/* ============================================
   糖心vlog - 完全原创CSS设计
   配色方案：深海蓝 + 珊瑚橙 + 暖金
   ============================================ */

/* CSS变量 */
:root {
    --primary-color: #0A1628;
    --primary-light: #132240;
    --secondary-color: #FF6B4A;
    --secondary-hover: #FF8566;
    --accent-color: #FFD166;
    --accent-dim: #E6B84D;
    --text-primary: #E8ECF1;
    --text-secondary: #9BA8B9;
    --text-dark: #2C3E50;
    --bg-primary: #060E1A;
    --bg-secondary: #0D1B2E;
    --bg-card: #111F35;
    --bg-card-hover: #162844;
    --border-color: rgba(255,255,255,0.08);
    --border-radius: 12px;
    --border-radius-sm: 8px;
    --border-radius-lg: 20px;
    --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 8px 40px rgba(0,0,0,0.4);
    --shadow-glow: 0 0 20px rgba(255,107,74,0.15);
    --transition-fast: 0.2s cubic-bezier(0.4,0,0.2,1);
    --transition-normal: 0.35s cubic-bezier(0.4,0,0.2,1);
    --max-width: 1280px;
    --nav-height: 72px;
}

/* 全局重置 */
*, *::before, *::after {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
    font-size: 16px;
    -webkit-text-size-adjust: 100%;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Helvetica Neue", Arial, sans-serif;
    background-color: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.7;
    overflow-x: hidden;
    -webkit-font-smoothing: antialiased;
}

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

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

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

ul, ol {
    list-style: none;
}

.container {
    width: 100%;
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 0 24px;
}

/* ============================================
   导航栏
   ============================================ */
.site-nav {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: var(--nav-height);
    background: rgba(6,14,26,0.92);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border-bottom: 1px solid var(--border-color);
    z-index: 1000;
    transition: background var(--transition-normal);
}

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

.nav-logo {
    display: flex;
    align-items: center;
    gap: 10px;
    flex-shrink: 0;
}

.nav-logo img {
    height: 40px;
    width: 40px;
    border-radius: 8px;
}

.nav-logo span {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--text-primary);
    letter-spacing: -0.02em;
}

.nav-logo span em {
    font-style: normal;
    color: var(--secondary-color);
}

.nav-menu {
    display: flex;
    align-items: center;
    gap: 4px;
}

.nav-menu a {
    color: var(--text-secondary);
    font-size: 0.9rem;
    font-weight: 500;
    padding: 8px 14px;
    border-radius: var(--border-radius-sm);
    transition: all var(--transition-fast);
    white-space: nowrap;
}

.nav-menu a:hover,
.nav-menu a.active {
    color: var(--text-primary);
    background: rgba(255,107,74,0.1);
}

.nav-download {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    background: linear-gradient(135deg, var(--secondary-color), #FF8566);
    color: #fff !important;
    font-size: 0.875rem;
    font-weight: 600;
    padding: 10px 20px;
    border-radius: 50px;
    transition: all var(--transition-fast);
    box-shadow: 0 2px 12px rgba(255,107,74,0.3);
}

.nav-download:hover {
    transform: translateY(-1px);
    box-shadow: 0 4px 20px rgba(255,107,74,0.4);
    color: #fff !important;
}

/* 移动端菜单按钮 */
.menu-toggle {
    display: none;
    flex-direction: column;
    gap: 5px;
    background: none;
    border: none;
    cursor: pointer;
    padding: 8px;
}

.menu-toggle span {
    display: block;
    width: 24px;
    height: 2px;
    background: var(--text-primary);
    border-radius: 2px;
    transition: all var(--transition-fast);
}

.menu-toggle.active span:nth-child(1) {
    transform: rotate(45deg) translate(5px, 5px);
}

.menu-toggle.active span:nth-child(2) {
    opacity: 0;
}

.menu-toggle.active span:nth-child(3) {
    transform: rotate(-45deg) translate(5px, -5px);
}

/* ============================================
   Hero / 欢迎区域
   ============================================ */
.hero-section {
    position: relative;
    min-height: 85vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: calc(var(--nav-height) + 40px) 24px 60px;
    overflow: hidden;
}

.hero-bg {
    position: absolute;
    inset: 0;
    z-index: 0;
}

.hero-bg img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    opacity: 0.35;
}

.hero-bg::after {
    content: '';
    position: absolute;
    inset: 0;
    background: linear-gradient(180deg, rgba(6,14,26,0.6) 0%, rgba(6,14,26,0.95) 100%);
}

.hero-content {
    position: relative;
    z-index: 1;
    text-align: center;
    max-width: 720px;
}

.hero-content h1 {
    font-size: 3rem;
    font-weight: 800;
    line-height: 1.2;
    margin-bottom: 20px;
    background: linear-gradient(135deg, var(--text-primary) 0%, var(--accent-color) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero-content .hero-desc {
    font-size: 1.1rem;
    color: var(--text-secondary);
    line-height: 1.8;
    margin-bottom: 32px;
}

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

.btn-primary {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    background: linear-gradient(135deg, var(--secondary-color), #FF8566);
    color: #fff;
    font-size: 1rem;
    font-weight: 600;
    padding: 14px 32px;
    border-radius: 50px;
    border: none;
    cursor: pointer;
    transition: all var(--transition-fast);
    box-shadow: 0 4px 20px rgba(255,107,74,0.3);
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 28px rgba(255,107,74,0.45);
    color: #fff;
}

.btn-outline {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    background: transparent;
    color: var(--text-primary);
    font-size: 1rem;
    font-weight: 600;
    padding: 14px 32px;
    border-radius: 50px;
    border: 2px solid var(--border-color);
    cursor: pointer;
    transition: all var(--transition-fast);
}

.btn-outline:hover {
    border-color: var(--secondary-color);
    color: var(--secondary-color);
    background: rgba(255,107,74,0.05);
}

/* ============================================
   通用区块样式
   ============================================ */
.section {
    padding: 80px 0;
}

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

.section-title {
    font-size: 2rem;
    font-weight: 700;
    text-align: center;
    margin-bottom: 12px;
    color: var(--text-primary);
}

.section-subtitle {
    font-size: 1rem;
    color: var(--text-secondary);
    text-align: center;
    margin-bottom: 48px;
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
}

/* ============================================
   精选视频区
   ============================================ */
.featured-video {
    position: relative;
    border-radius: var(--border-radius-lg);
    overflow: hidden;
    max-width: 900px;
    margin: 0 auto 32px;
    box-shadow: var(--shadow-lg);
}

.featured-video img {
    width: 100%;
    aspect-ratio: 16/9;
    object-fit: cover;
}

.featured-video .play-overlay {
    position: absolute;
    inset: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    background: rgba(0,0,0,0.3);
    transition: background var(--transition-fast);
    cursor: pointer;
}

.featured-video .play-overlay:hover {
    background: rgba(0,0,0,0.15);
}

.play-btn {
    width: 72px;
    height: 72px;
    background: var(--secondary-color);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: 0 4px 24px rgba(255,107,74,0.4);
    transition: transform var(--transition-fast);
}

.play-btn::after {
    content: '';
    display: block;
    width: 0;
    height: 0;
    border-style: solid;
    border-width: 12px 0 12px 22px;
    border-color: transparent transparent transparent #fff;
    margin-left: 4px;
}

.featured-video:hover .play-btn {
    transform: scale(1.1);
}

.featured-desc {
    text-align: center;
    font-size: 1rem;
    color: var(--text-secondary);
    max-width: 700px;
    margin: 0 auto;
    line-height: 1.8;
}

/* ============================================
   关于我们
   ============================================ */
.about-content {
    max-width: 800px;
    margin: 0 auto;
    font-size: 1rem;
    line-height: 1.9;
    color: var(--text-secondary);
}

.about-content p {
    margin-bottom: 16px;
}

.about-stats {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 24px;
    margin-top: 40px;
}

.stat-item {
    text-align: center;
    padding: 24px 16px;
    background: var(--bg-card);
    border-radius: var(--border-radius);
    border: 1px solid var(--border-color);
}

.stat-number {
    font-size: 2rem;
    font-weight: 800;
    color: var(--secondary-color);
    display: block;
}

.stat-label {
    font-size: 0.875rem;
    color: var(--text-secondary);
    margin-top: 4px;
}

/* ============================================
   视频卡片网格
   ============================================ */
.video-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 24px;
}

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

.video-card:hover {
    transform: translateY(-6px);
    border-color: rgba(255,107,74,0.3);
    box-shadow: var(--shadow-glow);
    background: var(--bg-card-hover);
}

.video-card .card-thumb {
    position: relative;
    aspect-ratio: 16/10;
    overflow: hidden;
}

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

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

.card-thumb .card-badge {
    position: absolute;
    top: 10px;
    left: 10px;
    background: var(--secondary-color);
    color: #fff;
    font-size: 0.75rem;
    font-weight: 600;
    padding: 3px 10px;
    border-radius: 20px;
}

.card-thumb .card-duration {
    position: absolute;
    bottom: 10px;
    right: 10px;
    background: rgba(0,0,0,0.75);
    color: #fff;
    font-size: 0.75rem;
    padding: 2px 8px;
    border-radius: 4px;
}

.video-card .card-body {
    padding: 16px;
}

.video-card .card-title {
    font-size: 0.95rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 8px;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
    line-height: 1.4;
}

.video-meta {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 8px;
}

.video-meta .rating {
    color: var(--accent-color);
    font-size: 0.8rem;
    font-weight: 600;
}

.video-meta .views {
    color: var(--text-secondary);
    font-size: 0.8rem;
}

.video-card .card-desc {
    font-size: 0.825rem;
    color: var(--text-secondary);
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
    line-height: 1.5;
}

/* ============================================
   资质与合规
   ============================================ */
.credential-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 24px;
}

.credential-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    padding: 32px 24px;
    text-align: center;
    transition: all var(--transition-fast);
}

.credential-card:hover {
    border-color: rgba(255,107,74,0.3);
    transform: translateY(-3px);
}

.credential-icon {
    width: 56px;
    height: 56px;
    margin: 0 auto 16px;
    background: linear-gradient(135deg, rgba(255,107,74,0.15), rgba(255,209,102,0.1));
    border-radius: 16px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.5rem;
}

.credential-card h3 {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 8px;
}

.credential-card p {
    font-size: 0.85rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

/* ============================================
   支付方式
   ============================================ */
.payment-icons {
    display: flex;
    justify-content: center;
    gap: 32px;
    flex-wrap: wrap;
}

.payment-item {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 8px;
    padding: 20px 28px;
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    transition: all var(--transition-fast);
    min-width: 120px;
}

.payment-item:hover {
    border-color: rgba(255,107,74,0.3);
    transform: translateY(-2px);
}

.payment-item .pay-icon {
    font-size: 2rem;
}

.payment-item .pay-name {
    font-size: 0.85rem;
    color: var(--text-secondary);
    font-weight: 500;
}

/* ============================================
   客户支持
   ============================================ */
.support-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 24px;
    max-width: 900px;
    margin: 0 auto;
}

.support-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    padding: 32px 24px;
    text-align: center;
}

.support-card .support-icon {
    font-size: 2rem;
    margin-bottom: 12px;
}

.support-card h3 {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 8px;
}

.support-card p {
    font-size: 0.875rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

/* ============================================
   负责任观影
   ============================================ */
.responsible-content {
    max-width: 800px;
    margin: 0 auto;
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-lg);
    padding: 40px;
}

.responsible-content h3 {
    font-size: 1.1rem;
    color: var(--secondary-color);
    margin-bottom: 12px;
    font-weight: 600;
}

.responsible-content p {
    font-size: 0.95rem;
    color: var(--text-secondary);
    line-height: 1.8;
    margin-bottom: 20px;
}

.responsible-content p:last-child {
    margin-bottom: 0;
}

.age-badge {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    background: rgba(255,107,74,0.1);
    border: 1px solid rgba(255,107,74,0.3);
    color: var(--secondary-color);
    font-weight: 700;
    font-size: 1rem;
    padding: 8px 20px;
    border-radius: 50px;
    margin-bottom: 16px;
}

/* ============================================
   FAQ 手风琴
   ============================================ */
.faq-list {
    max-width: 800px;
    margin: 0 auto;
}

.faq-item {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    margin-bottom: 12px;
    overflow: hidden;
    transition: border-color var(--transition-fast);
}

.faq-item.active {
    border-color: rgba(255,107,74,0.3);
}

.faq-question {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 20px 24px;
    cursor: pointer;
    user-select: none;
    transition: background var(--transition-fast);
}

.faq-question:hover {
    background: rgba(255,255,255,0.02);
}

.faq-question h3 {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
    flex: 1;
    padding-right: 16px;
}

.faq-toggle {
    width: 28px;
    height: 28px;
    border-radius: 50%;
    background: rgba(255,107,74,0.1);
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
    transition: all var(--transition-fast);
}

.faq-toggle::after {
    content: '+';
    color: var(--secondary-color);
    font-size: 1.2rem;
    font-weight: 600;
    line-height: 1;
}

.faq-item.active .faq-toggle {
    background: var(--secondary-color);
    transform: rotate(45deg);
}

.faq-item.active .faq-toggle::after {
    color: #fff;
}

.faq-answer {
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.4s ease;
}

.faq-answer-inner {
    padding: 0 24px 20px;
    font-size: 0.925rem;
    color: var(--text-secondary);
    line-height: 1.8;
}

/* ============================================
   用户评价
   ============================================ */
.review-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 24px;
}

.review-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    padding: 24px;
    transition: all var(--transition-fast);
}

.review-card:hover {
    border-color: rgba(255,107,74,0.2);
    transform: translateY(-3px);
}

.review-header {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 12px;
}

.review-avatar {
    width: 44px;
    height: 44px;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--secondary-color), var(--accent-color));
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.1rem;
    font-weight: 700;
    color: #fff;
    flex-shrink: 0;
}

.review-info .review-name {
    font-size: 0.95rem;
    font-weight: 600;
    color: var(--text-primary);
}

.review-info .review-location {
    font-size: 0.8rem;
    color: var(--text-secondary);
}

.review-stars {
    color: var(--accent-color);
    font-size: 0.85rem;
    margin-bottom: 10px;
    letter-spacing: 2px;
}

.review-text {
    font-size: 0.9rem;
    color: var(--text-secondary);
    line-height: 1.7;
    margin-bottom: 10px;
}

.review-date {
    font-size: 0.78rem;
    color: rgba(155,168,185,0.6);
}

/* ============================================
   热门标签
   ============================================ */
.tag-cloud {
    display: flex;
    flex-wrap: wrap;
    gap: 12px;
    justify-content: center;
    max-width: 900px;
    margin: 0 auto;
}

.tag-cloud a {
    display: inline-block;
    padding: 8px 20px;
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 50px;
    color: var(--text-secondary);
    font-size: 0.875rem;
    font-weight: 500;
    transition: all var(--transition-fast);
}

.tag-cloud a:hover {
    background: rgba(255,107,74,0.1);
    border-color: rgba(255,107,74,0.4);
    color: var(--secondary-color);
    transform: translateY(-2px);
}

/* ============================================
   页脚
   ============================================ */
.site-footer {
    background: var(--primary-color);
    border-top: 1px solid var(--border-color);
    padding: 60px 0 0;
}

.footer-grid {
    display: grid;
    grid-template-columns: 2fr 1fr 1fr 1fr;
    gap: 40px;
    margin-bottom: 40px;
}

.footer-brand p {
    font-size: 0.9rem;
    color: var(--text-secondary);
    line-height: 1.7;
    margin-top: 12px;
}

.footer-col h4 {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 16px;
}

.footer-col a {
    display: block;
    font-size: 0.875rem;
    color: var(--text-secondary);
    padding: 4px 0;
    transition: color var(--transition-fast);
}

.footer-col a:hover {
    color: var(--secondary-color);
}

.footer-bottom {
    border-top: 1px solid var(--border-color);
    padding: 24px 0;
    text-align: center;
}

.footer-bottom p {
    font-size: 0.8rem;
    color: rgba(155,168,185,0.5);
    margin-bottom: 4px;
}

/* ============================================
   面包屑导航
   ============================================ */
.breadcrumb {
    padding: calc(var(--nav-height) + 24px) 0 0;
}

.breadcrumb-list {
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 0.875rem;
}

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

.breadcrumb-list a:hover {
    color: var(--secondary-color);
}

.breadcrumb-list .separator {
    color: rgba(155,168,185,0.4);
}

.breadcrumb-list .current {
    color: var(--text-primary);
    font-weight: 500;
}

/* ============================================
   分类页头部
   ============================================ */
.category-header {
    padding: 40px 0 32px;
    text-align: center;
}

.category-header h1 {
    font-size: 2.5rem;
    font-weight: 800;
    color: var(--text-primary);
    margin-bottom: 12px;
}

.category-header .cat-subtitle {
    font-size: 1.05rem;
    color: var(--text-secondary);
}

/* ============================================
   分类页文章
   ============================================ */
.article-content {
    max-width: 860px;
    margin: 0 auto;
    padding: 40px 0 60px;
}

.article-content h2 {
    font-size: 1.6rem;
    font-weight: 700;
    color: var(--text-primary);
    margin: 40px 0 16px;
    padding-left: 16px;
    border-left: 4px solid var(--secondary-color);
}

.article-content h3 {
    font-size: 1.2rem;
    font-weight: 600;
    color: var(--text-primary);
    margin: 28px 0 12px;
}

.article-content p {
    font-size: 1rem;
    color: var(--text-secondary);
    line-height: 1.9;
    margin-bottom: 16px;
}

.article-content img {
    border-radius: var(--border-radius);
    margin: 24px 0;
    box-shadow: var(--shadow-md);
}

.article-content a {
    color: var(--secondary-color);
    border-bottom: 1px solid rgba(255,107,74,0.3);
}

.article-content a:hover {
    border-bottom-color: var(--secondary-color);
}

/* ============================================
   下载页
   ============================================ */
.download-hero {
    padding: calc(var(--nav-height) + 60px) 0 60px;
    text-align: center;
}

.download-hero h1 {
    font-size: 2.5rem;
    font-weight: 800;
    margin-bottom: 16px;
}

.download-hero p {
    font-size: 1.1rem;
    color: var(--text-secondary);
    max-width: 600px;
    margin: 0 auto 32px;
}

.download-buttons {
    display: flex;
    gap: 16px;
    justify-content: center;
    flex-wrap: wrap;
    margin-bottom: 48px;
}

.download-mockup {
    max-width: 360px;
    margin: 0 auto;
}

.download-mockup img {
    border-radius: var(--border-radius-lg);
    box-shadow: var(--shadow-lg);
}

.download-features {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 24px;
    max-width: 900px;
    margin: 60px auto 0;
}

.dl-feature {
    text-align: center;
    padding: 24px;
}

.dl-feature .dl-icon {
    font-size: 2rem;
    margin-bottom: 12px;
}

.dl-feature h3 {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 8px;
}

.dl-feature p {
    font-size: 0.875rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

/* ============================================
   返回顶部
   ============================================ */
.back-to-top {
    position: fixed;
    bottom: 32px;
    right: 32px;
    width: 48px;
    height: 48px;
    background: var(--secondary-color);
    color: #fff;
    border: none;
    border-radius: 50%;
    cursor: pointer;
    font-size: 1.2rem;
    display: flex;
    align-items: center;
    justify-content: center;
    opacity: 0;
    visibility: hidden;
    transform: translateY(20px);
    transition: all var(--transition-fast);
    box-shadow: 0 4px 16px rgba(255,107,74,0.3);
    z-index: 999;
}

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

.back-to-top:hover {
    transform: translateY(-3px);
    box-shadow: 0 6px 24px rgba(255,107,74,0.45);
}

/* ============================================
   响应式设计
   ============================================ */
@media (max-width: 1200px) {
    .video-grid {
        grid-template-columns: repeat(3, 1fr);
    }
    
    .footer-grid {
        grid-template-columns: 1fr 1fr;
    }
}

@media (max-width: 992px) {
    .credential-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .about-stats {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .review-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 768px) {
    :root {
        --nav-height: 64px;
    }
    
    .menu-toggle {
        display: flex;
    }
    
    .nav-menu {
        position: fixed;
        top: var(--nav-height);
        left: 0;
        right: 0;
        bottom: 0;
        background: rgba(6,14,26,0.98);
        flex-direction: column;
        padding: 24px;
        gap: 4px;
        transform: translateX(100%);
        transition: transform var(--transition-normal);
        overflow-y: auto;
    }
    
    .nav-menu.open {
        transform: translateX(0);
    }
    
    .nav-menu a {
        font-size: 1.1rem;
        padding: 14px 16px;
        width: 100%;
    }
    
    .nav-download {
        display: none;
    }
    
    .hero-content h1 {
        font-size: 2rem;
    }
    
    .hero-section {
        min-height: 70vh;
    }
    
    .section {
        padding: 50px 0;
    }
    
    .section-title {
        font-size: 1.6rem;
    }
    
    .video-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: 16px;
    }
    
    .credential-grid {
        grid-template-columns: 1fr;
    }
    
    .support-grid {
        grid-template-columns: 1fr;
    }
    
    .review-grid {
        grid-template-columns: 1fr;
    }
    
    .footer-grid {
        grid-template-columns: 1fr;
        gap: 24px;
    }
    
    .payment-icons {
        gap: 16px;
    }
    
    .payment-item {
        min-width: 100px;
        padding: 16px 20px;
    }
    
    .category-header h1 {
        font-size: 1.8rem;
    }
    
    .download-features {
        grid-template-columns: 1fr;
    }
    
    .responsible-content {
        padding: 24px;
    }
    
    .about-stats {
        grid-template-columns: repeat(2, 1fr);
        gap: 12px;
    }
    
    .hero-actions {
        flex-direction: column;
        align-items: center;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 16px;
    }
    
    .video-grid {
        grid-template-columns: 1fr;
    }
    
    .hero-content h1 {
        font-size: 1.6rem;
    }
    
    .section-title {
        font-size: 1.4rem;
    }
    
    .about-stats {
        grid-template-columns: 1fr 1fr;
    }
}