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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'PingFang SC', 'Microsoft YaHei', sans-serif;
    background: #f8f9fa;
    min-height: 100vh;
    padding: 0;
}

.container {
    max-width: 1400px;
    margin: 0 auto;
    padding: 20px 20px;
}

header {
    text-align: center;
    margin-bottom: 30px;
    padding: 20px 20px;
    background: linear-gradient(135deg, #EF7F0F 0%, #ff9a56 100%);
    border-radius: 12px;
    color: white;
    box-shadow: 0 6px 20px rgba(239, 127, 15, 0.2);
}

.logo-container {
    margin-bottom: 8px;
}

.logo {
    max-width: 60px;
    max-height: 60px;
    object-fit: contain;
    filter: drop-shadow(0 2px 6px rgba(0, 0, 0, 0.15));
    transition: transform 0.3s ease;
}

.logo:hover {
    transform: scale(1.05) rotate(5deg);
}

header h1 {
    font-size: 1.6em;
    margin-bottom: 6px;
    font-weight: 700;
    letter-spacing: 0.5px;
}

.subtitle {
    font-size: 0.9em;
    opacity: 0.95;
    font-weight: 400;
}

/* 筛选按钮 */
.filter-section {
    display: flex;
    justify-content: center;
    gap: 12px;
    margin-bottom: 40px;
    flex-wrap: wrap;
    padding: 20px;
    background: white;
    border-radius: 16px;
    box-shadow: 0 2px 12px rgba(0, 0, 0, 0.06);
}

.filter-btn {
    padding: 12px 28px;
    border: 2px solid #e9ecef;
    border-radius: 12px;
    background: white;
    color: #495057;
    font-size: 15px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    overflow: hidden;
}

.filter-btn::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 0;
    height: 0;
    border-radius: 50%;
    background: rgba(239, 127, 15, 0.1);
    transform: translate(-50%, -50%);
    transition: width 0.6s, height 0.6s;
}

.filter-btn:hover::before {
    width: 300px;
    height: 300px;
}

.filter-btn:hover {
    border-color: #EF7F0F;
    color: #EF7F0F;
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(239, 127, 15, 0.15);
}

.filter-btn.active {
    background: #EF7F0F;
    color: white;
    border-color: #EF7F0F;
    box-shadow: 0 4px 16px rgba(239, 127, 15, 0.3);
}

/* 课程网格 */
.course-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
    gap: 30px;
    padding: 10px 0;
}

/* 课程卡片 */
.course-card {
    background: white;
    border-radius: 12px;
    overflow: hidden;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.06);
    transition: all 0.3s ease;
    cursor: pointer;
    border: 1px solid #e9ecef;
}

.course-card:hover {
    transform: translateY(-4px);
    box-shadow: 0 8px 20px rgba(239, 127, 15, 0.15);
    border-color: rgba(239, 127, 15, 0.3);
}

.course-content {
    padding: 20px;
    display: flex;
    flex-direction: column;
    gap: 10px;
}

.course-title {
    font-size: 17px;
    font-weight: 600;
    color: #212529;
    line-height: 1.5;
    transition: color 0.3s ease;
}

.course-card:hover .course-title {
    color: #EF7F0F;
}

.course-description {
    font-size: 14px;
    color: #6c757d;
    line-height: 1.6;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
    flex: 1;
}

.course-action {
    display: flex;
    align-items: center;
    justify-content: flex-end;
    gap: 8px;
    color: #EF7F0F;
    font-size: 14px;
    font-weight: 600;
    padding-top: 12px;
    border-top: 1px solid #f1f3f5;
    transition: all 0.3s ease;
}

.action-text {
    transition: transform 0.3s ease;
}

.action-arrow {
    width: 18px;
    height: 18px;
    transition: transform 0.3s ease;
}

.course-card:hover .action-text {
    transform: translateX(4px);
}

.course-card:hover .action-arrow {
    transform: translateX(6px);
}

@keyframes fadeIn {
    from {
        opacity: 0;
    }
    to {
        opacity: 1;
    }
}

@keyframes slideUp {
    from {
        transform: translateY(30px);
        opacity: 0;
    }
    to {
        transform: translateY(0);
        opacity: 1;
    }
}

/* 响应式设计 */
@media (max-width: 768px) {
    .container {
        padding: 20px 15px;
    }

    header {
        padding: 40px 20px;
        margin-bottom: 30px;
    }

    header h1 {
        font-size: 2em;
    }

    .subtitle {
        font-size: 1em;
    }

    .filter-section {
        padding: 15px;
        gap: 8px;
    }

    .filter-btn {
        padding: 10px 20px;
        font-size: 14px;
    }

    .course-grid {
        grid-template-columns: 1fr;
        gap: 20px;
    }

    .modal-content {
        max-height: 95vh;
        border-radius: 16px;
    }

    .modal-body {
        padding: 24px;
    }

    .modal-title {
        font-size: 22px;
    }

    .modal-meta {
        gap: 12px;
    }

    .meta-item {
        font-size: 13px;
        padding: 6px 12px;
    }

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

    .modal-footer {
        flex-direction: column;
        gap: 16px;
    }

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

    .enroll-btn {
        width: 100%;
    }
}