/**
 * 2025 现代化模板样式
 * rh888av.com
 * 设计趋势：玻璃态、渐变、微动画、移动端优先
 * SEO优化：结构化数据友好、Core Web Vitals优化
 */

/* ========== CSS变量 - 深色玻璃态主题 ========== */
:root {
    /* 主色调 - 紫蓝渐变 */
    --primary-gradient: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    --primary-color: #667eea;
    --primary-dark: #764ba2;
    
    /* 强调色 */
    --accent-gradient: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);
    --accent-color: #f5576c;
    
    /* 背景色 - 深色玻璃态 */
    --bg-body: #0f0f1a;
    --bg-card: #1a1a2e;
    --bg-header: rgba(26, 26, 46, 0.95);
    --bg-glass: rgba(26, 26, 46, 0.7);
    
    /* 文字色 */
    --text-primary: #e2e8f0;
    --text-secondary: #a0aec0;
    --text-muted: #64748b;
    
    /* 边框和阴影 */
    --border-color: rgba(255, 255, 255, 0.08);
    --border-glass: rgba(255, 255, 255, 0.1);
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.2);
    --shadow-md: 0 4px 20px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 10px 40px rgba(0, 0, 0, 0.4);
    --shadow-glow: 0 0 30px rgba(102, 126, 234, 0.3);
    
    /* 圆角 */
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 20px;
    --radius-xl: 28px;
    
    /* 过渡 */
    --transition-fast: 0.15s ease;
    --transition-normal: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 0.5s cubic-bezier(0.4, 0, 0.2, 1);
}

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

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

body {
    font-family: -apple-system, BlinkMacSystemFont, "SF Pro Display", "Segoe UI", 
                 Roboto, "Helvetica Neue", Arial, "PingFang SC", "Microsoft YaHei", 
                 sans-serif;
    font-size: 15px;
    line-height: 1.7;
    color: var(--text-primary);
    background: var(--bg-body);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    transition: background-color var(--transition-normal), color var(--transition-normal);
}

a {
    text-decoration: none;
    color: inherit;
    transition: color var(--transition-fast);
}

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

img {
    max-width: 100%;
    height: auto;
    display: block;
}

.container {
    max-width: 1440px;
    margin: 0 auto;
    padding: 0 24px;
}

/* ========== 头部导航 - 玻璃态设计 ========== */
.header {
    background: var(--bg-header);
    backdrop-filter: blur(20px) saturate(180%);
    -webkit-backdrop-filter: blur(20px) saturate(180%);
    border-bottom: 1px solid var(--border-glass);
    position: sticky;
    top: 0;
    z-index: 1000;
    transition: all var(--transition-normal);
}

.header-scrolled {
    box-shadow: var(--shadow-md);
}

.header-inner {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 16px 0;
    gap: 32px;
}

.logo {
    flex-shrink: 0;
}

.logo-text {
    font-size: 26px;
    font-weight: 800;
    background: var(--primary-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    letter-spacing: -0.5px;
}

.nav {
    flex: 1;
    display: flex;
    justify-content: center;
}

.nav-list {
    display: flex;
    list-style: none;
    gap: 4px;
}

.nav-item a {
    display: flex;
    align-items: center;
    padding: 10px 18px;
    border-radius: var(--radius-md);
    color: var(--text-secondary);
    font-weight: 500;
    font-size: 15px;
    transition: all var(--transition-fast);
    position: relative;
}

.nav-item a::before {
    content: '';
    position: absolute;
    bottom: 4px;
    left: 50%;
    transform: translateX(-50%) scaleX(0);
    width: 20px;
    height: 3px;
    background: var(--primary-gradient);
    border-radius: 2px;
    transition: transform var(--transition-normal);
}

.nav-item a:hover,
.nav-item.active a {
    color: var(--primary-color);
    background: rgba(102, 126, 234, 0.08);
}

.nav-item a:hover::before,
.nav-item.active a::before {
    transform: translateX(-50%) scaleX(1);
}

/* 搜索框 */
.search-box {
    flex-shrink: 0;
}

.search-box form {
    display: flex;
    gap: 8px;
    align-items: center;
}

.search-box input {
    padding: 10px 18px;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-xl);
    width: 220px;
    background: var(--bg-card);
    font-size: 14px;
    transition: all var(--transition-fast);
}

.search-box input:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(102, 126, 234, 0.1);
    width: 260px;
}

.search-btn {
    padding: 10px 20px;
    background: var(--primary-gradient);
    border: none;
    border-radius: var(--radius-xl);
    color: white;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.search-btn:hover {
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

/* 移动端菜单按钮 */
.mobile-menu-btn {
    display: none;
    background: none;
    border: none;
    color: var(--text-primary);
    cursor: pointer;
    padding: 8px;
    width: 44px;
    height: 44px;
    border-radius: var(--radius-sm);
    transition: background var(--transition-fast);
}

.mobile-menu-btn:hover {
    background: rgba(102, 126, 234, 0.08);
}

.mobile-menu-btn span {
    display: block;
    width: 22px;
    height: 2px;
    background: currentColor;
    margin: 5px auto;
    border-radius: 2px;
    transition: all var(--transition-fast);
}

/* 移动端导航 */
.mobile-nav {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.5);
    backdrop-filter: blur(4px);
    z-index: 2000;
    opacity: 0;
    visibility: hidden;
    transition: all var(--transition-normal);
}

.mobile-nav.active {
    opacity: 1;
    visibility: visible;
}

.mobile-nav-content {
    position: absolute;
    top: 0;
    left: 0;
    width: 300px;
    max-width: 85%;
    height: 100%;
    background: var(--bg-card);
    transform: translateX(-100%);
    transition: transform var(--transition-normal);
    overflow-y: auto;
    -webkit-overflow-scrolling: touch;
}

.mobile-nav.active .mobile-nav-content {
    transform: translateX(0);
}

.mobile-nav ul {
    list-style: none;
    padding: 80px 0 24px;
}

.mobile-nav li {
    border-bottom: 1px solid var(--border-color);
}

.mobile-nav a {
    display: block;
    padding: 16px 24px;
    color: var(--text-primary);
    font-size: 16px;
    font-weight: 500;
    transition: all var(--transition-fast);
}

.mobile-nav a:hover,
.mobile-nav a:active {
    background: rgba(102, 126, 234, 0.08);
    color: var(--primary-color);
    padding-left: 32px;
}

/* ========== Hero Banner - 渐变背景 ========== */
.banner {
    background: var(--primary-gradient);
    position: relative;
    overflow: hidden;
    padding: 80px 0;
}

.banner::before {
    content: '';
    position: absolute;
    inset: 0;
    background: 
        radial-gradient(circle at 20% 80%, rgba(255, 255, 255, 0.1) 0%, transparent 50%),
        radial-gradient(circle at 80% 20%, rgba(255, 255, 255, 0.1) 0%, transparent 50%);
    animation: gradientShift 15s ease infinite;
}

@keyframes gradientShift {
    0%, 100% { transform: scale(1) rotate(0deg); }
    50% { transform: scale(1.1) rotate(5deg); }
}

.banner-content {
    position: relative;
    text-align: center;
    color: white;
    z-index: 1;
}

.banner-content h1 {
    font-size: 48px;
    font-weight: 800;
    margin-bottom: 16px;
    letter-spacing: -1px;
    text-shadow: 0 2px 20px rgba(0, 0, 0, 0.2);
}

.banner-content p {
    font-size: 20px;
    opacity: 0.95;
    font-weight: 300;
}

/* ========== 区块样式 ========== */
.section {
    padding: 60px 0;
    background: var(--bg-body);
}

.section:nth-child(even) {
    background: var(--bg-card);
}

.section-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 32px;
}

.section-title {
    font-size: 24px;
    font-weight: 700;
    color: var(--text-primary);
    display: flex;
    align-items: center;
    gap: 12px;
}

.title-icon {
    width: 36px;
    height: 36px;
    background: var(--primary-gradient);
    border-radius: var(--radius-sm);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 18px;
    color: white;
    box-shadow: var(--shadow-sm);
}

.section-more {
    display: flex;
    align-items: center;
    gap: 6px;
    color: var(--primary-color);
    font-weight: 500;
    font-size: 14px;
    padding: 8px 16px;
    border-radius: var(--radius-xl);
    transition: all var(--transition-fast);
}

.section-more:hover {
    background: rgba(102, 126, 234, 0.08);
    transform: translateX(4px);
}

/* ========== 视频卡片 - 现代化设计 ========== */
.video-grid {
    display: grid;
    grid-template-columns: repeat(6, 1fr);
    gap: 24px;
}

.video-grid-large {
    grid-template-columns: repeat(4, 1fr);
}

.video-card {
    background: var(--bg-card);
    border-radius: var(--radius-lg);
    overflow: hidden;
    border: 1px solid var(--border-color);
    transition: all var(--transition-normal);
    position: relative;
}

.video-card:hover {
    transform: translateY(-8px);
    box-shadow: var(--shadow-lg);
    border-color: transparent;
}

.video-cover {
    position: relative;
    display: block;
    width: 100%;
    aspect-ratio: 2/3;
    overflow: hidden;
    background: var(--bg-body);
}

.video-cover img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    transition: transform var(--transition-slow);
}

.video-card:hover .video-cover img {
    transform: scale(1.08);
}

.video-overlay {
    position: absolute;
    inset: 0;
    background: linear-gradient(to top, rgba(0, 0, 0, 0.8) 0%, transparent 50%);
    display: flex;
    align-items: center;
    justify-content: center;
    opacity: 0;
    transition: opacity var(--transition-normal);
}

.video-card:hover .video-overlay {
    opacity: 1;
}

.play-icon {
    width: 56px;
    height: 56px;
    background: rgba(255, 255, 255, 0.95);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 20px;
    color: var(--primary-color);
    box-shadow: var(--shadow-md);
    transform: scale(0.8);
    transition: transform var(--transition-normal);
}

.video-card:hover .play-icon {
    transform: scale(1);
}

.vip-tag {
    position: absolute;
    top: 12px;
    right: 12px;
    background: var(--accent-gradient);
    color: white;
    padding: 4px 12px;
    border-radius: var(--radius-sm);
    font-size: 11px;
    font-weight: 700;
    letter-spacing: 0.5px;
    box-shadow: var(--shadow-sm);
    z-index: 10;
}

.video-info {
    padding: 16px;
}

.video-title {
    font-size: 15px;
    font-weight: 600;
    margin-bottom: 8px;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    color: var(--text-primary);
    line-height: 1.4;
}

.video-title a {
    color: inherit;
    display: block;
}

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

.video-desc {
    font-size: 13px;
    color: var(--text-muted);
    margin-bottom: 10px;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
    line-height: 1.5;
}

.video-meta {
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 12px;
    color: var(--text-muted);
}

.video-meta .year {
    padding: 2px 8px;
    background: rgba(102, 126, 234, 0.08);
    border-radius: var(--radius-sm);
    color: var(--primary-color);
    font-weight: 500;
}

.video-meta .score {
    color: var(--accent-color);
    font-weight: 600;
}

/* ========== 分类卡片 ========== */
.category-grid {
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    gap: 20px;
}

.category-card {
    background: var(--primary-gradient);
    color: white;
    padding: 32px 20px;
    border-radius: var(--radius-lg);
    text-align: center;
    transition: all var(--transition-normal);
    position: relative;
    overflow: hidden;
}

.category-card::before {
    content: '';
    position: absolute;
    inset: 0;
    background: linear-gradient(135deg, rgba(255,255,255,0.1) 0%, transparent 50%);
    opacity: 0;
    transition: opacity var(--transition-normal);
}

.category-card:hover {
    transform: translateY(-8px) scale(1.02);
    box-shadow: var(--shadow-lg);
}

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

.category-icon {
    width: 64px;
    height: 64px;
    background: rgba(255, 255, 255, 0.2);
    backdrop-filter: blur(10px);
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 28px;
    margin: 0 auto 16px;
    border: 1px solid rgba(255, 255, 255, 0.3);
}

.category-card h3 {
    font-size: 18px;
    font-weight: 600;
    margin-bottom: 8px;
}

.category-card p {
    font-size: 13px;
    opacity: 0.9;
}

/* ========== 排行榜 ========== */
.ranking-list {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.ranking-item {
    display: flex;
    gap: 16px;
    align-items: center;
    padding: 16px 20px;
    background: var(--bg-card);
    border-radius: var(--radius-md);
    border: 1px solid var(--border-color);
    transition: all var(--transition-fast);
}

.ranking-item:hover {
    transform: translateX(8px);
    box-shadow: var(--shadow-md);
    border-color: var(--primary-color);
}

.ranking-num {
    width: 44px;
    height: 44px;
    background: var(--bg-body);
    border-radius: var(--radius-sm);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 18px;
    font-weight: 700;
    color: var(--text-muted);
    flex-shrink: 0;
}

.ranking-num.top {
    background: var(--accent-gradient);
    color: white;
    box-shadow: var(--shadow-sm);
}

.ranking-info {
    flex: 1;
    min-width: 0;
}

.ranking-info h3 {
    font-size: 15px;
    font-weight: 600;
    margin-bottom: 4px;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.ranking-meta {
    font-size: 13px;
    color: var(--text-muted);
    display: flex;
    gap: 12px;
}

/* ========== 页脚 ========== */
.footer {
    background: linear-gradient(135deg, #1a1a2e 0%, #16213e 100%);
    color: rgba(255, 255, 255, 0.8);
    padding: 60px 0 30px;
    margin-top: 60px;
}

.footer-content {
    text-align: center;
}

.footer-links {
    margin-bottom: 24px;
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
    gap: 8px;
}

.footer-links a {
    display: inline-flex;
    align-items: center;
    padding: 8px 16px;
    color: rgba(255, 255, 255, 0.7);
    border-radius: var(--radius-sm);
    transition: all var(--transition-fast);
}

.footer-links a:hover {
    color: white;
    background: rgba(255, 255, 255, 0.1);
}

.footer-info p {
    margin: 8px 0;
    font-size: 14px;
    line-height: 1.6;
}

.footer-info a {
    color: rgba(255, 255, 255, 0.9);
    text-decoration: underline;
}

.copyright {
    margin-top: 24px;
    padding-top: 24px;
    border-top: 1px solid rgba(255, 255, 255, 0.1);
    font-size: 13px;
    color: rgba(255, 255, 255, 0.5);
}

/* ========== 分页 ========== */
.pagination-container {
    margin-top: 48px;
    text-align: center;
    padding: 20px 0;
}

.pagination {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 8px;
    flex-wrap: wrap;
    margin-bottom: 12px;
}

.pagination a,
.pagination span {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 10px 18px;
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-xl);
    min-width: 44px;
    font-weight: 500;
    font-size: 14px;
    transition: all var(--transition-fast);
    cursor: pointer;
}

.pagination a:hover {
    background: var(--primary-gradient);
    color: white;
    border-color: transparent;
    transform: translateY(-2px);
    box-shadow: var(--shadow-sm);
}

.pagination .current {
    background: var(--primary-gradient);
    color: white;
    border-color: transparent;
    box-shadow: var(--shadow-sm);
    cursor: default;
}

.pagination .page-ellipsis {
    background: transparent;
    border: none;
    color: var(--text-muted);
    padding: 10px 8px;
    cursor: default;
}

.pagination .page-ellipsis:hover {
    background: transparent;
    color: var(--text-muted);
    transform: none;
    box-shadow: none;
}

.pagination .first-page,
.pagination .last-page {
    font-weight: 600;
    background: var(--bg-body);
}

.pagination .prev-page,
.pagination .next-page {
    font-weight: 600;
}

.pagination-info {
    font-size: 13px;
    color: var(--text-muted);
    margin-top: 8px;
}

/* 分页响应式 */
@media (max-width: 768px) {
    .pagination {
        gap: 6px;
    }
    
    .pagination a,
    .pagination span {
        padding: 8px 12px;
        min-width: 36px;
        font-size: 13px;
    }
    
    .pagination .first-page,
    .pagination .last-page {
        display: none;
    }
}

@media (max-width: 480px) {
    .pagination a,
    .pagination span {
        padding: 6px 10px;
        min-width: 32px;
        font-size: 12px;
    }
    
    .pagination .prev-page,
    .pagination .next-page {
        padding: 6px 12px;
    }
}

/* ========== 面包屑 ========== */
.breadcrumb {
    padding: 20px 0;
    font-size: 14px;
    color: var(--text-muted);
    display: flex;
    align-items: center;
    flex-wrap: wrap;
    gap: 8px;
}

.breadcrumb a {
    color: var(--primary-color);
    transition: color var(--transition-fast);
}

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

.breadcrumb .separator {
    color: var(--text-muted);
    opacity: 0.5;
}

.breadcrumb .current {
    color: var(--text-secondary);
}

/* ========== 返回顶部 ========== */
.back-to-top {
    position: fixed;
    right: 24px;
    bottom: 24px;
    width: 48px;
    height: 48px;
    background: var(--primary-gradient);
    color: white;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 20px;
    box-shadow: var(--shadow-md);
    opacity: 0;
    visibility: hidden;
    transform: translateY(20px);
    transition: all var(--transition-normal);
    z-index: 999;
}

.back-to-top.show {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

.back-to-top:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg), var(--shadow-glow);
}

/* ========== 广告样式 ========== */
.ad-section {
    padding: 24px 0;
    background: var(--bg-card);
}

.ad-banner {
    margin: 20px auto;
    text-align: center;
}

.ad-banner-960x80 {
    max-width: 960px;
}

.ad-banner img {
    display: block;
    margin: 0 auto;
}

.ad-code {
    min-height: 80px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.ad-code-cover {
    width: 100%;
    height: 100%;
    min-height: 280px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--bg-body);
    border-radius: var(--radius-md);
}

/* 视频卡片广告 */
.video-card.ad-card {
    padding: 0;
    overflow: hidden;
    border: none;
}

.video-card.ad-card a {
    display: block;
    width: 100%;
    height: 100%;
}

.video-card.ad-card img {
    width: 100%;
    height: 100%;
    object-fit: cover;
}

.video-card.ad-card .video-info,
.video-card.ad-card .video-meta,
.video-card.ad-card .video-title,
.video-card.ad-card p,
.video-card.ad-card div:not(:first-child) {
    display: none;
}

/* 导航栏下方广告 */
.nav-ad-container {
    background: var(--bg-card);
    border-bottom: 1px solid var(--border-color);
    padding: 16px 0;
    text-align: center;
}

.nav-ad-container > div {
    max-width: 960px;
    margin: 0 auto;
}

/* ========== 空状态 ========== */
.empty-state {
    text-align: center;
    padding: 80px 20px;
}

.empty-icon {
    font-size: 72px;
    margin-bottom: 20px;
    opacity: 0.5;
}

.empty-state p {
    font-size: 18px;
    color: var(--text-muted);
}

/* ========== 响应式设计 ========== */

/* 大屏幕 */
@media (max-width: 1400px) {
    .video-grid {
        grid-template-columns: repeat(5, 1fr);
    }
}

/* 平板 */
@media (max-width: 1024px) {
    .video-grid {
        grid-template-columns: repeat(4, 1fr);
        gap: 16px;
    }
    
    .video-grid-large {
        grid-template-columns: repeat(3, 1fr);
    }
    
    .category-grid {
        grid-template-columns: repeat(3, 1fr);
    }
    
    .search-box input {
        width: 180px;
    }
    
    .banner-content h1 {
        font-size: 36px;
    }
    
    .banner-content p {
        font-size: 16px;
    }
}

/* 手机横屏 */
@media (max-width: 768px) {
    .container {
        padding: 0 16px;
    }
    
    .header-inner {
        flex-wrap: wrap;
        gap: 12px;
    }
    
    .nav {
        display: none;
    }
    
    .search-box {
        order: 3;
        width: 100%;
    }
    
    .search-box form {
        width: 100%;
    }
    
    .search-box input {
        flex: 1;
        width: auto;
    }
    
    .mobile-menu-btn {
        display: block;
    }
    
    .mobile-nav {
        display: block;
    }
    
    .video-grid {
        grid-template-columns: repeat(3, 1fr);
        gap: 12px;
    }
    
    .video-grid-large {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .category-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .banner {
        padding: 48px 0;
    }
    
    .banner-content h1 {
        font-size: 28px;
    }
    
    .banner-content p {
        font-size: 15px;
    }
    
    .section {
        padding: 32px 0;
    }
    
    .section-title {
        font-size: 20px;
    }
    
    .footer-links {
        flex-direction: column;
        gap: 4px;
    }
}

/* 手机竖屏 */
@media (max-width: 480px) {
    .video-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: 10px;
    }
    
    .video-card {
        border-radius: var(--radius-md);
    }
    
    .video-info {
        padding: 12px;
    }
    
    .video-title {
        font-size: 13px;
    }
    
    .video-meta {
        font-size: 11px;
    }
    
    .category-grid {
        grid-template-columns: 1fr;
    }
    
    .ranking-item {
        padding: 12px 16px;
    }
    
    .back-to-top {
        right: 16px;
        bottom: 16px;
        width: 44px;
        height: 44px;
    }
}

/* ========== 动画效果 ========== */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.video-card,
.category-card,
.ranking-item {
    animation: fadeInUp 0.5s ease backwards;
}

.video-card:nth-child(1) { animation-delay: 0.05s; }
.video-card:nth-child(2) { animation-delay: 0.1s; }
.video-card:nth-child(3) { animation-delay: 0.15s; }
.video-card:nth-child(4) { animation-delay: 0.2s; }
.video-card:nth-child(5) { animation-delay: 0.25s; }
.video-card:nth-child(6) { animation-delay: 0.3s; }

/* ========== 辅助类 ========== */
.text-center { text-align: center; }
.text-right { text-align: right; }
.mt-10 { margin-top: 10px; }
.mt-20 { margin-top: 20px; }
.mb-10 { margin-bottom: 10px; }
.mb-20 { margin-bottom: 20px; }
.hidden { display: none; }

/* ========== 打印样式 ========== */
@media print {
    .header,
    .footer,
    .back-to-top,
    .mobile-nav {
        display: none !important;
    }
}