<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Grid</title>
<style>
body {
background: #fff;
}
.r {background: red; width: 300px; height: 50px}
.g {background: green; width: 300px; height: 50px}
</style>
</head>
<body>
<div class=r></div>
<div class=g></div>
<div class=r></div>
<div class=g></div>
<div class=r></div>
<div class=g></div>
</body>
</html>