body { 
     background-color: #efefef;
     background-image: url(https://images.cnblogs.com/cnblogs_com/blogs/746940/galleries/2141368/o_220409120115_wallhaven-rdw8dj.jpg);
     background-repeat: no-repeat; 
     background-attachment: fixed; 
     background-position: center 0; 
     background-size: cover; 
     opacity: 0.8;
  }