HTML Image full screen width

HTML

<!DOCTYPE html>
<html>
<head>	
  
	<style>
		body{ margin:0px }
		div#middle > div{ float:left; width:100%; }
		div#middle > div > div > img{ width:100%; }
	</style>
</head>

<body>
  <div id="middle">
		<div>
			<div>
				<img src="example.jpg" alt="example">
			</div>
		</div>
	</div>
 </body>
</html>

Source