/* ========================================
   非线性偏微分方程的动力学结构与分析方法讲习班
   主样式表 - 明亮现代风格
   ======================================== */

/* === CSS Variables === */
:root {
  /* 明亮背景 */
  --bg-primary: #f8f9fb;
  --bg-secondary: #f0f2f6;
  --bg-card: #ffffff;
  --bg-card-hover: #f5f7fa;
  --bg-nav: rgba(255, 255, 255, 0.94);
  
  /* 强调色 - 科技蓝 */
  --gold: #1a73e8;
  --gold-light: #4a9af5;
  --gold-dark: #1557b0;
  --gold-glow: rgba(26, 115, 232, 0.12);
  
  /* 辅助色 */
  --blue-accent: #1a73e8;
  --blue-dark: #1557b0;
  --teal: #0d9488;
  --purple: #7c3aed;
  --accent-red: #c41230;
  
  /* 文字 */
  --text-primary: #1a1a2e;
  --text-secondary: #4a4a6a;
  --text-muted: #8888a8;
  --text-heading: #0f0f23;
  
  /* 边框和分割线 */
  --border: rgba(26, 115, 232, 0.12);
  --border-light: rgba(0, 0, 0, 0.06);
  
  /* 阴影 */
  --shadow-sm: 0 1px 4px rgba(0, 0, 0, 0.06);
  --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.08);
  --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.1);
  --shadow-gold: 0 0 0 3px var(--gold-glow);
  
  /* 尺寸 */
  --nav-height: 72px;
  --max-width: 1400px;
  --border-radius: 8px;
  --border-radius-lg: 14px;
  
  /* 字体 */
  --font-math: 'Georgia', 'Times New Roman', serif;
  --font-body: 'Segoe UI', 'PingFang SC', 'Microsoft YaHei', sans-serif;
  --font-code: 'Consolas', 'Fira Code', monospace;
  
  /* 过渡 */
  --transition-fast: 0.2s cubic-bezier(0.4, 0, 0.2, 1);
  --transition: 0.35s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: 0.5s cubic-bezier(0.4, 0, 0.2, 1);
}

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

html {
  scroll-behavior: smooth;
  scroll-padding-top: var(--nav-height);
}

body {
  font-family: var(--font-body);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.75;
  min-height: 100vh;
  overflow-x: hidden;
  overflow-y: scroll; /* 始终显示滚动条，避免内容变化时布局跳动 */
  display: flex;
  flex-direction: column;
}

nav.nav { flex-shrink: 0; }
.hero { flex: 1; display: flex; align-items: center; justify-content: center; }
.page-header { flex-shrink: 0; }
.page-layout { flex: 1; }
.footer { flex-shrink: 0; }

/* === Math Particle Background === */
#math-bg {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: 0;
  pointer-events: none;
  opacity: 0.15;
}

/* === Top Bar === */
.topbar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  background: #003087;
  color: #ffffff;
  height: 120px;
  display: flex;
  align-items: center;
  z-index: 101;
  border-bottom: 2px solid var(--gold);
  box-shadow: 0 2px 12px rgba(0, 0, 0, 0.18);
}
.topbar-inner {
  max-width: var(--max-width);
  width: 100%;
  margin: 0 auto;
  padding: 0 28px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
}
.topbar-side {
  display: flex;
  align-items: center;
  gap: 14px;
  flex: 0 0 auto;
}
.topbar-left {
  min-width: 220px;
  justify-content: flex-start;
}
.topbar-right {
  min-width: 220px;
  justify-content: flex-end;
  text-align: right;
}
.topbar-logo {
  height: 70px;
  width: auto;
  display: block;
  object-fit: contain;
}
.topbar-logo-large {
  height: 60px;
}
.topbar-center {
  flex: 1;
  text-align: center;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 6px;
}
.topbar-title {
  font-size: 26px;
  font-weight: 700;
  color: #ffffff;
  letter-spacing: 3px;
  font-family: var(--font-math);
}
.topbar-subtitle {
  font-size: 13px;
  color: rgba(255, 255, 255, 0.7);
  letter-spacing: 2px;
}
.topbar-right-text {
  display: flex;
  flex-direction: column;
  gap: 3px;
  line-height: 1.3;
}
.topbar-school {
  font-size: 20px;
  font-weight: 600;
  color: #ffffff;
  letter-spacing: 2px;
  font-family: var(--font-math);
}
.topbar-school-en {
  font-size: 12px;
  color: var(--gold-light);
  letter-spacing: 1.5px;
  font-weight: 500;
}

@media (max-width: 900px) {
  .topbar { height: 80px; }
  .topbar-left, .topbar-right { min-width: 0; }
  .topbar-logo { height: 48px; }
  .topbar-logo-large { height: 54px; }
  .topbar-title { font-size: 16px; letter-spacing: 1.5px; }
  .topbar-subtitle { font-size: 10px; }
  .topbar-school { font-size: 14px; }
  .topbar-school-en { font-size: 9px; }
  .nav { top: 80px !important; }
  .page-layout, .page-header, .hero.flex-section { padding-top: calc(80px + var(--nav-height) + 16px) !important; }
}

/* === Navigation === */
.nav {
  position: fixed;
  top: 120px;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background: var(--bg-nav);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border-light);
  z-index: 1000;
  transition: var(--transition);
}

.nav.scrolled {
  box-shadow: var(--shadow-md);
  border-bottom-color: rgba(26, 115, 232, 0.2);
}

.nav-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 24px;
}

.nav-logo {
  display: flex;
  align-items: center;
  gap: 12px;
  text-decoration: none;
  color: var(--text-heading);
}

.nav-logo-icon {
  width: 48px;
  height: 48px;
  background: linear-gradient(135deg, var(--gold), var(--gold-dark));
  border-radius: 10px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-math);
  font-size: 22px;
  font-weight: bold;
  color: #ffffff;
  position: relative;
  overflow: hidden;
}

.nav-logo-icon::after {
  content: '';
  position: absolute;
  top: -50%;
  left: -50%;
  width: 200%;
  height: 200%;
  background: radial-gradient(circle, rgba(255,255,255,0.25) 0%, transparent 60%);
  animation: logoShine 3s ease-in-out infinite;
}

@keyframes logoShine {
  0%, 100% { transform: translate(-30%, -30%); }
  50% { transform: translate(30%, 30%); }
}

.nav-logo-text {
  font-family: var(--font-math);
  font-size: 18px;
  font-weight: 700;
  letter-spacing: 0.5px;
  color: var(--gold-light);
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 4px;
  list-style: none;
}

.nav-links a {
  display: block;
  padding: 10px 18px;
  color: var(--text-secondary);
  text-decoration: none;
  font-size: 16px;
  font-weight: 600;
  border-radius: 6px;
  transition: var(--transition-fast);
  position: relative;
}

.nav-links a:hover,
.nav-links a.active {
  color: var(--gold-light);
  background: rgba(201, 169, 110, 0.08);
}

.nav-links > li > a::after,
.nav-links > li.nav-dropdown > a::after {
  content: '';
  position: absolute;
  bottom: 2px;
  left: 50%;
  transform: translateX(-50%) scaleX(0);
  width: 20px;
  height: 2px;
  background: var(--gold);
  border-radius: 1px;
  transition: transform var(--transition-fast);
}

.nav-links > li > a.active::after,
.nav-links > li.nav-dropdown > a.active::after {
  transform: translateX(-50%) scaleX(1);
}

/* === Nav Dropdown === */
.nav-dropdown {
  position: relative;
}

.nav-dropdown .dropdown-menu {
  display: none;
  position: absolute;
  top: 100%;
  left: 0;
  background: var(--bg-card);
  border: 1px solid var(--border-light);
  border-radius: 8px;
  box-shadow: var(--shadow-lg);
  min-width: 180px;
  padding: 8px 0;
  z-index: 1100;
  list-style: none;
}

.nav-dropdown:hover .dropdown-menu {
  display: block;
}

.nav-dropdown .dropdown-menu li a {
  display: block;
  padding: 10px 20px;
  font-size: 13px;
  color: var(--text-secondary);
  white-space: nowrap;
}

.nav-dropdown .dropdown-menu li a:hover {
  background: rgba(0, 51, 102, 0.05);
  color: var(--gold);
}

.nav-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  cursor: pointer;
  padding: 8px;
  background: none;
  border: none;
}

.nav-toggle span {
  display: block;
  width: 24px;
  height: 2px;
  background: var(--gold);
  border-radius: 1px;
  transition: var(--transition-fast);
}

/* === Hero Section === */
.hero {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  overflow: hidden;
  z-index: 1;
}

/* 首页使用 flex-section 布局时覆盖 */
.hero.flex-section {
  min-height: auto;
  padding: calc(120px + var(--nav-height) + 40px) 24px 60px;
}

.hero::before {
  content: '';
  position: absolute;
  inset: 0;
  background: 
    radial-gradient(ellipse at 20% 50%, rgba(26, 115, 232, 0.06) 0%, transparent 50%),
    radial-gradient(ellipse at 80% 30%, rgba(13, 148, 136, 0.04) 0%, transparent 50%),
    radial-gradient(ellipse at 50% 80%, rgba(124, 58, 237, 0.04) 0%, transparent 50%);
  z-index: -1;
}

.hero-content {
  max-width: 900px;
  z-index: 2;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 8px 22px;
  background: rgba(201, 162, 39, 0.12);
  border: 1px solid rgba(201, 162, 39, 0.35);
  border-radius: 50px;
  font-size: 14px;
  color: var(--gold-light);
  letter-spacing: 1px;
  margin-bottom: 32px;
  animation: fadeInUp 0.8s ease-out;
}

.hero-badge::before {
  content: '✦';
  font-size: 12px;
}

.hero-title {
  font-family: var(--font-math);
  font-size: clamp(32px, 5.5vw, 56px);
  font-weight: 700;
  color: var(--text-heading);
  line-height: 1.3;
  margin-bottom: 16px;
  letter-spacing: 1px;
  animation: fadeInUp 0.8s ease-out 0.1s both;
}

.hero-title .gold {
  background: linear-gradient(135deg, var(--gold-light), var(--gold), var(--gold-dark));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero-subtitle {
  font-family: var(--font-math);
  font-size: clamp(17px, 2.8vw, 24px);
  color: var(--text-secondary);
  margin-bottom: 20px;
  font-style: italic;
  animation: fadeInUp 0.8s ease-out 0.2s both;
}

.hero-meta {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 28px;
  margin-bottom: 40px;
  animation: fadeInUp 0.8s ease-out 0.3s both;
}

.hero-meta-item {
  display: flex;
  align-items: center;
  gap: 8px;
  color: var(--text-muted);
  font-size: 15px;
}

.hero-meta-item .icon {
  font-size: 20px;
  color: var(--gold);
}

.hero-buttons {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 16px;
  animation: fadeInUp 0.8s ease-out 0.4s both;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 13px 30px;
  font-size: 15px;
  font-weight: 600;
  border-radius: 50px;
  text-decoration: none;
  cursor: pointer;
  border: none;
  transition: var(--transition);
  letter-spacing: 0.5px;
}

.btn-primary {
  background: linear-gradient(135deg, var(--gold), var(--gold-dark));
  color: #ffffff;
  box-shadow: 0 4px 15px rgba(26, 115, 232, 0.25);
}

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 25px rgba(26, 115, 232, 0.4);
}

.btn-outline {
  background: transparent;
  color: var(--gold);
  border: 1.5px solid var(--gold);
}

.btn-outline:hover {
  background: rgba(26, 115, 232, 0.06);
  transform: translateY(-2px);
}

.btn-sm {
  padding: 8px 20px;
  font-size: 13px;
}

/* === Section Common === */
.section {
  position: relative;
  z-index: 1;
  padding: 48px 24px;
}

.section.flex-section {
  flex: 1;
  padding: 0 24px 48px;
  max-width: var(--max-width);
  margin: 0 auto;
  width: 100%;
}

/* 跟在 page-header 后面的 section 不需要顶部导航偏移 */
.page-header + .section.flex-section {
  padding-top: 0;
}

/* no-sidebar 页面中的 section-header 更紧凑 */
.page-layout.no-sidebar .section-header {
  margin-bottom: 24px;
}

/* no-sidebar 页面中的 page-header 内部使用更紧凑 padding */
.page-layout.no-sidebar .page-header {
  padding-top: 0;
  padding-bottom: 16px;
}

.section-alt {
  background: var(--bg-secondary);
}

.section-inner {
  max-width: var(--max-width);
  margin: 0 auto;
}

.section-header {
  text-align: center;
  margin-bottom: 32px;
}

.section-label {
  display: inline-block;
  font-size: 12px;
  letter-spacing: 3px;
  color: var(--gold);
  text-transform: uppercase;
  margin-bottom: 12px;
}

.section-title {
  font-family: var(--font-math);
  font-size: clamp(26px, 4vw, 40px);
  font-weight: 700;
  color: var(--text-heading);
  margin-bottom: 16px;
}

.section-desc {
  max-width: 700px;
  margin: 0 auto;
  color: var(--text-secondary);
  font-size: 16px;
  line-height: 1.8;
}

/* === Divider with Math Symbol === */
.math-divider {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 20px;
  margin: 20px 0;
}

.math-divider::before,
.math-divider::after {
  content: '';
  flex: 0 0 60px;
  height: 1px;
  background: var(--border);
}

.math-divider span {
  font-family: var(--font-math);
  font-size: 18px;
  color: var(--gold);
}

/* === Card Grid === */
.card-grid {
  display: grid;
  gap: 24px;
  margin-top: 24px;
}

.card-grid-2 { grid-template-columns: repeat(auto-fit, minmax(380px, 1fr)); }
.card-grid-3 { grid-template-columns: repeat(auto-fit, minmax(340px, 1fr)); }
.card-grid-4 { grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); }

.card {
  background: var(--bg-card);
  border: 1px solid var(--border-light);
  border-radius: var(--border-radius-lg);
  padding: 32px;
  transition: var(--transition);
  position: relative;
  overflow: hidden;
  box-shadow: var(--shadow-sm);
}

.card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--gold), var(--purple));
  opacity: 0;
  transition: var(--transition);
}

.card:hover {
  background: var(--bg-card-hover);
  border-color: rgba(26, 115, 232, 0.2);
  transform: translateY(-3px);
  box-shadow: var(--shadow-md);
}

.card:hover::before {
  opacity: 1;
}

.card-icon {
  width: 50px;
  height: 50px;
  background: rgba(26, 115, 232, 0.08);
  border-radius: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 22px;
  color: var(--gold);
  margin-bottom: 20px;
}

.card-title {
  font-family: var(--font-math);
  font-size: 20px;
  font-weight: 600;
  color: var(--text-heading);
  margin-bottom: 12px;
}

.card-text {
  color: var(--text-secondary);
  font-size: 14px;
  line-height: 1.8;
}

/* === Overview Stats === */
.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 20px;
  margin-top: 40px;
}

.stat-card {
  text-align: center;
  padding: 28px 20px;
  background: var(--bg-card);
  border: 1px solid var(--border-light);
  border-radius: var(--border-radius-lg);
  transition: var(--transition);
}

.stat-card:hover {
  border-color: var(--gold);
  box-shadow: var(--shadow-gold);
  transform: translateY(-2px);
}

.stat-number {
  font-family: var(--font-math);
  font-size: 42px;
  font-weight: 700;
  color: var(--gold);
  line-height: 1.2;
}

.stat-label {
  color: var(--text-muted);
  font-size: 14px;
  margin-top: 8px;
}

/* === Lecturer Card === */
.lecturer-card {
  display: flex;
  gap: 20px;
  padding: 24px;
}

.lecturer-avatar {
  width: 80px;
  height: 120px;
  border-radius: 50%;
  border: 2px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-math);
  font-size: 28px;
  color: var(--gold);
  overflow: hidden;
  transition: var(--transition);
}

.lecturer-card:hover .lecturer-avatar {
  border-color: var(--gold);
  box-shadow: 0 0 0 4px var(--gold-glow);
}

.lecturer-avatar img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.lecturer-info h3 {
  font-family: var(--font-math);
  font-size: 18px;
  font-weight: 600;
  color: var(--text-heading);
  margin-bottom: 4px;
}

.lecturer-info .title {
  color: var(--gold);
  font-size: 13px;
  margin-bottom: 4px;
}

.lecturer-info .affiliation {
  color: var(--text-secondary);
  font-size: 13px;
  margin-bottom: 8px;
}

.lecturer-info .desc {
  color: var(--text-muted);
  font-size: 13px;
  line-height: 1.6;
}

/* === Schedule Table === */
.schedule-week {
  margin-bottom: 48px;
}

.schedule-week-title {
  font-family: var(--font-math);
  font-size: 22px;
  color: var(--gold-light);
  margin-bottom: 20px;
  padding-bottom: 12px;
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  gap: 12px;
}

.schedule-week-title .week-num {
  background: var(--gold-dark);
  color: #0a0a0f;
  padding: 4px 14px;
  border-radius: 20px;
  font-size: 14px;
  font-weight: 700;
}

.schedule-table-wrap {
  overflow-x: auto;
}

.schedule-table {
  width: 100%;
  border-collapse: collapse;
  min-width: 800px;
}

.schedule-table th {
  background: var(--gold);
  color: #ffffff;
  font-weight: 600;
  font-size: 13px;
  padding: 14px 12px;
  border: 1px solid var(--gold-dark);
  text-align: center;
  white-space: nowrap;
}

.schedule-table td {
  padding: 12px;
  border: 1px solid var(--border-light);
  vertical-align: top;
  font-size: 13px;
  line-height: 1.6;
}

.schedule-table .time-cell {
  background: var(--bg-card);
  color: var(--gold-light);
  font-weight: 600;
  text-align: center;
  white-space: nowrap;
  font-size: 12px;
}

.schedule-table .topic {
  color: var(--text-primary);
  font-weight: 500;
}

.schedule-table .lecturer-name {
  color: var(--gold);
  font-size: 12px;
  margin-top: 4px;
}

.schedule-table .discussion {
  background: rgba(201, 169, 110, 0.04);
  color: var(--teal);
  font-weight: 500;
  text-align: center;
}

/* === Course Module === */
.module-card {
  padding: 28px;
}

.module-card .module-hours {
  display: inline-block;
  padding: 3px 12px;
  background: rgba(26, 115, 232, 0.08);
  color: var(--gold);
  border-radius: 20px;
  font-size: 12px;
  margin-bottom: 14px;
  font-weight: 600;
}

.module-card .module-topics {
  list-style: none;
  margin-top: 14px;
}

.module-card .module-topics li {
  position: relative;
  padding-left: 18px;
  color: var(--text-secondary);
  font-size: 13px;
  margin-bottom: 6px;
}

.module-card .module-topics li::before {
  content: '▸';
  position: absolute;
  left: 0;
  color: var(--gold);
  font-size: 10px;
  top: 2px;
}

/* === Timeline === */
.timeline {
  position: relative;
  padding-left: 30px;
}

.timeline::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0;
  bottom: 0;
  width: 2px;
  background: linear-gradient(180deg, var(--gold), transparent);
}

.timeline-item {
  position: relative;
  margin-bottom: 32px;
  padding-left: 28px;
}

.timeline-item::before {
  content: '';
  position: absolute;
  left: -34px;
  top: 6px;
  width: 10px;
  height: 10px;
  background: var(--gold);
  border-radius: 50%;
  box-shadow: 0 0 10px var(--gold-glow);
}

.timeline-date {
  font-size: 13px;
  color: var(--gold);
  margin-bottom: 4px;
}

.timeline-title {
  font-size: 16px;
  font-weight: 600;
  color: var(--text-heading);
  margin-bottom: 6px;
}

.timeline-desc {
  color: var(--text-secondary);
  font-size: 14px;
}

/* === Form Styles === */
.form-group {
  margin-bottom: 24px;
}

.form-label {
  display: block;
  font-size: 14px;
  color: var(--text-secondary);
  margin-bottom: 8px;
  font-weight: 500;
}

.form-label .required {
  color: #e05555;
  margin-left: 4px;
}

.form-input,
.form-textarea,
.form-select {
  width: 100%;
  padding: 12px 16px;
  background: var(--bg-primary);
  border: 1.5px solid var(--border-light);
  border-radius: 8px;
  color: var(--text-primary);
  font-size: 14px;
  font-family: var(--font-body);
  transition: var(--transition-fast);
}

.form-input:focus,
.form-textarea:focus,
.form-select:focus {
  outline: none;
  border-color: var(--gold);
  box-shadow: 0 0 0 3px var(--gold-glow);
  background: var(--bg-card);
}

.form-textarea {
  min-height: 100px;
  resize: vertical;
}
.form-select {
  cursor: pointer;
  appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 12 12'%3E%3Cpath fill='%23c9a96e' d='M6 8L1 3h10z'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 16px center;
}

.form-select option {
  background: var(--bg-card);
  color: var(--text-primary);
}

.form-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 20px;
}

.form-hint {
  font-size: 12px;
  color: var(--text-muted);
  margin-top: 6px;
}

/* === Footer === */
.footer {
  background: #003087;
  border-top: 3px solid var(--gold);
  padding: 22px 24px 14px;
  position: relative;
  z-index: 1;
  color: rgba(255, 255, 255, 0.85);
}

.footer .footer-brand h3 { color: #ffffff; font-size: 16px; margin-bottom: 8px; }
.footer .footer-brand p { color: rgba(255, 255, 255, 0.82); font-size: 12px; line-height: 1.6; }
.footer .footer-links h4 { color: #ffffff; font-size: 13px; margin-bottom: 10px; }
.footer .footer-links a { color: rgba(255, 255, 255, 0.82); font-size: 12px; margin-bottom: 7px; }
.footer .footer-links a:hover { color: var(--gold-light); }
.footer .footer-bottom { border-top-color: rgba(255,255,255,0.18); padding-top: 12px; margin-top: 14px; }
.footer .footer-bottom p { color: rgba(255, 255, 255, 0.7); font-size: 11px; }
.footer .supported-by { color: var(--gold-light); font-size: 11px; }
.footer .footer-bottom .icp-beian { color: rgba(255, 255, 255, 0.85); font-size: 11px; text-decoration: none; border: 1px solid rgba(255,255,255,0.25); padding: 2px 8px; border-radius: 4px; }
.footer .footer-bottom .icp-beian:hover { color: #fff; border-color: var(--gold-light); }

.footer-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  display: grid;
  grid-template-columns: 1.2fr 0.8fr 0.8fr 0.8fr 0.8fr;
  gap: 20px;
}

.footer-brand h3 {
  font-family: var(--font-math);
  font-size: 15px;
  color: var(--gold-light);
  margin-bottom: 8px;
}

.footer-brand p {
  color: var(--text-muted);
  font-size: 12px;
  line-height: 1.6;
}

.footer-links h4 {
  font-size: 13px;
  color: var(--text-heading);
  margin-bottom: 10px;
}

.footer-links a {
  display: block;
  color: var(--text-muted);
  text-decoration: none;
  font-size: 12px;
  margin-bottom: 6px;
  transition: var(--transition-fast);
}

.footer-links a:hover {
  color: var(--gold-light);
}

.footer-bottom {
  max-width: var(--max-width);
  margin: 30px auto 0;
  padding-top: 20px;
  border-top: 1px solid var(--border-light);
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 12px;
}

.footer-bottom p {
  color: var(--text-muted);
  font-size: 12px;
}

.footer-bottom .supported-by {
  display: flex;
  align-items: center;
  gap: 8px;
  color: var(--gold);
  font-size: 12px;
}

/* === Page Header (inner pages) === */
.page-header {
  padding: calc(120px + var(--nav-height) + 24px) 24px 20px;
  text-align: center;
  position: relative;
  z-index: 1;
  flex-shrink: 0;
}

.page-header::before {
  content: '';
  position: absolute;
  inset: 0;
  background: radial-gradient(ellipse at center, rgba(26, 115, 232, 0.05) 0%, transparent 70%);
  z-index: -1;
}

.page-header .breadcrumb {
  font-size: 13px;
  color: var(--text-muted);
  margin-bottom: 16px;
}

.page-header .breadcrumb a {
  color: var(--gold);
  text-decoration: none;
}

.page-header h1 {
  font-family: var(--font-math);
  font-size: clamp(28px, 4vw, 42px);
  font-weight: 700;
  color: var(--text-heading);
  margin-bottom: 6px;
}

.page-header .subtitle {
  color: var(--text-secondary);
  font-size: 15px;
}

/* === Content Sections === */
.page-content > .content-section {
  display: none !important;
  padding: 0 0 40px 0;
}
.page-content > .content-section.active {
  display: block !important;
}

.content-section h2 {
  font-family: var(--font-math);
  font-size: 30px;
  color: var(--text-heading);
  margin-bottom: 20px;
  padding-bottom: 12px;
  border-bottom: 1px solid var(--border);
}

.content-section h3 {
  font-family: var(--font-math);
  font-size: 20px;
  color: var(--gold-light);
  margin: 28px 0 14px;
}

.content-section p {
  color: var(--text-secondary);
  line-height: 1.9;
  margin-bottom: 16px;
}

.content-section ul, .content-section ol {
  color: var(--text-secondary);
  padding-left: 24px;
  margin-bottom: 16px;
}

.content-section li {
  margin-bottom: 8px;
  line-height: 1.8;
}

/* === Committee Grid === */
.committee-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 16px;
}

.committee-card {
  display: flex;
  align-items: center;
  gap: 14px;
  padding: 18px 20px;
  background: var(--bg-card);
  border: 1px solid var(--border-light);
  border-radius: var(--border-radius);
  transition: var(--transition);
  box-shadow: var(--shadow-sm);
}

.committee-card:hover {
  border-color: var(--gold);
}

.committee-card .role-badge {
  padding: 4px 12px;
  background: rgba(0, 51, 102, 0.08);
  color: var(--gold);
  border: 1px solid rgba(0, 51, 102, 0.2);
  border-radius: 20px;
  font-size: 11px;
  font-weight: 600;
  white-space: nowrap;
}

.committee-card .role-badge.chair {
  background: linear-gradient(135deg, #c41230, #a00d24);
  color: #fff;
  border: none;
}

.committee-info h4 {
  font-size: 15px;
  color: var(--text-heading);
  margin-bottom: 2px;
}

.committee-info .aff {
  font-size: 13px;
  color: var(--text-muted);
}

/* === Resource List === */
.resource-list {
  list-style: none;
}

.resource-list li {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 14px 20px;
  background: var(--bg-card);
  border: 1px solid var(--border-light);
  border-radius: 8px;
  margin-bottom: 10px;
  transition: var(--transition-fast);
  box-shadow: var(--shadow-sm);
}

.resource-list li:hover {
  border-color: var(--gold);
  background: var(--gold-glow);
  box-shadow: var(--shadow-md);
}

.resource-list .icon {
  font-size: 20px;
  color: var(--gold);
}

.resource-list .name {
  flex: 1;
  color: var(--text-primary);
  font-weight: 500;
}

.resource-list .tag {
  padding: 2px 10px;
  background: rgba(201, 169, 110, 0.1);
  color: var(--gold-light);
  border-radius: 20px;
  font-size: 11px;
}

/* === Contact Info === */
.contact-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 40px;
}

.contact-info-item {
  display: flex;
  gap: 16px;
  margin-bottom: 24px;
}

.contact-info-item .icon {
  font-size: 22px;
  color: var(--gold);
  flex-shrink: 0;
  width: 40px;
  height: 40px;
  background: rgba(201, 169, 110, 0.08);
  border-radius: 10px;
  display: flex;
  align-items: center;
  justify-content: center;
}

.contact-info-item h4 {
  font-size: 14px;
  color: var(--text-heading);
  margin-bottom: 4px;
}

.contact-info-item p {
  color: var(--text-secondary);
  font-size: 14px;
}

/* === News List === */
.news-item {
  display: flex;
  gap: 20px;
  padding: 20px;
  background: var(--bg-card);
  border: 1px solid var(--border-light);
  border-radius: var(--border-radius);
  margin-bottom: 16px;
  transition: var(--transition);
  text-decoration: none;
  color: inherit;
  box-shadow: var(--shadow-sm);
}

.news-item:hover {
  border-color: var(--gold);
  background: var(--bg-card-hover);
  box-shadow: var(--shadow-md);
}

.news-date {
  flex-shrink: 0;
  width: 60px;
  text-align: center;
}

.news-date .day {
  font-family: var(--font-math);
  font-size: 28px;
  font-weight: 700;
  color: var(--gold);
  line-height: 1;
}

.news-date .month {
  font-size: 12px;
  color: var(--text-muted);
}

.news-content h4 {
  font-size: 16px;
  color: var(--text-heading);
  margin-bottom: 6px;
}

.news-content p {
  color: var(--text-secondary);
  font-size: 13px;
  line-height: 1.6;
}

/* === Modal === */
.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.8);
  z-index: 2000;
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 0;
  pointer-events: none;
  transition: var(--transition);
}

.modal-overlay.active {
  opacity: 1;
  pointer-events: auto;
}

.modal {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--border-radius-lg);
  padding: 40px;
  max-width: 500px;
  width: 90%;
  text-align: center;
}

.modal h3 {
  font-family: var(--font-math);
  font-size: 22px;
  color: var(--text-heading);
  margin-bottom: 12px;
}

.modal p {
  color: var(--text-secondary);
  margin-bottom: 24px;
}

/* === Animations === */
@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(30px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

@keyframes float {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(-10px); }
}

@keyframes pulse {
  0%, 100% { opacity: 0.5; }
  50% { opacity: 1; }
}

.animate-in {
  animation: fadeInUp 0.6s ease-out both;
}

/* === Responsive === */
@media (max-width: 1024px) {
  .footer-inner {
    grid-template-columns: 1fr 1fr;
  }
  
  .contact-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 768px) {
  .nav-links {
    position: fixed;
    top: var(--nav-height);
    left: 0;
    right: 0;
    bottom: 0;
    background: var(--bg-nav);
    backdrop-filter: blur(20px);
    flex-direction: column;
    justify-content: flex-start;
    padding: 24px;
    gap: 8px;
    transform: translateX(100%);
    transition: var(--transition);
    z-index: 999;
  }
  
  .nav-links.active {
    transform: translateX(0);
  }
  
  .nav-links a {
    font-size: 16px;
    padding: 14px 20px;
  }
  
  .nav-toggle {
    display: flex;
  }
  
  .hero {
    min-height: auto;
    padding-top: calc(var(--nav-height) + 40px);
    padding-bottom: 60px;
  }
  
  .card-grid-2,
  .card-grid-3,
  .card-grid-4 {
    grid-template-columns: 1fr;
  }
  
  .lecturer-card {
    flex-direction: column;
    align-items: center;
    text-align: center;
  }
  
  .stats-grid {
    grid-template-columns: repeat(2, 1fr);
  }
  
  .form-row {
    grid-template-columns: 1fr;
  }
  
  .footer-inner {
    grid-template-columns: 1fr;
  }
  
  .footer-bottom {
    flex-direction: column;
    text-align: center;
  }
  
  .hero-meta {
    flex-direction: column;
    align-items: center;
    gap: 12px;
  }
  
  .committee-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 480px) {
  .stats-grid {
    grid-template-columns: 1fr;
  }
  
  .section {
    padding: 50px 16px;
  }
  
  .card {
    padding: 24px;
  }
}

/* === Page with Sidebar Layout === */
.page-layout {
  display: flex;
  gap: 32px;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: calc(120px + var(--nav-height) + 32px) 24px 60px;
  width: 100%;
  align-items: flex-start;
}

.page-sidebar {
  width: 200px;
  flex-shrink: 0;
  position: sticky;
  top: calc(120px + var(--nav-height) + 16px);
  align-self: flex-start;
}

/* sidebar 隐藏时内容区全宽 */
.page-sidebar[style*="display: none"] + .page-content {
  max-width: 100%;
}

/* 线上直播、联系我们不需要 sidebar 时的全宽布局 */
.page-layout.no-sidebar {
  padding: calc(120px + var(--nav-height) + 32px) 24px 60px;
}
.page-layout.no-sidebar .page-content {
  max-width: 100%;
}

.page-sidebar-title {
  font-family: var(--font-math);
  font-size: 16px;
  font-weight: 700;
  color: var(--text-heading);
  margin-bottom: 16px;
  padding-bottom: 12px;
  border-bottom: 2px solid var(--gold);
}

.page-sidebar ul {
  list-style: none;
  padding: 0;
}

.page-sidebar ul li a {
  display: block;
  padding: 10px 14px;
  font-size: 14px;
  color: var(--text-secondary);
  text-decoration: none;
  border-radius: 6px;
  margin-bottom: 2px;
  transition: var(--transition-fast);
  border-left: 3px solid transparent;
}

.page-sidebar ul li a:hover {
  background: rgba(0, 51, 102, 0.05);
  color: var(--gold);
  border-left-color: var(--gold);
}

.page-sidebar ul li a.active {
  background: rgba(0, 51, 102, 0.08);
  color: var(--gold);
  border-left-color: var(--gold);
  font-weight: 600;
}

.page-content {
  flex: 1;
  min-width: 0;
}

.page-content .content-section:first-child {
  margin-top: 0;
}

@media (max-width: 768px) {
  .page-layout {
    flex-direction: column;
    padding: calc(120px + var(--nav-height) + 16px) 16px 40px;
  }
  .page-sidebar {
    width: 100%;
    position: static;
    margin-bottom: 20px;
    padding-bottom: 16px;
    border-bottom: 1px solid var(--border-light);
  }
  .page-sidebar ul {
    display: flex;
    flex-wrap: wrap;
    gap: 6px;
  }
  .page-sidebar ul li a {
    border-left: none;
    border-bottom: 2px solid transparent;
    padding: 8px 12px;
    font-size: 13px;
  }
}

/* === Print === */
@media print {
  .nav, .footer, #math-bg { display: none; }
  body { background: white; color: black; }
}