body:before {
    background: url(https://images.cnblogs.com/cnblogs_com/2002ljy/1781104/o_210215121944d009b3de9c82d1582442d267820a19d8bd3e4220.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;
}
 #main,
  #topics,
  #mainContent,
  .postBody {
    overflow: visible;
  }
  #mainContent .forFlow {
    overflow: visible;
  }
  .zoom-overlay {
    background: transparent;
  }