<!DOCTYPE html>
<html>
<head>
<style>
body {
	margin: 0;
	padding: 0;
}

.square {
	height: 256px;
	width: 256px;
}
</style>
</head>
<body>
<div class="square" style="background-color: red" id="red"></div>
<div class="square" style="background-color: green" id="green"></div>
</body>
</html>