body:before {
    background: url(https://img2020.cnblogs.com/blog/1663226/202003/1663226-20200304121147931-844039512.jpg) center/cover no-repeat;
    content: '';
    background-repeat: no-repeat;
    background-position: center;
    opacity: 0.8;
    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: 0.9;
margin: 0 auto;
width: 85%;
min-width: 950px;
background-color: #fff;
padding: 30px;
margin-top: 30px;
margin-bottom: 50px;
box-shadow: 0 2px 6px rgba(100, 100, 100, 0.3);
}