body { 
     background-color: #efefef;
     background-image: url(https://uploadbeta.com/api/pictures/random/?key=%E6%8E%A8%E5%A5%B3%E9%83%8E);
     background-repeat: no-repeat; 
     background-attachment: fixed; 
     background-position: center 0; 
     background-size: cover; 
  }