#main_container{
    display: flex;
    justify-content: center;
    width: 1000px;
    margin: 20px auto;

}
#left_div{
    position: relative;
    margin-right: 30px;
}
#content_div{
    padding-top: 20px;
    padding-left: 50px;
    border-left: 1px solid rgba(0, 0, 0, 0.2);
    width: 640px;
    height: 240px;

}
.left_item{
    width: 100px;
    height: 20px;
    line-height: 20px;
    padding: 10px 30px;
    margin: 20px 0px;
    text-align: center;
    cursor: pointer;
    position: relative;
    z-index: 9;
    color: rgba(0, 0, 0, 0.4);
}
#item_epub{
    font-style: italic;
}
#content_epub{
    display: block;
    line-height: 25px;
}
#content_pdf{
    display: none;
    line-height: 25px;
}
#content_browser{
    display: none;
    line-height: 25px;
}
#content_notice{
    white-space: pre-wrap;
    display: none;
    line-height: 25px;
}
#slider_hover{
    position: absolute;
    top: 20px;
    background-color: rgba(255, 165, 162, 0.51);
    width: 160px;
    height: 40px;
    border-radius: 8px;
    z-index: 5;
}