body {
  background-image: url(images/background-photo.png);
  background-position: center center;
  background-repeat: no-repeat;
  background-attachment: fixed;
  background-size: 70%;
  background-color:#FFF;
}

@media only screen and (max-width: 767px) {
  body {
    background-image: url(images/background-photo-mobile-devices.png);
    background-size: 120%;
  }
}