/* ============================================================
   Learning Hub — Design System
   学者书斋风格：暖纸色底、深青+暖金、衬线标题、宽裕留白
   ============================================================ */

:root {
  /* 配色 */
  --bg: #faf7f2;
  --bg-soft: #f3ede3;
  --bg-card: #ffffff;
  --ink: #2b2b2b;
  --ink-soft: #555;
  --muted: #8a8580;
  --rule: #e5dfd4;
  --rule-soft: #f0ebe2;
  --accent: #2d6a6a;
  --accent-hover: #245757;
  --accent-soft: rgba(45, 106, 106, 0.08);
  --gold: #b8893a;
  --gold-soft: rgba(184, 137, 58, 0.1);
  --danger: #c0392b;
  --success: #27ae60;
  --warn: #e67e22;

  /* 字体 */
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Helvetica Neue", Arial, sans-serif;
  --serif: "Noto Serif SC", "Songti SC", "Source Han Serif SC", "Georgia", serif;
  --mono: "SF Mono", "Fira Code", "Consolas", monospace;

  /* 间距 */
  --radius: 12px;
  --radius-sm: 8px;
  --radius-lg: 20px;

  /* 阴影 */
  --shadow-sm: 0 1px 3px rgba(43, 40, 37, 0.06);
  --shadow: 0 4px 16px rgba(43, 40, 37, 0.08);
  --shadow-lg: 0 12px 40px rgba(43, 40, 37, 0.12);

  /* 布局 */
  --nav-h: 60px;
  --max-w: 1080px;
  --dock-h: 56px;
}

* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }

body {
  background: var(--bg);
  color: var(--ink);
  font-family: var(--sans);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  padding-top: var(--nav-h);
  padding-bottom: env(safe-area-inset-bottom);
}

/* ============================================================
   顶部导航
   ============================================================ */
.nav {
  position: fixed;
  top: 0; left: 0; right: 0;
  height: var(--nav-h);
  background: rgba(250, 247, 242, 0.92);
  backdrop-filter: blur(20px) saturate(160%);
  -webkit-backdrop-filter: blur(20px) saturate(160%);
  border-bottom: 1px solid var(--rule);
  z-index: 1000;
  display: flex;
  align-items: center;
  padding: 0 20px;
  transition: box-shadow 0.3s;
}
.nav.scrolled { box-shadow: var(--shadow-sm); }

.nav-inner {
  max-width: var(--max-w);
  width: 100%;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.nav-brand {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  color: var(--ink);
  cursor: pointer;
  flex-shrink: 0;
}
.nav-brand-mark {
  width: 32px; height: 32px;
  border-radius: 8px;
  background: var(--accent);
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--serif);
  font-size: 18px;
  font-weight: 700;
}
.nav-brand-text {
  font-family: var(--serif);
  font-size: 17px;
  font-weight: 700;
  letter-spacing: 0.5px;
}

.nav-tabs {
  display: flex;
  align-items: center;
  gap: 2px;
}
.nav-tab {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 8px 16px;
  border: none;
  background: transparent;
  color: var(--muted);
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  border-radius: var(--radius-sm);
  transition: all 0.2s;
  white-space: nowrap;
}
.nav-tab:hover { background: var(--accent-soft); color: var(--accent); }
.nav-tab.active { background: var(--accent); color: #fff; }
.nav-tab-icon { font-size: 16px; }

/* 移动端汉堡 */
.nav-mobile-toggle {
  display: none;
  background: none;
  border: none;
  font-size: 22px;
  color: var(--ink);
  cursor: pointer;
  padding: 4px 8px;
}

/* ============================================================
   主容器
   ============================================================ */
#app {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 24px 20px calc(var(--dock-h) + 40px);
}

.view { display: none; animation: fadeIn 0.25s ease; }
.view.active { display: block; }

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(6px); }
  to { opacity: 1; transform: translateY(0); }
}

/* ============================================================
   首页 Hero
   ============================================================ */
.hero {
  text-align: center;
  padding: 40px 20px 32px;
}
.hero-eyebrow {
  display: inline-block;
  font-size: 12px;
  letter-spacing: 3px;
  color: var(--accent);
  text-transform: uppercase;
  font-weight: 700;
  margin-bottom: 14px;
}
.hero h1 {
  font-family: var(--serif);
  font-size: clamp(28px, 5vw, 40px);
  font-weight: 800;
  line-height: 1.2;
  letter-spacing: -1px;
  margin-bottom: 12px;
}
.hero h1 .ac { color: var(--accent); }
.hero h1 .gold { color: var(--gold); }
.hero-lead {
  color: var(--muted);
  font-size: 15px;
  max-width: 560px;
  margin: 0 auto;
}

/* 统计卡片 */
.hero-stats {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
  margin-top: 32px;
}
.hero-stat {
  background: var(--bg-card);
  border: 1px solid var(--rule);
  border-radius: var(--radius);
  padding: 20px 12px;
  text-align: center;
  transition: transform 0.2s, box-shadow 0.2s;
}
.hero-stat:hover { transform: translateY(-2px); box-shadow: var(--shadow); }
.hero-stat-num {
  font-family: var(--serif);
  font-size: 28px;
  font-weight: 800;
  color: var(--accent);
  letter-spacing: -0.5px;
}
.hero-stat-num.gold { color: var(--gold); }
.hero-stat-label {
  font-size: 12px;
  color: var(--muted);
  margin-top: 4px;
}

/* 快捷入口 */
.section-title {
  font-family: var(--serif);
  font-size: 20px;
  font-weight: 700;
  margin: 36px 0 16px;
  padding-bottom: 10px;
  border-bottom: 2px solid var(--rule);
  display: flex;
  align-items: center;
  gap: 8px;
}
.section-title .dot {
  width: 6px; height: 6px;
  border-radius: 50%;
  background: var(--accent);
}

.quick-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 14px;
}
.quick-card {
  background: var(--bg-card);
  border: 1px solid var(--rule);
  border-radius: var(--radius);
  padding: 20px 16px;
  cursor: pointer;
  transition: all 0.2s;
  text-decoration: none;
  color: var(--ink);
  display: flex;
  flex-direction: column;
  gap: 8px;
}
.quick-card:hover {
  border-color: var(--accent);
  transform: translateY(-2px);
  box-shadow: var(--shadow);
}
.quick-card-icon {
  font-size: 28px;
  line-height: 1;
}
.quick-card-title {
  font-weight: 700;
  font-size: 15px;
}
.quick-card-desc {
  font-size: 12px;
  color: var(--muted);
}

/* ============================================================
   课程列表
   ============================================================ */
.filter-bar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  margin-bottom: 20px;
}
.filter-btn {
  padding: 6px 16px;
  border: 1px solid var(--rule);
  border-radius: 999px;
  background: var(--bg-card);
  color: var(--muted);
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s;
}
.filter-btn:hover { border-color: var(--accent); color: var(--accent); }
.filter-btn.active { background: var(--accent); color: #fff; border-color: var(--accent); }

.search-input {
  flex: 1;
  min-width: 180px;
  padding: 8px 14px;
  border: 1px solid var(--rule);
  border-radius: var(--radius-sm);
  font-size: 14px;
  font-family: inherit;
  background: var(--bg-card);
  color: var(--ink);
  outline: none;
  transition: border-color 0.2s;
}
.search-input:focus { border-color: var(--accent); }

.course-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 20px;
}

.course-card {
  background: var(--bg-card);
  border: 1px solid var(--rule);
  border-radius: var(--radius-lg);
  overflow: hidden;
  cursor: pointer;
  transition: all 0.3s;
  display: flex;
  flex-direction: column;
}
.course-card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-lg);
  border-color: var(--accent);
}

.course-cover {
  height: 80px;
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  overflow: hidden;
}
.course-cover-bg {
  position: absolute;
  inset: 0;
  background: linear-gradient(135deg, var(--c1, var(--accent)), var(--c2, var(--accent)));
}
.course-cover-icon {
  position: relative;
  z-index: 1;
  color: rgba(255,255,255,0.9);
  font-size: 24px;
  font-weight: 700;
  font-family: var(--mono);
}
.course-cover-tag {
  position: absolute;
  top: 8px; right: 8px;
  z-index: 1;
  background: rgba(255,255,255,0.25);
  color: #fff;
  font-size: 11px;
  font-weight: 600;
  padding: 3px 10px;
  border-radius: 999px;
  backdrop-filter: blur(4px);
}

.course-body { padding: 16px; flex: 1; display: flex; flex-direction: column; }
.course-body h3 { font-size: 16px; font-weight: 700; margin-bottom: 4px; }
.course-source { font-size: 12px; color: var(--muted); margin-bottom: 12px; }
.course-meta {
  display: flex;
  gap: 16px;
  font-size: 13px;
  color: var(--ink-soft);
  margin-bottom: 12px;
}
.course-meta-item { display: flex; align-items: center; gap: 4px; }
.course-chapters {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-bottom: 12px;
}
.course-chapter-tag {
  font-size: 11px;
  padding: 3px 8px;
  border-radius: 4px;
  background: var(--bg-soft);
  color: var(--muted);
}
.course-actions {
  margin-top: auto;
  display: flex;
  gap: 8px;
}
.course-btn {
  flex: 1;
  padding: 8px 12px;
  border: 1px solid var(--rule);
  border-radius: var(--radius-sm);
  background: var(--bg-card);
  color: var(--ink);
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  text-align: center;
  transition: all 0.2s;
  text-decoration: none;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 4px;
}
.course-btn:hover { border-color: var(--accent); color: var(--accent); }
.course-btn.primary { background: var(--accent); color: #fff; border-color: var(--accent); }
.course-btn.primary:hover { background: var(--accent-hover); }

/* ============================================================
   课程详情页（iframe）
   ============================================================ */
.course-detail {
  position: fixed;
  top: var(--nav-h);
  left: 0; right: 0; bottom: 0;
  background: var(--bg);
  z-index: 999;
  display: none;
  flex-direction: column;
}
.course-detail.active { display: flex; }

.course-detail-bar {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 10px 20px;
  background: var(--bg-card);
  border-bottom: 1px solid var(--rule);
  flex-shrink: 0;
}
.back-btn {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 6px 14px;
  border: 1px solid var(--rule);
  border-radius: var(--radius-sm);
  background: var(--bg-card);
  color: var(--ink);
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s;
}
.back-btn:hover { border-color: var(--accent); color: var(--accent); }
.course-detail-title {
  font-family: var(--serif);
  font-size: 16px;
  font-weight: 700;
  flex: 1;
}
.course-detail-quiz-btn {
  padding: 6px 16px;
  background: var(--accent);
  color: #fff;
  border: none;
  border-radius: var(--radius-sm);
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.2s;
}
.course-detail-quiz-btn:hover { background: var(--accent-hover); }

.course-iframe-wrap {
  flex: 1;
  position: relative;
  overflow: hidden;
}
.course-iframe {
  width: 100%;
  height: 100%;
  border: none;
}

/* ============================================================
   做题中心
   ============================================================ */
.quiz-center { max-width: 760px; margin: 0 auto; }

.quiz-modes {
  display: flex;
  gap: 8px;
  margin-bottom: 24px;
}
.quiz-mode-btn {
  flex: 1;
  padding: 10px;
  border: 1px solid var(--rule);
  border-radius: var(--radius);
  background: var(--bg-card);
  color: var(--muted);
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s;
}
.quiz-mode-btn.active { background: var(--accent); color: #fff; border-color: var(--accent); }

.quiz-course-list { display: flex; flex-direction: column; gap: 10px; }
.quiz-course-item {
  background: var(--bg-card);
  border: 1px solid var(--rule);
  border-radius: var(--radius);
  padding: 16px;
  cursor: pointer;
  transition: all 0.2s;
}
.quiz-course-item:hover { border-color: var(--accent); box-shadow: var(--shadow-sm); }
.quiz-course-item.selected { border-color: var(--accent); background: var(--accent-soft); }
.quiz-course-item-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
}
.quiz-course-item-title { font-weight: 700; font-size: 15px; }
.quiz-course-item-meta { font-size: 12px; color: var(--muted); }

.quiz-lesson-list {
  margin-top: 16px;
  display: flex;
  flex-direction: column;
  gap: 8px;
  max-height: 500px;
  overflow-y: auto;
}
.quiz-lesson-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 10px 14px;
  background: var(--bg-card);
  border: 1px solid var(--rule);
  border-radius: var(--radius-sm);
  transition: all 0.2s;
}
.quiz-lesson-item:hover { border-color: var(--accent); }
.quiz-lesson-item-title { font-size: 14px; font-weight: 500; }
.quiz-lesson-item-meta { font-size: 12px; color: var(--muted); }
.quiz-start-btn {
  padding: 6px 16px;
  background: var(--accent);
  color: #fff;
  border: none;
  border-radius: var(--radius-sm);
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  white-space: nowrap;
}
.quiz-start-btn:hover { background: var(--accent-hover); }

.quiz-stats-row {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
  margin-top: 28px;
}
.quiz-stat {
  background: var(--bg-card);
  border: 1px solid var(--rule);
  border-radius: var(--radius);
  padding: 16px;
  text-align: center;
}
.quiz-stat-icon { font-size: 22px; margin-bottom: 6px; }
.quiz-stat-value { font-family: var(--serif); font-size: 22px; font-weight: 800; color: var(--accent); }
.quiz-stat-label { font-size: 12px; color: var(--muted); margin-top: 2px; }

/* ============================================================
   分析中心
   ============================================================ */
.analytics-tabs {
  display: flex;
  gap: 4px;
  margin-bottom: 24px;
  border-bottom: 2px solid var(--rule);
  padding-bottom: 0;
}
.analytics-tab {
  padding: 10px 20px;
  border: none;
  background: transparent;
  color: var(--muted);
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  border-bottom: 3px solid transparent;
  margin-bottom: -2px;
  transition: all 0.2s;
}
.analytics-tab:hover { color: var(--accent); }
.analytics-tab.active { color: var(--accent); border-bottom-color: var(--accent); }

.analytics-panel { display: none; }
.analytics-panel.active { display: block; animation: fadeIn 0.25s ease; }

.viz-chart-box {
  width: 100%;
  height: 420px;
  background: var(--bg-card);
  border: 1px solid var(--rule);
  border-radius: var(--radius);
  margin-bottom: 20px;
}

.viz-section { margin-bottom: 28px; }
.viz-section h3 {
  font-family: var(--serif);
  font-size: 16px;
  font-weight: 700;
  margin-bottom: 12px;
}

/* ============================================================
   工具视图
   ============================================================ */
.tools-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 20px;
}
.tool-card {
  background: var(--bg-card);
  border: 1px solid var(--rule);
  border-radius: var(--radius-lg);
  padding: 24px;
}
.tool-card h3 {
  font-family: var(--serif);
  font-size: 17px;
  font-weight: 700;
  margin-bottom: 12px;
}
.tool-card p { color: var(--muted); font-size: 14px; margin-bottom: 16px; }

/* ============================================================
   底部 Dock
   ============================================================ */
.dock {
  position: fixed;
  bottom: 0; left: 0; right: 0;
  height: var(--dock-h);
  background: rgba(250, 247, 242, 0.95);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-top: 1px solid var(--rule);
  z-index: 900;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0;
  padding: 0 12px env(safe-area-inset-bottom);
}
.dock-item {
  display: flex;
  align-items: center;
  gap: 4px;
  padding: 8px 18px;
  border: none;
  background: transparent;
  color: var(--muted);
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  border-radius: var(--radius-sm);
  transition: all 0.2s;
  white-space: nowrap;
}
.dock-item:hover { background: var(--accent-soft); color: var(--accent); }
.dock-item.active { color: var(--accent); }
.dock-divider {
  width: 1px;
  height: 24px;
  background: var(--rule);
  margin: 0 6px;
}
.dock-time {
  font-family: var(--mono);
  font-size: 13px;
  color: var(--ink);
}
.dock-streak {
  background: var(--gold-soft);
  color: var(--gold);
  font-weight: 800;
  padding: 2px 8px;
  border-radius: 999px;
  font-size: 12px;
}

/* ============================================================
   弹窗/模态
   ============================================================ */
.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(43, 40, 37, 0.4);
  backdrop-filter: blur(4px);
  z-index: 2000;
  display: none;
  align-items: center;
  justify-content: center;
  padding: 20px;
}
.modal-overlay.active { display: flex; animation: fadeIn 0.2s ease; }
.modal {
  background: var(--bg);
  border-radius: var(--radius-lg);
  max-width: 680px;
  width: 100%;
  max-height: 85vh;
  overflow-y: auto;
  box-shadow: var(--shadow-lg);
}
.modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 20px 24px;
  border-bottom: 1px solid var(--rule);
  position: sticky;
  top: 0;
  background: var(--bg);
  border-radius: var(--radius-lg) var(--radius-lg) 0 0;
  z-index: 1;
}
.modal-header h2 {
  font-family: var(--serif);
  font-size: 18px;
  font-weight: 700;
}
.modal-close {
  width: 32px; height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  border: none;
  background: var(--bg-soft);
  border-radius: 50%;
  font-size: 18px;
  cursor: pointer;
  color: var(--muted);
  transition: all 0.2s;
}
.modal-close:hover { background: var(--danger); color: #fff; }
.modal-body { padding: 24px; }

/* ============================================================
   响应式
   ============================================================ */

/* 平板 */
@media (max-width: 1024px) {
  .hero-stats { grid-template-columns: repeat(2, 1fr); }
  .quick-grid { grid-template-columns: repeat(2, 1fr); }
  .quiz-stats-row { grid-template-columns: repeat(2, 1fr); }
  .tools-grid { grid-template-columns: 1fr; }
}

/* 手机 */
@media (max-width: 640px) {
  :root { --nav-h: 54px; }

  .nav-inner { padding: 0; gap: 8px; }
  .nav-tabs {
    display: none;
    position: absolute;
    top: var(--nav-h);
    left: 0; right: 0;
    background: var(--bg);
    border-bottom: 1px solid var(--rule);
    flex-direction: column;
    padding: 8px;
    gap: 4px;
    box-shadow: var(--shadow);
  }
  .nav-tabs.open { display: flex; }
  .nav-tab { width: 100%; justify-content: flex-start; padding: 12px 16px; }
  .nav-mobile-toggle { display: block; }
  .nav-brand-text { font-size: 15px; }

  #app { padding: 16px 14px calc(var(--dock-h) + 32px); }

  .hero { padding: 24px 8px 20px; }
  .hero h1 { font-size: 26px; }
  .hero-stats { grid-template-columns: repeat(2, 1fr); gap: 8px; }
  .hero-stat { padding: 14px 8px; }
  .hero-stat-num { font-size: 22px; }

  .quick-grid { grid-template-columns: repeat(2, 1fr); gap: 10px; }
  .quick-card { padding: 16px 12px; }
  .quick-card-icon { font-size: 24px; }
  .quick-card-title { font-size: 14px; }
  .quick-card-desc { font-size: 11px; }

  .course-grid { grid-template-columns: 1fr; gap: 14px; }

  .quiz-stats-row { grid-template-columns: repeat(2, 1fr); }

  .dock { gap: 0; padding: 0 8px env(safe-area-inset-bottom); }
  .dock-item { padding: 6px 10px; font-size: 12px; }
  .dock-item .btn-label { display: none; }
  .dock-time { font-size: 12px; }
  .dock-divider { margin: 0 2px; }

  .section-title { font-size: 18px; }
  .viz-chart-box { height: 320px; }
  .analytics-tab { padding: 8px 12px; font-size: 13px; }
}

/* 小屏手机 */
@media (max-width: 400px) {
  .hero-stats { grid-template-columns: 1fr 1fr; }
  .quick-grid { grid-template-columns: 1fr; }
}

/* 大屏 */
@media (min-width: 1440px) {
  :root { --max-w: 1200px; }
}

/* 打印 */
@media print {
  .nav, .dock, .modal-overlay { display: none !important; }
  body { padding: 0; }
}

/* 空状态 */
.empty-state {
  text-align: center;
  padding: 48px 20px;
  color: var(--muted);
}
.empty-state-icon { font-size: 48px; margin-bottom: 16px; opacity: 0.5; }
.empty-state h3 { font-size: 16px; color: var(--ink-soft); margin-bottom: 8px; }
.empty-state p { font-size: 14px; }