@media screen and (min-width: 920px) {
  #header .hero{
    background-image: url('../../img/bg/index_hero_desktop.jpg');
  }

}
@media screen and (max-width: 919px) {
  #header .hero{
    background-image: url('../../img/bg/index_hero_tablet.jpg');
  }

}
@media screen and (max-width: 639px) {
  #header .hero{
    background-image: url('../../img/bg/index_hero_mobile.jpg');
  }

}