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

.course-header {
    margin-bottom: 30px;
}

.course-header h1 {
    font-size: 28px;
    color: #333;
    margin-bottom: 10px;
}

.video-section {
    margin-bottom: 30px;
}

.video-player {
    width: 100%;
    background: #1a1a1a;
    border-radius: 12px;
    overflow: hidden;
    position: relative;
    aspect-ratio: 16/9;
}

.video-placeholder-course {
    width: 100%;
    height: 100%;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    display: flex;
    align-items: center;
    justify-content: center;
    position: relative;
    cursor: pointer;
}

.video-placeholder-course::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: url('data:image/svg+xml,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100"><circle cx="50" cy="50" r="40" fill="none" stroke="rgba(255,255,255,0.3)" stroke-width="2"/><circle cx="50" cy="50" r="30" fill="none" stroke="rgba(255,255,255,0.2)" stroke-width="1"/></svg>');
    opacity: 0.3;
}

.video-placeholder-course .video-play-btn {
    width: 80px;
    height: 80px;
    background: rgba(255, 255, 255, 0.95);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 1;
    transition: transform 0.2s;
    box-shadow: 0 4px 20px rgba(0,0,0,0.3);
}

.video-placeholder-course:hover .video-play-btn {
    transform: scale(1.1);
}

.video-placeholder-course .video-title {
    position: absolute;
    bottom: 30px;
    left: 50%;
    transform: translateX(-50%);
    color: rgba(255, 255, 255, 0.9);
    font-size: 18px;
    z-index: 1;
    background: rgba(0,0,0,0.5);
    padding: 10px 20px;
    border-radius: 20px;
}

.lesson-description {
    background: white;
    padding: 25px;
    border-radius: 12px;
    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
    margin-bottom: 30px;
}

.lesson-description h2 {
    font-size: 24px;
    color: #333;
    margin-bottom: 15px;
    padding-bottom: 10px;
    border-bottom: 2px solid #4a90e2;
}

.lesson-description p {
    font-size: 16px;
    line-height: 1.8;
    color: #666;
}

.lessons-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 20px;
    margin-top: 30px;
}

.lesson-card {
    background: white;
    border-radius: 12px;
    padding: 20px;
    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
    cursor: pointer;
    transition: transform 0.2s, box-shadow 0.2s;
    border-left: 4px solid #4a90e2;
}

.lesson-card:hover:not(.locked) {
    transform: translateY(-4px);
    box-shadow: 0 4px 16px rgba(0,0,0,0.15);
}

.lesson-card.active {
    background: #e3f2fd;
    border-left-color: #1976d2;
}

.lesson-card.locked {
    opacity: 0.6;
    cursor: not-allowed;
    border-left-color: #999;
}

.lesson-card.locked::after {
    content: '🔒';
    float: right;
    font-size: 20px;
}

.lesson-number {
    font-size: 14px;
    color: #666;
    margin-bottom: 8px;
}

.lesson-title {
    font-size: 18px;
    font-weight: 600;
    margin-bottom: 10px;
    color: #333;
}

.lesson-status {
    display: inline-block;
    padding: 4px 12px;
    border-radius: 12px;
    font-size: 12px;
    font-weight: 500;
}

.lesson-status.free {
    background: #e8f5e9;
    color: #2e7d32;
}

.lesson-status.locked {
    background: #f5f5f5;
    color: #757575;
}

@media (max-width: 768px) {
    .course-header h1 {
        font-size: 24px;
    }
    
    .lessons-grid {
        grid-template-columns: 1fr;
    }
    
    .lesson-description {
        padding: 20px;
    }
}