#main {
    width: 1200px;
    margin: 375px 20%;
    clear: both;
z-index: 1;
}
body {
            background: url(https://images.cnblogs.com/cnblogs_com/leaf-cq/1810346/o_200721033841cc.jpg) repeat scroll 0 0 #f0eef5;
}
#header{
position: fixed;
left:20%;
top:0px;
z-index: 200;
}