body:before {
    background: url(https://img.alicdn.com/imgextra/i3/O1CN01aDYIho1DM6MYWMeVD_!!6000000000201-2-tps-2405-1089.png) center/cover no-repeat;
    content: '';
    background-repeat: no-repeat;
    background-position: center;
    /* opacity: 0.5; */
    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;
}