#top_nav{display:none;}

#back-to-top {
    background-color: #7B7788;
    bottom: 0;
    box-shadow: 0 0 6px #7B7788;
    color: #444444;
    padding: 5px 5px;
    position: fixed;
    right: 50px;
    cursor: pointer;
}




#page_begin_html{
padding: 0
}

#leo{
margin: 0;
padding: 0;
}

.nav{
display: inline-block;
margin-right: -3px;
margin-left: 0px;
padding: 0px;
list-style-type: none; /*去除li前的标注*/
background-color: #3333;
overflow: hidden; /*隐藏溢出的部分，保持一行*/

}

.dropbtn {
display: inline-block; /*设置成块*/
color: white;
text-align: center;
text-decoration: none;
padding: 1px 1px;
}

.dropdown-content{
    display: none;
    position: absolute;
    background-color: #f9f9f9;
    min-width: 160px;
    box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
}
.nav:hover .dropdown-content{
     display: block;
     clear: both;
}