/**
 * 课程平台 - 前台样式
 * 生产级样式表
 */

/* CSS 变量 */
:root {
  --color-primary: #4F46E5;
  --color-primary-dark: #4338CA;
  --color-success: #10B981;
  --color-warning: #F59E0B;
  --color-danger: #EF4444;
  --color-info: #3B82F6;
  
  --bg-primary: #FFFFFF;
  --bg-secondary: #F9FAFB;
  --bg-dark: #111827;
  
  --text-primary: #111827;
  --text-secondary: #6B7280;
  --text-muted: #9CA3AF;
  
  --border-color: #E5E7EB;
  --border-radius: 8px;
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
}

/* 重置 */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  font-size: 14px;
  line-height: 1.5;
  color: var(--text-primary);
  background: var(--bg-secondary);
}

.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 20px;
}

/* 按钮 */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 10px 20px;
  border: none;
  border-radius: var(--border-radius);
  font-size: 14px;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.2s;
  text-decoration: none;
}

.btn-primary {
  background: var(--color-primary);
  color: white;
}

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

.btn-outline {
  background: transparent;
  color: var(--text-primary);
  border: 1px solid var(--border-color);
}

.btn-outline:hover {
  background: var(--bg-secondary);
}

.btn-lg {
  padding: 14px 28px;
  font-size: 16px;
}

.btn-block {
  width: 100%;
}

/* 顶部导航 */
.header {
  background: var(--bg-primary);
  border-bottom: 1px solid var(--border-color);
  position: sticky;
  top: 0;
  z-index: 100;
}

.header-content {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}

.logo {
  font-size: 20px;
  font-weight: 700;
  color: var(--color-primary);
  text-decoration: none;
}

.nav {
  display: flex;
  gap: 24px;
}

.nav a {
  color: var(--text-secondary);
  text-decoration: none;
  font-weight: 500;
}

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

.user-menu {
  display: flex;
  align-items: center;
  gap: 16px;
}

/* Hero 区域 */
.hero {
  background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-primary-dark) 100%);
  color: white;
  padding: 80px 0;
  text-align: center;
}

.hero h1 {
  font-size: 40px;
  margin-bottom: 16px;
}

.hero p {
  font-size: 18px;
  opacity: 0.9;
  margin-bottom: 32px;
}

.hero-actions {
  display: flex;
  gap: 16px;
  justify-content: center;
}

.hero-actions .btn-outline {
  color: white;
  border-color: rgba(255,255,255,0.5);
}

/* 课程列表 */
.courses-section {
  padding: 60px 0;
}

.section-title {
  font-size: 28px;
  margin-bottom: 32px;
  text-align: center;
}

.courses-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 24px;
}

.course-card {
  background: var(--bg-primary);
  border-radius: 12px;
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  transition: transform 0.2s, box-shadow 0.2s;
}

.course-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
}

.course-cover {
  height: 180px;
  background: var(--bg-secondary);
  overflow: hidden;
}

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

.cover-placeholder {
  width: 100%;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 64px;
  background: linear-gradient(135deg, #E0E7FF 0%, #C7D2FE 100%);
}

.course-info {
  padding: 20px;
}

.course-info h3 {
  font-size: 18px;
  margin-bottom: 8px;
}

.course-info h3 a {
  color: var(--text-primary);
  text-decoration: none;
}

.course-info h3 a:hover {
  color: var(--color-primary);
}

.course-desc {
  color: var(--text-secondary);
  font-size: 14px;
  margin-bottom: 12px;
  line-height: 1.5;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.course-meta {
  color: var(--text-muted);
  font-size: 13px;
  margin-bottom: 16px;
}

.course-action {
  display: flex;
  gap: 8px;
}

/* 认证页面 */
.auth-box {
  max-width: 400px;
  margin: 60px auto;
  background: var(--bg-primary);
  padding: 40px;
  border-radius: 12px;
  box-shadow: var(--shadow-md);
}

.auth-box h1 {
  text-align: center;
  margin-bottom: 24px;
}

.auth-form .form-group {
  margin-bottom: 20px;
}

.auth-form label {
  display: block;
  margin-bottom: 6px;
  font-weight: 500;
}

.auth-form input {
  width: 100%;
  padding: 12px 16px;
  border: 1px solid var(--border-color);
  border-radius: var(--border-radius);
  font-size: 14px;
}

.auth-form input:focus {
  outline: none;
  border-color: var(--color-primary);
}

.auth-link {
  text-align: center;
  margin-top: 20px;
  color: var(--text-secondary);
}

.auth-link a {
  color: var(--color-primary);
  text-decoration: none;
}

/* 课程详情页 */
.course-detail {
  padding: 40px 0;
}

.course-header {
  display: grid;
  grid-template-columns: 400px 1fr;
  gap: 40px;
  margin-bottom: 40px;
}

.course-header .course-cover {
  height: 240px;
  border-radius: 12px;
}

.course-header-info h1 {
  font-size: 32px;
  margin-bottom: 16px;
}

.course-header-info p {
  color: var(--text-secondary);
  margin-bottom: 24px;
  line-height: 1.6;
}

.lessons-list {
  background: var(--bg-primary);
  border-radius: 12px;
  padding: 24px;
}

.lessons-list h2 {
  font-size: 20px;
  margin-bottom: 20px;
}

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

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

.lesson-number {
  width: 32px;
  height: 32px;
  background: var(--bg-secondary);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  margin-right: 16px;
  font-weight: 600;
  font-size: 13px;
}

.lesson-title {
  flex: 1;
}

/* 学习页面 */
.learn-container {
  display: grid;
  grid-template-columns: 1fr 320px;
  gap: 24px;
  padding: 24px;
  max-width: 1400px;
  margin: 0 auto;
}

.video-player {
  background: #000;
  border-radius: 12px;
  overflow: hidden;
}

.video-player video {
  width: 100%;
  height: auto;
  max-height: 70vh;
}

.lesson-sidebar {
  background: var(--bg-primary);
  border-radius: 12px;
  padding: 20px;
  height: fit-content;
}

.lesson-sidebar h3 {
  font-size: 16px;
  margin-bottom: 16px;
}

.lesson-nav-item {
  display: flex;
  align-items: center;
  padding: 12px;
  border-radius: 8px;
  color: var(--text-primary);
  text-decoration: none;
  margin-bottom: 4px;
}

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

.lesson-nav-item.active {
  background: var(--color-primary);
  color: white;
}

.lesson-nav-item.completed::before {
  content: '✓ ';
  color: var(--color-success);
}

/* 我的课程 */
.my-courses-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 24px;
}

.progress-bar {
  height: 6px;
  background: var(--bg-secondary);
  border-radius: 3px;
  margin: 12px 0;
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: var(--color-success);
  border-radius: 3px;
  transition: width 0.3s;
}

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

/* 空状态 */
.empty-state {
  text-align: center;
  padding: 60px 20px;
  color: var(--text-secondary);
}

.empty-state-icon {
  font-size: 64px;
  margin-bottom: 16px;
}

/* 底部 */
.footer {
  background: var(--bg-primary);
  border-top: 1px solid var(--border-color);
  padding: 24px 0;
  text-align: center;
  color: var(--text-secondary);
  margin-top: 60px;
}

/* 提示框 */
.alert {
  padding: 12px 16px;
  border-radius: var(--border-radius);
  margin-bottom: 20px;
}

.alert-error {
  background: #FEE2E2;
  color: #991B1B;
}

.alert-success {
  background: #D1FAE5;
  color: #065F46;
}

/* 响应式 */
@media (max-width: 768px) {
  .hero h1 {
    font-size: 28px;
  }
  
  .courses-grid {
    grid-template-columns: 1fr;
  }
  
  .course-header {
    grid-template-columns: 1fr;
  }
  
  .learn-container {
    grid-template-columns: 1fr;
  }
  
  .nav {
    display: none;
  }
}