<!doctype html>
<html>
<head>
<style>
body {
      background-color: #808080;

      background-image:
      linear-gradient(45deg, #000000 25%, transparent 25%),
      linear-gradient(-45deg, #000000 25%, transparent 25%),
      linear-gradient(45deg, transparent 75%, #000000 75%),
      linear-gradient(-45deg, transparent 75%, #000000 75%);

      background-size:80px 80px;
      background-position: 0 0, 0 80px, 80px -80px, -80px 0px;
}
</style>
</head>
<body>
</body>
</html>