/* 课程内容样式 */
.book-header {
    background: linear-gradient(rgba(0,0,0,0.5), rgba(0,0,0,0.5)), url('../../img/水浒传1.0.png');
    background-size: cover;
    background-position: center;
    color: white;
    text-align: center;
    padding: 60px 0;
    margin-bottom: 40px;
}