwa-install-btn .pwa-btn-icon {
  font-size: 0.95rem;
  line-height: 1;
}

.pwa-btn-pulse {
  animation: pwaPulse 2.5s infinite;
}

@keyframes pwaPulse {
  0% { box-shadow: 0 0 0 0 rgba(26, 95, 150, 0.5); }
  70% { box-shadow: 0 0 0 8px rgba(26, 95, 150, 0); }
  100% { box-shadow: 0 0 0 0 rgba(26, 95, 150, 0); }
}

/* PWA 模态框 (iOS 步骤引导 & 通用提示) */
.pwa-modal-overlay {
  position: fixed;
  top: 0;
  left: 0;
  width: 100vw;
  height: 100vh;
  background: rgba(15, 23, 42, 0.6);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  z-index: 9999;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 1.5rem;
  opacity: 0;
  transition: opacity 0.3s ease;
}

.pwa-modal-overlay.pwa-modal-active {
  opacity: 1;
}

.pwa-modal-card {
  background: #FFFFFF;
  border-radius: var(--radius-xl);
  max-width: 440px;
  width: 100%;
  padding: 1.75rem;
  box-shadow: 0 20px 50px rgba(0, 0, 0, 0.22);
  border: 1px solid rgba(255, 255, 255, 0.8);
  transform: translateY(20px) scale(0.96);
  transition: transform 0.3s cubic-bezier(0.16, 1, 0.3, 1);
}

.pwa-modal-overlay.pwa-modal-active .pwa-modal-card {
  transform: translateY(0) scale(1);
}

.pwa-modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 1rem;
}

.pwa-modal-title {
  display: flex;
  align-items: center;
  gap: 0.6rem;
}

.pwa-modal-title h3 {
  font-size: var(--text-lg);
  font-weight: 700;
  color: var(--c-text-primary);
  margin: 0;
}

.pwa-icon-logo {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  background: var(--c-primary-light);
  color: var(--c-primary);
  border-radius: 10px;
  font-size: 1.2rem;
}

.pwa-modal-close-btn {
  background: none;
  border: none;
  font-size: 1.5rem;
  color: var(--c-text-muted);
  cursor: pointer;
  padding: 0.2rem;
  line-height: 1;
  border-radius: 50%;
  transition: color var(--transition);
}

.pwa-modal-close-btn:hover {
  color: var(--c-text-primary);
}

.pwa-modal-subtitle {
  font-size: var(--text-sm);
  color: var(--c-text-secondary);
  line-height: 1.6;
  margin-bottom: 1.25rem;
}

.pwa-ios-steps {
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
  background: var(--c-bg-page);
  padding: 1rem 1.25rem;
  border-radius: var(--radius-lg);
  border: 1px solid var(--c-border);
}

.pwa-step-item {
  display: flex;
  align-items: center;
  gap: 0.85rem;
  font-size: var(--text-sm);
  color: var(--c-text-primary);
}

.pwa-step-num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 24px;
  height: 24px;
  background: var(--c-primary);
  color: #FFFFFF;
  border-radius: 50%;
  font-size: 0.75rem;
  font-weight: 700;
  flex-shrink: 0;
}

.pwa-step-text {
  line-height: 1.5;
}

.pwa-inline-icon {
  display: inline-block;
  background: #E2E8F0;
  padding: 0.1rem 0.4rem;
  border-radius: 4px;
  font-size: 0.9rem;
}

.pwa-modal-footer {
  display: flex;
  align-items: center;
  justify-content: flex-end;
  gap: 0.75rem;
  margin-top: 1.5rem;
}

.pwa-btn {
  padding: 0.5rem 1.1rem;
  border-radius: var(--radius-md);
  font-size: var(--text-sm);
  font-weight: 600;
  font-family: var(--font-ui);
  cursor: pointer;
  border: none;
  transition: all var(--transition);
}

.pwa-btn-primary {
  background: var(--c-primary);
  color: #FFFFFF;
}

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

.pwa-btn-secondary {
  background: var(--c-border-light);
  color: var(--c-text-secondary);
}

.pwa-btn-secondary:hover {
  background: var(--c-border);
  color: var(--c-text-primary);
}

/* PWA Toast 提示组件 */
.pwa-toast-container {
  position: fixed;
  bottom: 2rem;
  left: 50%;
  transform: translateX(-50%);
  z-index: 10000;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  pointer-events: none;
  width: max-content;
  max-width: 90vw;
}

.pwa-toast {
  background: rgba(15, 23, 42, 0.9);
  color: #FFFFFF;
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  padding: 0.7rem 1.2rem;
  border-radius: 30px;
  font-size: var(--text-xs);
  font-weight: 500;
  font-family: var(--font-ui);
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.2);
  opacity: 0;
  transform: translateY(12px);
  transition: opacity 0.3s ease, transform 0.3s ease;
  pointer-events: auto;
  text-align: center;
}

.pwa-toast.pwa-toast-show {
  opacity: 1;
  transform: translateY(0);
}

.pwa-toast-success { border-left: 4px solid #10B981; }
.pwa-toast-warning { border-left: 4px solid #F59E0B; }
.pwa-toast-info    { border-left: 4px solid #3B82F6; }

/* 独立应用模式下 UI 微调 */
@media (display-mode: standalone) {
  .site-header, .top-nav {
    padding-top: env(safe-area-inset-top);
  }
}