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

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Microsoft YaHei", sans-serif;
    line-height: 1.6;
    color: #333;
    background: #fafafa;
}

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

/* Header */
header {
    background: #2c3e50;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
    position: sticky;
    top: 0;
    z-index: 1000;
}

header .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 15px 20px;
}

.simple-header .container {
    justify-content: center;
    position: relative;
}

.logo {
    font-size: 24px;
    font-weight: bold;
    color: #fff;
}

.back-btn {
    position: absolute;
    left: 20px;
    text-decoration: none;
    color: #fff;
    font-size: 16px;
    font-weight: 500;
    transition: color 0.3s;
}

.back-btn:hover {
    color: #3498db;
}

nav a {
    margin-left: 30px;
    text-decoration: none;
    color: #333;
    font-size: 16px;
    transition: color 0.3s;
}

nav a:hover {
    color: #4a90e2;
}

/* Banner Slider */
.banner-slider {
    position: relative;
    width: 100%;
    overflow: hidden;
    background: #000;
}

.slider-container {
    position: relative;
    max-width: 1200px;
    margin: 0 auto;
    height: 400px;
}

.slide {
    display: none;
    width: 100%;
    height: 100%;
}

.slide.active {
    display: block;
}

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

.slider-btn {
    position: absolute;
    top: 50%;
    transform: translateY(-50%);
    background: rgba(0,0,0,0.5);
    color: white;
    border: none;
    padding: 15px 20px;
    font-size: 24px;
    cursor: pointer;
    z-index: 10;
    transition: background 0.3s;
}

.slider-btn:hover {
    background: rgba(0,0,0,0.8);
}

.slider-btn.prev {
    left: 20px;
}

.slider-btn.next {
    right: 20px;
}

.slider-dots {
    position: absolute;
    bottom: 20px;
    left: 50%;
    transform: translateX(-50%);
    display: flex;
    gap: 10px;
    z-index: 10;
}

.dot {
    width: 12px;
    height: 12px;
    border-radius: 50%;
    background: rgba(255,255,255,0.5);
    cursor: pointer;
    transition: background 0.3s;
}

.dot.active {
    background: white;
}

/* Hero Banner */
.hero-banner {
    background: linear-gradient(135deg, #1e3c72 0%, #2a5298 50%, #7e22ce 100%);
    padding: 100px 20px;
    text-align: center;
    color: white;
    position: relative;
    overflow: hidden;
}

.banner-bg {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-image:
        url('https://images.unsplash.com/photo-1517694712202-14dd9538aa97?w=1600&h=600&fit=crop&q=80'),
        linear-gradient(135deg, rgba(30, 60, 114, 0.9) 0%, rgba(42, 82, 152, 0.9) 50%, rgba(126, 34, 206, 0.9) 100%);
    background-size: cover;
    background-position: center;
    background-blend-mode: overlay;
    opacity: 0.95;
}

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

.hero-content h1 {
    font-size: 52px;
    margin-bottom: 20px;
    font-weight: 700;
    text-shadow: 2px 2px 4px rgba(0,0,0,0.3);
}

.hero-content p {
    font-size: 22px;
    opacity: 0.95;
    font-weight: 300;
    margin-bottom: 30px;
}

.hero-features {
    display: flex;
    justify-content: center;
    gap: 40px;
    margin-top: 30px;
}

.feature-item {
    font-size: 18px;
    font-weight: 500;
    color: white;
    background: rgba(255, 255, 255, 0.1);
    padding: 12px 25px;
    border-radius: 25px;
    backdrop-filter: blur(10px);
}

.feature-item span {
    color: #4ade80;
    font-weight: bold;
    margin-right: 8px;
    font-size: 20px;
}

/* Main Content Layout */
.main-content {
    padding: 40px 20px;
    background: #f8f9fa;
}

.content-wrapper {
    display: flex;
    gap: 30px;
    max-width: 1200px;
    margin: 0 auto;
}

/* Sidebar Category */
.sidebar-category {
    width: 250px;
    background: white;
    border-radius: 15px;
    padding: 25px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.08);
    height: fit-content;
    position: sticky;
    top: 80px;
}

.sidebar-category h3 {
    font-size: 20px;
    color: #2c3e50;
    margin-bottom: 20px;
    padding-bottom: 15px;
    border-bottom: 2px solid #e9ecef;
}

.category-list {
    list-style: none;
    padding: 0;
    margin: 0;
}

.category-list .category-item {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 15px;
    margin-bottom: 8px;
    border-radius: 10px;
    cursor: pointer;
    transition: all 0.3s;
    color: #5a6c7d;
    font-size: 16px;
}

.category-list .category-item:hover {
    background: #f8f9fa;
    color: #2c3e50;
    transform: translateX(5px);
}

.category-list .category-item.active {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    font-weight: 600;
}

.category-list .category-icon {
    font-size: 24px;
}

/* Products Area */
.products-area {
    flex: 1;
}

.section-header {
    text-align: center;
    margin-bottom: 40px;
}

.section-header h2 {
    font-size: 32px;
    color: #2c3e50;
    margin-bottom: 10px;
}

.section-header p {
    font-size: 16px;
    color: #7f8c8d;
}

.products-list {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 25px;
}

.product-item {
    background: white;
    border-radius: 15px;
    overflow: hidden;
    box-shadow: 0 4px 15px rgba(0,0,0,0.1);
    transition: all 0.3s;
    display: flex;
    flex-direction: column;
}

.product-item:hover {
    transform: translateY(-8px);
    box-shadow: 0 8px 25px rgba(0,0,0,0.15);
}

.product-image {
    position: relative;
    overflow: hidden;
}

.product-image img {
    width: 100%;
    height: 250px;
    object-fit: cover;
    transition: transform 0.3s;
}

.product-item:hover .product-image img {
    transform: scale(1.05);
}

.product-tag {
    position: absolute;
    top: 15px;
    right: 15px;
    background: #e74c3c;
    color: white;
    padding: 5px 15px;
    border-radius: 20px;
    font-size: 12px;
    font-weight: bold;
}

.product-details {
    padding: 25px;
    flex: 1;
    display: flex;
    flex-direction: column;
}

.product-details h3 {
    font-size: 20px;
    color: #2c3e50;
    margin-bottom: 10px;
}

.product-details p {
    color: #7f8c8d;
    font-size: 14px;
    margin-bottom: 20px;
    flex: 1;
}

.product-footer {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.price-info {
    display: flex;
    flex-direction: column;
}

.price {
    font-size: 28px;
    color: #e74c3c;
    font-weight: bold;
}

.old-price {
    font-size: 16px;
    color: #95a5a6;
    text-decoration: line-through;
}

.btn-detail {
    padding: 10px 25px;
    background: #3498db;
    color: white;
    text-decoration: none;
    border-radius: 25px;
    font-weight: bold;
    transition: all 0.3s;
}

.btn-detail:hover {
    background: #2980b9;
    box-shadow: 0 4px 8px rgba(0,0,0,0.2);
}

/* Hero Section */
.hero {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    padding: 80px 20px;
    text-align: center;
}

.hero h1 {
    font-size: 48px;
    margin-bottom: 20px;
}

.hero p {
    font-size: 20px;
    margin-bottom: 30px;
}

/* Buttons */
.btn {
    display: inline-block;
    padding: 12px 30px;
    background: #e74c3c;
    color: #fff;
    text-decoration: none;
    border-radius: 25px;
    font-weight: bold;
    transition: all 0.3s;
}

.btn:hover {
    background: #c0392b;
    transform: translateY(-2px);
}

.btn-small {
    display: inline-block;
    padding: 8px 20px;
    background: #3498db;
    color: white;
    text-decoration: none;
    border-radius: 20px;
    font-size: 14px;
    transition: all 0.3s;
}

.btn-small:hover {
    background: #2980b9;
    box-shadow: 0 4px 8px rgba(0,0,0,0.2);
}

.btn-buy {
    padding: 15px 40px;
    background: #27ae60;
    color: white;
    border: none;
    border-radius: 25px;
    font-size: 18px;
    font-weight: bold;
    cursor: pointer;
    transition: all 0.3s;
}

.btn-buy:hover {
    background: #229954;
    box-shadow: 0 6px 12px rgba(0,0,0,0.2);
}

/* Features Section */
.features {
    padding: 60px 20px;
    background: white;
}

.features h2 {
    text-align: center;
    font-size: 36px;
    margin-bottom: 40px;
}

.feature-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 30px;
}

.feature-item {
    text-align: center;
    padding: 30px;
    background: #f9f9f9;
    border-radius: 10px;
}

.feature-item h3 {
    font-size: 24px;
    margin-bottom: 15px;
}

/* Course Grid */
.hot-courses, .courses-section {
    padding: 60px 20px;
}

.hot-courses h2, .courses-section h2 {
    text-align: center;
    font-size: 36px;
    margin-bottom: 40px;
}

.course-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 30px;
}

.course-card {
    background: white;
    border-radius: 10px;
    overflow: hidden;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
    transition: transform 0.3s;
}

.course-card:hover {
    transform: translateY(-5px);
}

.course-card img {
    width: 100%;
    height: 200px;
    object-fit: contain;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
}

.course-info {
    padding: 20px;
}

.course-info h3 {
    font-size: 20px;
    margin-bottom: 10px;
}

.course-info p {
    color: #666;
    margin-bottom: 15px;
}

.course-details {
    display: flex;
    gap: 15px;
    margin-bottom: 15px;
    font-size: 14px;
    color: #888;
}

.course-meta {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.price {
    font-size: 24px;
    color: #ff6b6b;
    font-weight: bold;
}

/* Page Header */
.page-header {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    padding: 60px 20px;
    text-align: center;
}

.page-header h1 {
    font-size: 42px;
    margin-bottom: 10px;
}

/* Course Detail */
.course-detail {
    padding: 40px 20px;
}

.detail-header {
    background: white;
    border-radius: 10px;
    padding: 30px;
    margin-bottom: 30px;
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 40px;
    align-items: start;
}

.detail-img {
    width: 100%;
    border-radius: 10px;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    height: 350px;
    object-fit: contain;
}

.detail-info h1 {
    font-size: 32px;
    margin-bottom: 15px;
}

.subtitle {
    color: #666;
    font-size: 18px;
    margin-bottom: 20px;
}

.meta-info {
    display: flex;
    gap: 20px;
    margin-bottom: 20px;
    font-size: 16px;
    color: #888;
}

.price-box {
    margin-bottom: 25px;
}

.current-price {
    font-size: 36px;
    color: #ff6b6b;
    font-weight: bold;
    margin-right: 15px;
}

.original-price {
    font-size: 20px;
    color: #999;
    text-decoration: line-through;
}

.detail-content {
    display: grid;
    grid-template-columns: 2fr 1fr;
    gap: 30px;
}

.content-main {
    background: white;
    border-radius: 10px;
    padding: 30px;
}

.section {
    margin-bottom: 40px;
}

.section h2 {
    font-size: 24px;
    margin-bottom: 20px;
    padding-bottom: 10px;
    border-bottom: 2px solid #4a90e2;
}

.curriculum .chapter {
    margin-bottom: 25px;
}

.curriculum h3 {
    font-size: 18px;
    margin-bottom: 10px;
    color: #4a90e2;
}

.curriculum ul {
    list-style: none;
    padding-left: 20px;
}

.curriculum li {
    padding: 8px 0;
    color: #666;
}

.target-audience {
    list-style: none;
}

.target-audience li {
    padding: 10px 0;
    font-size: 16px;
}

.teacher-info {
    background: #f9f9f9;
    padding: 20px;
    border-radius: 5px;
}

.content-sidebar {
    display: flex;
    flex-direction: column;
    gap: 20px;
}

.sidebar-box {
    background: white;
    border-radius: 10px;
    padding: 25px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

.sidebar-box h3 {
    font-size: 20px;
    margin-bottom: 20px;
    color: #4a90e2;
}

.info-list, .guarantee-list {
    list-style: none;
}

.info-list li, .guarantee-list li {
    padding: 10px 0;
    border-bottom: 1px solid #eee;
}

.info-list li:last-child, .guarantee-list li:last-child {
    border-bottom: none;
}

/* About & Policy Pages */
.about-content, .policy-content {
    padding: 40px 20px;
}

.about-section, .policy-text {
    background: white;
    border-radius: 10px;
    padding: 30px;
    margin-bottom: 30px;
}

.about-section h2, .policy-text h2 {
    font-size: 24px;
    margin-bottom: 20px;
    color: #4a90e2;
}

.advantage-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 25px;
    margin-top: 20px;
}

.advantage-item {
    padding: 20px;
    background: #f9f9f9;
    border-radius: 8px;
}

.advantage-item h3 {
    font-size: 20px;
    margin-bottom: 10px;
}

.contact-info {
    background: #f9f9f9;
    padding: 25px;
    border-radius: 8px;
}

.contact-info p {
    margin-bottom: 15px;
    font-size: 16px;
}

.policy-text ul {
    margin: 15px 0 15px 30px;
}

.policy-text li {
    margin-bottom: 10px;
}

/* Footer */
footer {
    background: #34495e;
    color: white;
    padding: 30px 20px;
    text-align: center;
    margin-top: 60px;
}

footer a {
    color: #3498db;
    text-decoration: none;
    margin: 0 10px;
}

footer a:hover {
    text-decoration: underline;
}

/* Responsive Design */
@media (max-width: 768px) {
    .hero-content h1 {
        font-size: 32px;
    }

    .hero-content p {
        font-size: 16px;
    }

    .content-wrapper {
        flex-direction: column;
    }

    .sidebar-category {
        width: 100%;
        position: static;
    }

    .category-list {
        display: grid;
        grid-template-columns: repeat(2, 1fr);
        gap: 10px;
    }

    .products-list {
        grid-template-columns: 1fr;
    }

    .product-item {
        flex-direction: row;
    }

    .product-image {
        width: 40%;
    }

    .product-image img {
        height: 100%;
    }

    .product-details {
        width: 60%;
    }

    .hero h1 {
        font-size: 32px;
    }

    .hero p {
        font-size: 16px;
    }

    nav a {
        margin-left: 15px;
        font-size: 14px;
    }

    .logo {
        font-size: 20px;
    }

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

    .product-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: 15px;
    }

    .slider-container {
        height: 250px;
    }

    .slider-btn {
        padding: 10px 15px;
        font-size: 18px;
    }

    .detail-header {
        grid-template-columns: 1fr;
    }

    .detail-content {
        grid-template-columns: 1fr;
    }

    .content-sidebar {
        order: -1;
    }

    .page-header h1 {
        font-size: 28px;
    }

    .detail-info h1 {
        font-size: 24px;
    }

    .current-price {
        font-size: 28px;
    }

    .advantage-grid {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 480px) {
    header .container {
        flex-direction: column;
        gap: 15px;
    }

    nav {
        display: flex;
        gap: 10px;
    }

    nav a {
        margin-left: 0;
    }

    .hero {
        padding: 40px 20px;
    }

    .hero h1 {
        font-size: 24px;
    }

    .features h2, .hot-courses h2 {
        font-size: 28px;
    }

    .slider-container {
        height: 200px;
    }

    .slider-btn {
        padding: 8px 12px;
        font-size: 16px;
    }

    .slider-btn.prev {
        left: 10px;
    }

    .slider-btn.next {
        right: 10px;
    }
}