#header{display:none;} /* 将默认的导航头屏蔽掉 */
/* 背景图片 */
body { 
     background-color: #efefef;
     background-image:url(https://i.loli.net/2020/11/01/eNX6AusmwLb5Vcn.jpg); 
     background-repeat: no-repeat; 
     background-attachment: fixed; 
     background-position: center 0; 
     background-size: cover; 
     padding-top:0px;
     opacity:0.8
  }