body {
  background-image: url('/images/accueil/fond-nature.jpg');
  background-repeat: no-repeat;
  background-position:center top;
  background-size:cover;
  background-attachment: fixed;
}


@media only screen and (max-width:640px) {
  body {
    background-image: url('/images/accueil/nature-mobile.jpg');
    background-repeat: no-repeat;
    background-position:center top;
    background-size:cover;
    background-attachment: fixed;
  }

}