article {
	background-color: #EEE;
	}
h1 {
	color: #AAC;
	font-size: 4.5vh;
	text-shadow: 0px 0px 0.6em #447, 0.02em 0.02em 0.15em #000;
	}

#patcont {
	position: absolute;
	top: 50%;
	left: 50%;
	transform: translate(-50%, -50%);
	display: block;
	width: 600px;
	height: 600px;
	background-color: #FFF;
	}
#pata, #patb {
	position: absolute;
	width: 600px;
	height: 600px;
	background-image: url("math-images/checkerboard-20-100.gif");
	background-repeat: repeat;
	}