#bg {
  position: fixed;
  top: 0%;
  left: 0%;
  width: 100%;
  height: 100%;
  z-index: -1;
}
#bg img {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  width: 100%;
  height: 100%;
  z-index: -1;
}