.landing-page {
    left:0;
    width:100%;
    height:100%;
}

@media only screen and (max-width: 767px) {
    .landing-page {
      background: url(images/Landing_page_mobile.jpg) no-repeat top center;
      background-size: cover;
    }
}

@media only screen and (max-width: 991px) and (min-width: 768px) {
    .landing-page {
      background: url(images/Landing_page_tablet.jpg) no-repeat top center;
      background-size: cover;
    }
}

@media only screen and (min-width: 991px) and (max-width: 1024px) {
    .landing-page {
      background: url(images/Landing_page_tablet.jpg) no-repeat top center;
      background-size: cover;
    }
}