* {
    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: #f5f5f5;
}

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

/* Header */
header {
    background: #fff;
    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: #4a90e2;
}

.back-btn {
    position: absolute;
    left: 20px;
    text-decoration: none;
    color: #4a90e2;
    font-size: 16px;
    font-weight: 500;
    transition: color 0.3s;
}

.back-btn:hover {
    color: #357abd;
}

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;
}

/* Course Grid for Home Page */
.course-grid-home {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 30px;
    max-width: 900px;
    margin: 0 auto;
}

/* 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: #fff;
    color: #667eea;
    text-decoration: none;
    border-radius: 5px;
    font-weight: bold;
    transition: transform 0.3s;
}

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

.btn-small {
    display: inline-block;
    padding: 8px 20px;
    background: #4a90e2;
    color: white;
    text-decoration: none;
    border-radius: 5px;
    font-size: 14px;
    transition: background 0.3s;
}

.btn-small:hover {
    background: #357abd;
}

.btn-buy {
    padding: 15px 40px;
    background: #ff6b6b;
    color: white;
    border: none;
    border-radius: 5px;
    font-size: 18px;
    font-weight: bold;
    cursor: pointer;
    transition: background 0.3s;
}

.btn-buy:hover {
    background: #ee5a52;
}

/* 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;
}

/* Platform Features */
.platform-features {
    padding: 60px 20px;
    background: white;
}

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

.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 30px;
    max-width: 1000px;
    margin: 0 auto;
}

.feature-icon {
    font-size: 48px;
    margin-bottom: 15px;
}

/* Student Reviews */
.student-reviews {
    padding: 60px 20px;
    background: #f9f9f9;
}

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

.reviews-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 30px;
    max-width: 1000px;
    margin: 0 auto;
}

.review-card {
    background: white;
    padding: 30px;
    border-radius: 10px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

.review-text {
    font-size: 16px;
    line-height: 1.8;
    color: #666;
    margin-bottom: 20px;
    font-style: italic;
}

.review-author {
    font-size: 14px;
    color: #4a90e2;
    font-weight: 500;
}

/* Footer */
footer {
    background: #2c3e50;
    color: white;
    padding: 30px 20px;
    text-align: center;
    margin-top: 60px;
}

footer a {
    color: white;
    text-decoration: none;
    margin: 0 10px;
}

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

/* About Section */
.about-section {
    padding: 40px 20px;
}

.about-section h1 {
    text-align: center;
    font-size: 36px;
    margin-bottom: 40px;
}

.about-content {
    max-width: 900px;
    margin: 0 auto;
}

.advantage-list {
    list-style: none;
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 25px;
    margin-top: 20px;
}

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

.advantage-list strong {
    display: block;
    font-size: 18px;
    color: #4a90e2;
    margin-bottom: 10px;
}

/* Contact Section */
.contact-section {
    padding: 40px 20px;
}

.contact-section h1 {
    text-align: center;
    font-size: 36px;
    margin-bottom: 40px;
}

.contact-content {
    max-width: 900px;
    margin: 0 auto;
}

.contact-list {
    list-style: none;
    font-size: 16px;
}

.contact-list li {
    padding: 15px 0;
    border-bottom: 1px solid #eee;
}

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

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

/* Learning Center */
.learning-center {
    padding: 40px 20px;
}

.learning-center h1 {
    text-align: center;
    font-size: 36px;
    margin-bottom: 10px;
}

.learning-center .subtitle {
    text-align: center;
    color: #666;
    margin-bottom: 40px;
}

.my-courses {
    max-width: 900px;
    margin: 0 auto 60px;
}

.course-item {
    background: white;
    border-radius: 10px;
    padding: 20px;
    margin-bottom: 20px;
    display: flex;
    gap: 20px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

.course-item img {
    width: 200px;
    height: 120px;
    object-fit: cover;
    border-radius: 8px;
}

.course-progress {
    flex: 1;
}

.course-progress h3 {
    font-size: 20px;
    margin-bottom: 15px;
}

.progress-bar {
    width: 100%;
    height: 10px;
    background: #eee;
    border-radius: 5px;
    overflow: hidden;
    margin-bottom: 10px;
}

.progress {
    height: 100%;
    background: #4a90e2;
    transition: width 0.3s;
}

.btn-continue {
    padding: 10px 25px;
    background: #4a90e2;
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    margin-top: 15px;
}

.learning-features {
    max-width: 900px;
    margin: 0 auto;
}

.learning-features h2 {
    text-align: center;
    font-size: 28px;
    margin-bottom: 30px;
}

.feature-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 20px;
}

.feature-card {
    background: white;
    padding: 25px;
    border-radius: 10px;
    text-align: center;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

.feature-card h3 {
    font-size: 18px;
    margin-bottom: 10px;
}

/* Order Section */
.order-section {
    padding: 40px 20px;
}

.order-section h1 {
    text-align: center;
    font-size: 36px;
    margin-bottom: 40px;
}

.order-content {
    max-width: 700px;
    margin: 0 auto;
}

.order-info, .order-summary, .payment-method {
    background: white;
    border-radius: 10px;
    padding: 25px;
    margin-bottom: 20px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

.order-info h2, .order-summary h2, .payment-method h2 {
    font-size: 20px;
    margin-bottom: 20px;
    color: #4a90e2;
}

.order-course {
    display: flex;
    gap: 20px;
    align-items: center;
}

.order-course img {
    width: 120px;
    height: 80px;
    object-fit: cover;
    border-radius: 8px;
}

.course-detail h3 {
    font-size: 18px;
    margin-bottom: 5px;
}

.summary-list {
    list-style: none;
}

.summary-list li {
    display: flex;
    justify-content: space-between;
    padding: 15px 0;
    border-bottom: 1px solid #eee;
}

.summary-list li.total {
    border-bottom: none;
    font-size: 20px;
    font-weight: bold;
    color: #ff6b6b;
}

.payment-options {
    display: flex;
    gap: 20px;
}

.payment-option {
    flex: 1;
    padding: 15px;
    border: 2px solid #eee;
    border-radius: 8px;
    cursor: pointer;
    transition: border-color 0.3s;
}

.payment-option:has(input:checked) {
    border-color: #4a90e2;
    background: #f0f7ff;
}

.payment-option input {
    margin-right: 10px;
}

.order-actions {
    text-align: center;
    margin-top: 30px;
}

.btn-submit {
    padding: 15px 60px;
    background: #ff6b6b;
    color: white;
    border: none;
    border-radius: 5px;
    font-size: 18px;
    font-weight: bold;
    cursor: pointer;
    transition: background 0.3s;
}

.btn-submit:hover {
    background: #ee5a52;
}

.order-tips {
    margin-top: 15px;
    color: #666;
    font-size: 14px;
}

/* Terms Section */
.terms-section {
    padding: 40px 20px;
}

.terms-section h1 {
    text-align: center;
    font-size: 36px;
    margin-bottom: 10px;
}

.update-time {
    text-align: center;
    color: #666;
    margin-bottom: 40px;
}

.terms-content {
    max-width: 900px;
    margin: 0 auto;
    background: white;
    border-radius: 10px;
    padding: 40px;
}

.terms-content h2 {
    font-size: 22px;
    color: #4a90e2;
    margin-top: 30px;
    margin-bottom: 15px;
}

.terms-content p {
    line-height: 1.8;
    margin-bottom: 15px;
    color: #666;
}

/* Responsive Design */
@media (max-width: 768px) {
    .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;
    }

    .course-grid-home {
        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;
    }
}