body:before {

background: url(https://img2018.cnblogs.com/blog/1646268/201906/1646268-20190625093618683-318547492.jpg) center/cover no-repeat;

content: ''; background-repeat: no-repeat;

background-position: center;

opacity: 0.08;

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;

}