.book-container {
    display: none;
}

.book-container.active {
    display: flex;
}

.lessons-grid {
    margin: 15px;
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 10px;
}

.lesson-item {
    display: block;
    padding: 10px;
    background: #222222;
    border: none;
    border-radius: 10px;
    text-decoration: none;
    color: #aaaaaa;
    transition: all 0.3s ease;
    position: relative;
    overflow: hidden;
}

.lesson-item:hover {
    transform: translateX(8px);
    background: linear-gradient(135deg, #667eea, #764ba2);
    color: white;
    box-shadow: 0 10px 25px rgba(102, 126, 234, 0.3);
}

.lesson-item::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 4px;
    height: 100%;
    background: linear-gradient(135deg, #667eea, #764ba2);
    transform: scaleY(0);
    transition: transform 0.3s ease;
}

.lesson-item:hover::before {
    transform: scaleY(1);
}

.lesson-number {
    font-weight: 700;
    margin-left: 10px;
}

.lesson-title {
    font-weight: 500;
}

@media (max-width: 768px) {
    .lessons-grid {
        grid-template-columns: 1fr;
    }

}