/* css/main.css */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.6;
    color: #333;
    background-color: #f8f9fa;
}

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

/* 头部导航 */
.header {
    background: white;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
    position: sticky;
    top: 0;
    z-index: 1000;
}

.navbar {
    padding: 1rem 0;
}

.nav-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo h1 {
    color: #3498db;
    font-size: 1.8rem;
}

.nav-menu {
    display: flex;
    list-style: none;
    gap: 2rem;
}

.nav-menu a {
    text-decoration: none;
    color: #333;
    font-weight: 500;
    transition: color 0.3s;
}

.nav-menu a:hover,
.nav-menu a.active {
    color: #3498db;
}

.search-box {
    display: flex;
    gap: 0.5rem;
}

.search-box input {
    padding: 0.5rem 1rem;
    border: 1px solid #ddd;
    border-radius: 4px;
    width: 250px;
}

.search-box button {
    padding: 0.5rem 1rem;
    background: #3498db;
    color: white;
    border: none;
    border-radius: 4px;
    cursor: pointer;
}

.auth-buttons {
    display: flex;
    gap: 1rem;
}

.btn-login,
.btn-register {
    padding: 0.5rem 1rem;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    font-weight: 500;
}

.btn-login {
    background: transparent;
    color: #3498db;
    border: 1px solid #3498db;
}

.btn-register {
    background: #3498db;
    color: white;
}

.btn-back {
    background: green;
    color: yellow;
}

/* 英雄横幅 */
.hero-banner {
    background: linear-gradient(135deg, #3498db, #2c3e50);
    color: white;
    padding: 4rem 0;
    text-align: center;
}

.banner-content h2 {
    font-size: 2.5rem;
    margin-bottom: 1rem;
}

.banner-content p {
    font-size: 1.2rem;
    margin-bottom: 2rem;
    opacity: 0.9;
}

.cta-button {
    padding: 0.8rem 2rem;
    background: #e74c3c;
    color: white;
    border: none;
    border-radius: 4px;
    font-size: 1.1rem;
    cursor: pointer;
    transition: background 0.3s;
}

.cta-button:hover {
    background: #c0392b;
}

/* 课程部分 */
.course-section {
    padding: 4rem 0;
}

.section-title {
    text-align: center;
    font-size: 2rem;
    margin-bottom: 2rem;
    color: #2c3e50;
}

.course-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 2rem;
}

.course-card {
    background: white;
    border-radius: 8px;
    overflow: hidden;
    box-shadow: 0 4px 6px rgba(0,0,0,0.1);
    transition: transform 0.3s, box-shadow 0.3s;
}

.course-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 15px rgba(0,0,0,0.1);
}

.course-thumbnail {
    height: 180px;
    background: #3498db;
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
    font-size: 1.5rem;
}

.course-info {
    padding: 1.5rem;
}

.course-title {
    font-size: 1.2rem;
    margin-bottom: 0.5rem;
    color: #2c3e50;
}

.course-meta {
    display: flex;
    justify-content: space-between;
    color: #7f8c8d;
    font-size: 0.9rem;
    margin-bottom: 1rem;
}

.course-description {
    color: #7f8c8d;
    font-size: 0.9rem;
    line-height: 1.5;
}

/* 页脚 */
.footer {
    background: #2c3e50;
    color: white;
    text-align: center;
    padding: 2rem 0;
    margin-top: 4rem;
}

/* 响应式设计 */
@media (max-width: 768px) {
    .nav-container {
        flex-direction: column;
        gap: 1rem;
    }

    .search-box input {
        width: 200px;
    }

    .banner-content h2 {
        font-size: 2rem;
    }

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