#top_nav{
  display:none;
}

body { 
  background-color: #efefef;
  background-image:url("https://images.cnblogs.com/cnblogs_com/blogs/775556/galleries/2454607/o_250417131237_background.jpg"); 
  background-repeat: no-repeat; 
  background-attachment: fixed; 
  background-position: center 0; 
  background-size: cover; 
  padding-top:0px;
}