.book-container {
    display: none;
}

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

.book-container.active::after {
    content: "\0040\0068\006F\006F\0074\0068\0069\006E";
    position: absolute;
    right: 18px;
    bottom: 18px;
    font-size: 12px;
    color: rgba(255, 255, 255, 0.02);
    letter-spacing: 0.4px;
    pointer-events: none;
    user-select: none;
}

/* Navigation buttons in book-header */
.book-header .nav-btn {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 44px;
    height: 44px;
    padding: 0;
    background: var(--container-highlight);
    color: var(--text-color);
    border: 1px solid transparent;
    border-radius: 50%;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    flex-shrink: 0;
}

.book-header .nav-btn svg {
    width: 20px;
    height: 20px;
    transition: transform 0.3s ease;
}

.book-header .nav-btn:hover:not(:disabled) {
    background: var(--primary-color);
    border-color: var(--primary-color);
    transform: scale(1.1);
    box-shadow: 0 4px 15px rgba(29, 185, 84, 0.4);
}

.book-header #prev-book:hover:not(:disabled) svg {
    transform: translateX(-2px);
}

.book-header #next-book:hover:not(:disabled) svg {
    transform: translateX(2px);
}

.book-header .nav-btn:active:not(:disabled) {
    transform: scale(1.0);
}

.book-header .nav-btn:disabled {
    opacity: 0.2;
    cursor: not-allowed;
}

@media (max-width: 768px) {
    .book-header {
        gap: 12px;
    }

    .book-header .nav-btn {
        width: 36px;
        height: 36px;
    }

    .book-header .nav-btn svg {
        width: 18px;
        height: 18px;
    }

    .book-header img {
        max-width: 60px;
    }
}

.lessons-grid {
    margin: 15px 0;
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 15px;
}

.lesson-item {
    display: block;
    padding: 15px 20px;
    background: var(--container-highlight);
    border-radius: 8px;
    text-decoration: none;
    color: var(--text-color-dark);
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    border: 1px solid transparent;
    position: relative;
    overflow: hidden;
}

.lesson-item::before {
    content: '';
    position: absolute;
    left: 0;
    bottom: 0;
    width: 0;
    height: 3px;
    background: linear-gradient(90deg, var(--primary-color), #1ed760);
    transition: width 0.4s cubic-bezier(0.4, 0, 0.2, 1);
}

.lesson-item:hover::before {
    width: 100%;
}

.lesson-item:hover {
    transform: translateY(-4px) scale(1.01);
    background: linear-gradient(135deg, #333 0%, #3a3a3a 100%);
    color: var(--text-color);
    border-color: var(--primary-color);
    box-shadow: 0 8px 20px rgba(29, 185, 84, 0.15),
                0 4px 10px rgba(0, 0, 0, 0.3);
}

.lesson-item:active {
    transform: translateY(-2px) scale(1.0);
}

.lesson-item.last-read {
    background: linear-gradient(135deg, rgba(29, 185, 84, 0.15) 0%, rgba(29, 185, 84, 0.05) 100%);
    border-color: var(--primary-color);
    box-shadow: 0 0 15px rgba(29, 185, 84, 0.3);
}

.lesson-item.last-read::before {
    width: 100%;
}

.lesson-item.last-read .lesson-number {
    color: var(--primary-color);
}

.lesson-number {
    font-weight: 700;
    color: var(--text-color);
    margin-right: 10px;
}

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

@media (max-width: 768px) {
    .lessons-grid {
        grid-template-columns: 1fr;
        gap: 10px;
    }

}