/* ==================== 全局样式 ==================== */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --primary-color: #000000;
  --primary-hover: #333333;
  --secondary-color: #666666;
  --success-color: #000000;
  --warning-color: #666666;
  --text-primary: #000000;
  --text-secondary: #666666;
  --bg-primary: #ffffff;
  --bg-secondary: #f5f5f5;
  --border-color: #e0e0e0;
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 2px 4px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 4px 8px rgba(0, 0, 0, 0.1);
  --shadow-xl: 0 8px 16px rgba(0, 0, 0, 0.15);
  --radius-sm: 4px;
  --radius-md: 6px;
  --radius-lg: 8px;
  --transition: all 0.2s ease;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen',
    'Ubuntu', 'Cantarell', 'Fira Sans', 'Droid Sans', 'Helvetica Neue', sans-serif;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  background: #ffffff;
  min-height: 100vh;
  color: var(--text-primary);
  line-height: 1.6;
}

.container {
  max-width: 1400px;
  margin: 0 auto;
  padding: 20px;
}

/* ==================== 头部导航 ==================== */
.header {
  background: #ffffff;
  border-bottom: 1px solid var(--border-color);
  position: sticky;
  top: 0;
  z-index: 100;
  padding: 16px 0;
}

.header-content {
  max-width: 1400px;
  margin: 0 auto;
  padding: 0 20px;
  display: flex;
  justify-content: center;
  align-items: center;
}

.logo {
  font-size: 24px;
  font-weight: 700;
  color: var(--text-primary);
  cursor: pointer;
  letter-spacing: 2px;
  text-transform: uppercase;
}

.nav-links {
  display: flex;
  gap: 24px;
  align-items: center;
}

.nav-link {
  color: var(--text-secondary);
  text-decoration: none;
  font-weight: 500;
  transition: var(--transition);
  padding: 8px 16px;
  border-radius: var(--radius-sm);
}

.nav-link:hover {
  color: var(--primary-color);
  background: var(--bg-secondary);
}

/* ==================== 课程列表页样式 ==================== */
.page-title {
  color: var(--text-primary);
  font-size: 32px;
  font-weight: 600;
  margin: 40px 0 30px;
  text-align: center;
  letter-spacing: -0.5px;
}

.courses-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 24px;
  margin-top: 30px;
}

.course-card {
  background: var(--bg-primary);
  border-radius: var(--radius-md);
  overflow: hidden;
  border: 1px solid var(--border-color);
  transition: var(--transition);
  cursor: pointer;
  position: relative;
}

.course-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
  border-color: var(--text-primary);
}

.course-thumbnail {
  width: 100%;
  height: 220px;
  object-fit: cover;
  transition: var(--transition);
}

.course-card:hover .course-thumbnail {
  transform: scale(1.05);
}

.course-badge {
  position: absolute;
  top: 12px;
  right: 12px;
  background: var(--text-primary);
  color: white;
  padding: 6px 12px;
  border-radius: var(--radius-sm);
  font-size: 13px;
  font-weight: 600;
}

.course-info {
  padding: 16px;
}

.course-title {
  font-size: 16px;
  font-weight: 600;
  color: var(--text-primary);
  line-height: 1.5;
  margin: 0;
}

.course-meta {
  display: flex;
  gap: 16px;
  margin-bottom: 12px;
  flex-wrap: wrap;
}

.meta-item {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 14px;
  color: var(--text-secondary);
}

.meta-icon {
  width: 16px;
  height: 16px;
}

.course-description {
  font-size: 14px;
  color: var(--text-secondary);
  margin-bottom: 16px;
  line-height: 1.6;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.course-footer {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-top: 16px;
  border-top: 1px solid var(--border-color);
}

.course-price {
  font-size: 20px;
  font-weight: 600;
  color: var(--text-primary);
}

.course-rating {
  display: flex;
  align-items: center;
  gap: 4px;
  font-size: 14px;
  color: var(--text-secondary);
  font-weight: 500;
}

.star-icon {
  width: 16px;
  height: 16px;
  fill: currentColor;
}

/* ==================== 课程详情页样式 ==================== */
.course-detail-container {
  background: var(--bg-primary);
  border-radius: var(--radius-md);
  overflow: hidden;
  border: 1px solid var(--border-color);
  margin-top: 30px;
}

/* PC端布局：左右分栏 */
.course-detail-layout {
  display: grid;
  grid-template-columns: 3fr 1fr;
  gap: 0;
  height: calc(100vh - 80px);
}

/* 左侧内容区 */
.course-main-content {
  display: flex;
  flex-direction: column;
  background: var(--bg-primary);
  overflow: hidden;
}

.video-container {
  position: relative;
  width: 100%;
  flex: 1;
  background: #000;
  overflow: hidden;
}

.video-player {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  object-fit: contain;
}

.course-detail-info {
  padding: 24px 32px;
  border-top: 1px solid var(--border-color);
}

.detail-header {
  margin-bottom: 24px;
}

.detail-title {
  font-size: 32px;
  font-weight: 700;
  margin-bottom: 16px;
  color: var(--text-primary);
  line-height: 1.3;
}

.detail-meta {
  display: flex;
  gap: 24px;
  flex-wrap: wrap;
  margin-bottom: 20px;
}

.detail-meta-item {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 16px;
  color: var(--text-secondary);
}

.detail-description {
  font-size: 16px;
  line-height: 1.8;
  color: var(--text-secondary);
  margin-bottom: 24px;
}

.instructor-section {
  padding: 24px;
  background: var(--bg-secondary);
  border-radius: var(--radius-md);
  margin-top: 24px;
}

.instructor-label {
  font-size: 14px;
  color: var(--text-secondary);
  margin-bottom: 8px;
  text-transform: uppercase;
  letter-spacing: 1px;
}

.instructor-name {
  font-size: 20px;
  font-weight: 600;
  color: var(--text-primary);
}

/* 右侧单元列表 */
.course-sidebar {
  background: var(--bg-secondary);
  border-left: 1px solid var(--border-color);
  display: flex;
  flex-direction: column;
  overflow: hidden;
  height: 100%;
}

.sidebar-header {
  padding: 20px;
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border-color);
}

.sidebar-title {
  font-size: 16px;
  font-weight: 600;
  margin-bottom: 4px;
  color: var(--text-primary);
}

.sidebar-subtitle {
  font-size: 13px;
  color: var(--text-secondary);
}

.units-list {
  padding: 16px;
  overflow-y: auto;
  flex: 1;
}

.unit-item {
  margin-bottom: 8px;
  background: var(--bg-primary);
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  overflow: hidden;
}

.unit-header {
  padding: 14px 16px;
  background: var(--bg-secondary);
  cursor: pointer;
  transition: var(--transition);
  border-bottom: 1px solid var(--border-color);
}

.unit-header:hover {
  background: #ebebeb;
}

.unit-title {
  font-size: 16px;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 4px;
}

.unit-progress {
  font-size: 12px;
  color: var(--text-secondary);
}

.lessons-list {
  padding: 0;
}

.lesson-item {
  padding: 12px 16px;
  border-bottom: 1px solid var(--border-color);
  cursor: pointer;
  transition: var(--transition);
  display: flex;
  align-items: center;
  gap: 12px;
}

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

.lesson-item:hover {
  background: var(--bg-secondary);
}

/* 正在播放的单元 */
.lesson-item.playing {
  background: #e8f5e9;
  border-left: 3px solid #4caf50;
}

.lesson-item.playing .lesson-title {
  color: #2e7d32;
  font-weight: 600;
}

/* 即将播放的单元 */
.lesson-item.next {
  background: #fff3e0;
  border-left: 3px solid #ff9800;
}

.lesson-item.next .lesson-title {
  color: #e65100;
}

.lesson-status {
  width: 20px;
  height: 20px;
  border-radius: 50%;
  border: 2px solid var(--border-color);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.lesson-status.completed {
  background: var(--text-primary);
  border-color: var(--text-primary);
}

.lesson-status.completed::after {
  content: '✓';
  color: white;
  font-size: 12px;
  font-weight: bold;
}

.lesson-info {
  flex: 1;
}

.lesson-title {
  font-size: 14px;
  color: var(--text-primary);
  margin-bottom: 4px;
}

.lesson-duration {
  font-size: 12px;
  color: var(--text-secondary);
}

.lesson-status-text {
  font-size: 11px;
  font-weight: 600;
  margin-top: 2px;
}

.lesson-item.playing .lesson-status-text {
  color: #4caf50;
}

.lesson-item.next .lesson-status-text {
  color: #ff9800;
}

/* ==================== 移动端适配 ==================== */
@media (max-width: 768px) {
  .container {
    padding: 12px;
  }

  .page-title {
    font-size: 28px;
    margin: 24px 0 20px;
  }

  .courses-grid {
    grid-template-columns: 1fr;
    gap: 16px;
  }

  .course-thumbnail {
    height: 180px;
  }

  .header-content {
    flex-direction: column;
    gap: 12px;
  }

  .nav-links {
    gap: 12px;
  }

  /* 移动端详情页布局：上下排列 */
  .course-detail-layout {
    grid-template-columns: 1fr;
    display: flex;
    flex-direction: column;
    height: auto;
    min-height: calc(100vh - 80px);
  }

  .course-sidebar {
    border-left: none;
    border-top: 1px solid var(--border-color);
    max-height: none;
    position: static;
    order: 2;
    height: auto;
  }

  .course-main-content {
    order: 1;
  }

  .video-container {
    flex: none;
    padding-bottom: 56.25%; /* 16:9 比例 */
  }

  .detail-title {
    font-size: 24px;
  }

  .detail-meta {
    gap: 16px;
  }

  .course-detail-info {
    padding: 20px;
  }

  .video-container {
    padding-bottom: 56.25%;
  }
}

/* ==================== 平板适配 ==================== */
@media (min-width: 769px) and (max-width: 1024px) {
  .courses-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .course-detail-layout {
    grid-template-columns: 2fr 1fr;
  }
}

/* ==================== 加载动画 ==================== */
.loading {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 400px;
}

.spinner {
  width: 40px;
  height: 40px;
  border: 3px solid var(--border-color);
  border-top-color: var(--text-primary);
  border-radius: 50%;
  animation: spin 0.6s linear infinite;
}

@keyframes spin {
  to {
    transform: rotate(360deg);
  }
}

/* ==================== 响应式工具类 ==================== */
.text-center {
  text-align: center;
}

.mt-20 {
  margin-top: 20px;
}

.mb-20 {
  margin-bottom: 20px;
}

.hidden {
  display: none !important;
}