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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
}

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

header {
    background: white;
    border-radius: 10px;
    padding: 20px;
    margin-bottom: 30px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
}

h1 {
    color: #333;
    margin: 0;
}

h2 {
    color: white;
    margin-bottom: 20px;
}

.session-info {
    display: flex;
    gap: 15px;
    align-items: center;
}

.timer {
    background: #4CAF50;
    color: white;
    padding: 10px 20px;
    border-radius: 5px;
    font-weight: bold;
}

.expired {
    background: #f44336;
    color: white;
    padding: 10px 20px;
    border-radius: 5px;
}

.start-btn, .watch-btn {
    background: #2196F3;
    color: white;
    border: none;
    padding: 10px 20px;
    border-radius: 5px;
    cursor: pointer;
    font-size: 16px;
    text-decoration: none;
    display: inline-block;
}

.start-btn:hover, .watch-btn:hover {
    background: #1976D2;
    transform: translateY(-2px);
}

.video-grid {
    background: rgba(255,255,255,0.1);
    border-radius: 10px;
    padding: 20px;
}

.videos {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 20px;
}

.video-card {
    background: white;
    border-radius: 10px;
    overflow: hidden;
    transition: transform 0.3s, box-shadow 0.3s;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}

.video-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 5px 20px rgba(0,0,0,0.2);
}

.video-thumbnail {
    background: #f0f0f0;
    height: 200px;
    display: flex;
    align-items: center;
    justify-content: center;
}

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

.placeholder-thumbnail {
    font-size: 50px;
}

.video-info {
    padding: 15px;
}

.video-info h3 {
    margin-bottom: 10px;
    color: #333;
}

.video-info p {
    color: #666;
    font-size: 14px;
    margin-bottom: 10px;
}

.video-info small {
    color: #999;
    display: block;
    margin-bottom: 10px;
}

.watch-video-btn {
    display: inline-block;
    background: #4CAF50;
    color: white;
    padding: 8px 15px;
    text-decoration: none;
    border-radius: 5px;
    margin-top: 10px;
    transition: background 0.3s;
}

.watch-video-btn:hover {
    background: #45a049;
}

.watch-video-btn.disabled {
    background: #ccc;
    cursor: not-allowed;
}

@media (max-width: 768px) {
    header {
        flex-direction: column;
        text-align: center;
        gap: 15px;
    }
    
    .session-info {
        flex-direction: column;
    }
    
    .videos {
        grid-template-columns: 1fr;
    }
}