/* Reset & Base Styles */
:root {
    --primary-color: #ff6b00; /* 活力橙 */
    --secondary-color: #00a8ff; /* 科技蓝 */
    --dark-bg: #1a1a1a;
    --light-text: #f5f5f5;
    --card-bg: #2a2a2a;
    --transition: all 0.3s ease;
}

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

body {
    font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
    background-color: var(--dark-bg);
    color: var(--light-text);
    line-height: 1.6;
}

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

ul {
    list-style: none;
}

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

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

/* Header */
.site-header {
    background-color: rgba(26, 26, 26, 0.95);
    padding: 15px 0;
    position: sticky;
    top: 0;
    z-index: 1000;
    border-bottom: 1px solid #333;
}

.site-header .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo img {
    height: 50px;
}

.main-nav ul {
    display: flex;
    gap: 30px;
}

.main-nav a {
    font-weight: bold;
    font-size: 16px;
}

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

/* Hero Section */
.hero-section {
    height: 600px;
    background-size: cover;
    background-position: center;
    display: flex;
    align-items: center;
    text-align: center;
    position: relative;
}

.hero-section::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.6);
}

.hero-section .container {
    position: relative;
    z-index: 1;
}

.hero-section h1 {
    font-size: 48px;
    margin-bottom: 20px;
    color: #fff;
}

.hero-section p {
    font-size: 20px;
    margin-bottom: 40px;
    color: #ddd;
}

.cta-buttons .btn {
    display: inline-block;
    padding: 12px 30px;
    border-radius: 30px;
    font-weight: bold;
    margin: 0 10px;
}

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

.btn-primary:hover {
    background-color: #e65c00;
}

.btn-secondary {
    background-color: transparent;
    border: 2px solid #fff;
    color: #fff;
}

.btn-secondary:hover {
    background-color: #fff;
    color: var(--dark-bg);
}

/* Sections */
section {
    padding: 80px 0;
}

.section-title {
    text-align: center;
    font-size: 36px;
    margin-bottom: 10px;
    color: var(--primary-color);
}

.section-subtitle {
    text-align: center;
    color: #888;
    margin-bottom: 50px;
}

/* Video Grid */
.video-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 30px;
}

.video-card {
    background-color: var(--card-bg);
    border-radius: 10px;
    overflow: hidden;
    transition: var(--transition);
    position: relative;
}

.video-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 10px 20px rgba(0,0,0,0.3);
}

.video-thumbnail {
    position: relative;
    height: 180px;
    background-color: #000;
    overflow: hidden;
}

.video-thumbnail img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    opacity: 0.8;
    transition: var(--transition);
}

.video-card:hover .video-thumbnail img {
    opacity: 1;
    transform: scale(1.05);
}

.play-icon {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    font-size: 40px;
    color: #fff;
    opacity: 0.8;
    transition: var(--transition);
}

.video-card:hover .play-icon {
    opacity: 1;
    transform: translate(-50%, -50%) scale(1.2);
}

.video-info {
    padding: 15px;
}

.video-title {
    font-size: 16px;
    margin-bottom: 8px;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.video-meta {
    font-size: 12px;
    color: #888;
    display: flex;
    justify-content: space-between;
}

/* Features */
.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 30px;
}

.feature-card {
    background-color: var(--card-bg);
    padding: 30px;
    border-radius: 10px;
    text-align: center;
    transition: var(--transition);
}

.feature-card:hover {
    background-color: #333;
}

.feature-card img {
    height: 150px;
    margin: 0 auto 20px;
    border-radius: 8px;
}

.feature-card h3 {
    margin-bottom: 15px;
    color: var(--secondary-color);
}

/* Experts */
.experts-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 30px;
}

.expert-card {
    text-align: center;
    background: var(--card-bg);
    padding: 20px;
    border-radius: 10px;
}

.expert-avatar {
    width: 100px;
    height: 100px;
    border-radius: 50%;
    margin: 0 auto 15px;
    background-color: #444;
    overflow: hidden;
}

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

/* Footer */
.site-footer {
    background-color: #111;
    padding: 60px 0 20px;
    margin-top: 60px;
}

.footer-content {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 40px;
    margin-bottom: 40px;
}

.footer-brand img {
    height: 40px;
    margin-bottom: 15px;
}

.footer-links ul li {
    margin-bottom: 10px;
}

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

.copyright {
    text-align: center;
    padding-top: 20px;
    border-top: 1px solid #333;
    color: #666;
}

/* Mobile Menu */
.mobile-menu-toggle {
    display: none;
    flex-direction: column;
    gap: 5px;
    cursor: pointer;
}

.mobile-menu-toggle span {
    width: 25px;
    height: 3px;
    background-color: #fff;
    transition: var(--transition);
}

/* Responsive */
@media (max-width: 768px) {
    .hero-section h1 {
        font-size: 32px;
    }
    
    .mobile-menu-toggle {
        display: flex;
    }
    
    .main-nav {
        display: none;
        position: absolute;
        top: 100%;
        left: 0;
        width: 100%;
        background-color: rgba(26, 26, 26, 0.98);
        padding: 20px;
    }
    
    .main-nav.active {
        display: block;
    }
    
    .main-nav ul {
        flex-direction: column;
        gap: 15px;
        text-align: center;
    }
}