html, body {
    margin: 0;
    padding: 0;
    height: 100%;
    width: 100%;
  }
  
  body {
    background-image: url("desktop/desktop.png");
    background-size: cover;      
    background-position: center; 
    background-repeat: no-repeat; 
  }

  @media screen and (max-width: 768px) {
    body {
      background-image: url("phone/phone.png"); 
      background-size: cover;
      background-position: center;
      background-repeat: no-repeat;
    }
  }