@media only screen and (min-width : 1025px) {
  html {
    background: url(bg-desktop.jpg) no-repeat center center fixed;
    background-size: cover;
    height: 100%;
    overflow: hidden;
  }
}

@media only screen and (max-width : 415px) {
  html {
    background: url(bg-mobile.jpg) no-repeat center center fixed;
    background-size: cover;
    height: 100%;
    overflow: hidden;
  }
}

@media only screen and (min-width : 200px) and (max-width : 767px) and (orientation : landscape) {
  html {
    background: url(bg-desktop.jpg) no-repeat center center fixed;
    background-size: cover;
    height: 100%;
    overflow: hidden;
  }
}
@media only screen and (min-device-width : 768px) and (max-device-width : 1024px) and (orientation : portrait) {
  html {
    background: url(bg-tablet-portrait.jpg) no-repeat center center fixed;
    background-size: cover;
    height: 100%;
    overflow: hidden;
  }
}
@media only screen and (min-device-width : 768px) and (max-device-width : 1024px) and (orientation: landscape) {
  html {
    background: url(bg-mobile-landscape.jpg) no-repeat center center fixed;
    background-size: cover;
    height: 100%;
    overflow: hidden;
  }
}