body {
  background: none;
  background-image: url("files/background/test-4.jpeg");
  background-position: center top;
  background-repeat: no-repeat;
  background-attachment: fixed;
  background-size: auto;
}
body.isMobile .body-background {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100vh;
  z-index: -10;
  background-image: url("files/background/test-4.jpeg");
  background-position: center top;
  background-repeat: no-repeat;
  background-size: auto;
}