body {
  margin: 0; 
  padding: 0;
  width: 100vw; 
  height: 100vh; 
  background-image: url("../img/bj.png"); 
  background-size: cover;
  background-position: center center; 
  background-repeat: no-repeat; 
  background-attachment: fixed; 
  background-color: #f0f0f0; 
}