body { 
     background-color: #efefef;
     background-image: url(https://img2018.cnblogs.com/blog/1584426/201903/1584426-20190323113911768-31486007.jpg);
     background-repeat: no-repeat; 
     background-attachment:fixed; 
     background-position: center 0; 
     background-size: cover; 
  }