It works when use "body:before"

body:before {
  content: ' ';
  position: fixed;
  z-index: -1;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  background-repeat: no-repeat;
  background-size: cover;
  background-color: transparent;
  background:url(/images/background.jpg);
  background-position:50% 50%;
}