body {
	margin: 0;
	height: 100vh;
	background-image: linear-gradient(to bottom, rgba(0,0,0,0.5), rgba(0,0,0,0.5) 25%, rgba(255,255,255,0.5) 25%, rgba(255,255,255,0.5) 50%, rgba(0,0,0,0.5) 50%, rgba(0,0,0,0.5) 75%, rgba(255,255,255,0.5) 75%, rgba(255,255,255,0.5));
}

body::after {
	content: "";
  display: block;
	width: 100vw;
	height: 100vh;	
	background-image: linear-gradient(to right, rgba(0,0,0,0.5), rgba(0,0,0,0.5) 25%, rgba(255,255,255,0.5) 25%, rgba(255,255,255,0.5) 50%, rgba(0,0,0,0.5) 50%, rgba(0,0,0,0.5) 75%, rgba(255,255,255,0.5) 75%, rgba(255,255,255,0.5));
}