.main-content.is-fullscreen:before {
  background-image:url(//s3.amazonaws.com/imagescloud/images/concours/sepaqmobile/20180501-m.jpg);
}

@media only screen and (min-width: 768px) {
  .main-content {
    background-image:url(//s3.amazonaws.com/imagescloud/images/concours/sepaqmobile/20180501.jpg);
  }
}