body {
color: #000;
background: url(https://images.cnblogs.com/cnblogs_com/zhucheng88/1760433/o_200806014340background2.jpg) fixed;
background-size: 100%;
background-repeat: no-repeat;
opacity:0.95
}

#top{
background: url(https://images.cnblogs.com/cnblogs_com/zhucheng88/1760877/o_200509022843Banner1.jpg) fixed;
background-size: 100%;
background-repeat: no-repeat;
height:20%;
}

#back-top {
       position: fixed;
       bottom: 10px;
       right: 5px;
       z-index: 99;
  }
  #back-top span {
       width: 100px;
       height: 100px;
       display: block;
       background:url(https://images.cnblogs.com/cnblogs_com/zhucheng88/1819656/o_200804014434returnTop2.png) no-repeat center center;
       background-size: contain;
  }
  #back-top a{outline:none}