body {
  background-image: url(/img/marientreppe.png);
  background-position: center center;
  background-repeat: no-repeat;
  background-attachment: fixed;
  background-size: cover;
  background-color:#464646;
 
  /* SHORTHAND CSS NOTATION
   * background: url(background-photo.jpg) center center cover no-repeat fixed;
   */
}

@media only screen and (max-width: 767px) {
  body {
    background-image: url(/img/marientreppe.png);
  }
}