body:before {
    background: url(https://img2018.cnblogs.com/blog/1698312/201908/1698312-20190807094533352-141477054.png) center/cover no-repeat;
    content: '';
    background-repeat: no-repeat;
    background-position: center;
    opacity: 1;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: -1;
    -webkit-filter: grayscale(40%);
    -moz-filter: grayscale(40%);
    -ms-filter: grayscale(40%);
    -o-filter: grayscale(40%);
    filter: grayscale(40%);
    filter: gray;
}
#home{
opacity: 0.85;
}
body{
position: relative;
}
#zkh{
   position: absolute;
    z-index: 1;
    margin-top: 100px;
    margin-left: 260px;
}