*{margin: 0px;padding: 0px;}

#book_nav{
    margin: 20px 0 0 40px;
}
#book_nav>ul> li{
    padding: 10px;
}
#book_nav li:hover{
    cursor: pointer;
}
#book_nav a{
    text-decoration: none;
}
#book_nav span:hover{
    background-color: skyblue;
}

#menu1_2,#menu2_2,#menu3_2{
    margin-top: 10px;
    display: none;
}
#menu1_2 a,#menu2_2 a,#menu3_2 a{
    margin-left: 20px;
    line-height: 25px;
}
#menu1_2 li,#menu2_2 li,#menu3_2 li{
    list-style-type: none;
}

.book-main{
    margin: 20px 0 0 20px;
}
.book-main>h3{padding: 5px;}
.book-main>p, .book-main>li{
    text-indent: 2em;
}

.top-img{
    margin: 50px auto;
}