body:before {
    background: url(https://img2022.cnblogs.com/blog/2486396/202207/2486396-20220711171312748-1928335490.jpg) center/cover no-repeat;
    content: '';
    background-repeat: no-repeat;
    background-position: center;
    opacity: 0.30;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 120%;
    z-index: -1;
    -webkit-filter: grayscale(10%);
    -moz-filter: grayscale(10%);
    -ms-filter: grayscale(10%);
    -o-filter: grayscale(10%);
    filter: grayscale(10%);
    filter: gray;
}