index.html

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width,initial-scale=1.0,minimum-scale=1.0,maximum-scale=1.0,user-scalable=no">
  <title>Github Sample</title>
  <style type="text/css">
  	#test{
  		width: 200px;
  		height: 200px;
  		background-color: red;
  	}
  </style>
</head>
<body>
  <script type="text/javascript" src="sample.js"></script>
  <div id="test999">Hello World!</div>
</body>
</html>