body {
  height: 100vh;
  background-image: url(../img/background.jpg);
  background-size: 110% 110%;
  background-position: center center;
  animation: shrink 8s infinite alternate;
}
@keyframes shrink {
  0% {
    background-size: 110% 110%;
	background-attachment: fixed;
  }
  100% {
    background-size: 120% 120%;
	background-attachment: fixed;
  }
}