.books-nav {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(400px, 1fr));
    grid-auto-rows: 1fr;
    gap: 100px;
    padding: 100px;
    box-shadow: 0 20px 40px rgba(0, 0, 0, 0.1);
}

.book-card {
    border-radius: 16px;
    background-color: #ffffff;
    color: #2d3748;
    text-align: center;
    box-shadow: 0 8px 24px rgba(59, 130, 246, 0.05);
    cursor: pointer;
    transition: all 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
    position: relative;
    overflow: hidden;
    display: flex;
    justify-content: center;
    align-items: center;
    border: 1px solid #e2e8f0;
}

.book-card img {
    border-radius: 12px;
    width: 50%;
    height: 50%;
    object-fit: cover;
}

.book-card .book-info {
    flex: 1;
    padding: 0 10px;
}

.book-card:hover {
    transform: translateY(-10px) scale(1.02);
    box-shadow: 0 16px 32px rgba(59, 130, 246, 0.2);
    background: linear-gradient(135deg, #3b82f6, #60a5fa);
    color: white;
}

.book-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.6), transparent);
    transition: left 0.5s;
}

.book-card:hover::before {
    left: 100%;
}


.book-number {
    margin-top: 10px;
    font-size: 20px;
    font-weight: bold;
    margin-bottom: 10px;
    color: #3b82f6;
    flex: 1;
}

.book-card:hover .book-number {
    color: white;
}

.book-title {
    font-size: 15px;
    font-weight: bold;
    margin-bottom: 10px;
    color: #2d3748;
}

.book-subtitle {
    font-size: 12px;
    margin-bottom: 10px;
    color: #718096;
}

.lesson-count {
    background: rgba(59, 130, 246, 0.1);
    padding: 8px 16px;
    border-radius: 25px;
    font-size: 10px;
    margin-bottom: 10px;
    color: #3b82f6;
}

.book-card:hover .lesson-count {
    background: rgba(255, 255, 255, 0.2);
    color: white;
}

@media (max-width: 768px) {
    .books-nav {
        grid-template-columns: 1fr;
        gap: 40px;
        padding: 40px;
    }

}

/* 学习路径建议样式 */
.learning-path {
    background-color: #f8fafc;
    border-radius: 16px;
    padding: 40px;
    margin: 40px auto;
    max-width: 1200px;
    border: 1px solid #e2e8f0;
    box-shadow: 0 8px 24px rgba(59, 130, 246, 0.05);
    animation: fadeInUp 1s ease-out 0.3s both;
}