body { 
     background-color: #efefef;
     background-image:url(https://images.cnblogs.com/cnblogs_com/crraphael/1518266/o_9cce5ebf959c405aa61db1a4f420550b.jpg); 
     background-repeat: no-repeat; 
     background-attachment: fixed; 
     background-position: center 0; 
     background-size: cover; 
    padding-top:0px;
  }

#clockdiv {
    /* left, center, right */
    text-align: center;
}