*{
    margin: 0;
    padding: 0;
    list-style: none;
}
.header{
height: 100vh;
}
.video-background{
    position: absolute;
    right:0;
    bottom: 0;
    min-width: 100%;
    min-height: 100%;
    width: auto;
    height: auto;
    z-index:-1;
}
@media(min-aspect-radio:16/9){
    .video-background{
        width: 100%;
        height: auto;
    }
}
@media(max-aspect-radio:16/9){
    .video-background{
        width: auto;
        height: 100%;
    }
}
.nav_bg{
    width: 100%;
    height: 60px;
    background: transparent;
}
.nav_bg .nav{
    width: 1000px;
    height: 60px;
    margin: 0 auto;
}
/*一级菜单*/
.nav_bg .nav .list_one .mean_one{/*一级导航*/
    float:left;
    width: 200px;
    height: 60px;
    line-height: 60px;
    text-align: center;
    position: relative;   /*固定区块*/
    background:rgba(255, 255, 255, .1);
    border-radius: 4px;   /*按钮弧度*/
}
a:link {text-decoration:none;color: #ffffff;}/*删除下划线*/
a:visited {color:#ffffff;}

.nav_bg .nav .list_one .mean_one .list_two{/*二级导航*/
    display: none;
    width: 100%;
    position: absolute;
    top: -200px;
    left: 0;
    background:rgba(0, 0, 0, .1); /*背景颜色*/
}
/*鼠标经过时二次菜单出现*/
.nav_bg .nav .list_one .mean_one:hover .list_two{
    display: block;
    top:60px;

}
.nav_bg .nav .list_one .mean_one a:hover{
    background: rgba(0, 0, 0, .1);
}
.nav_bg .nav .list_one .mean_one a:hover{
    width: 100%;
    height: 60px;
    display: block;
}
.botton-text{
    width: auto;
    height:500px;
    position: fixed
    bottom:0;    
}