Defining A CSS Selector That Requires A Multi-Class Union 

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
	<title>CSS Test</title>
 
	<style type="text/css">
 
		p {
			padding: 5px 5px 5px 5px ;
			}
 
		p.one {
			border: 1px solid black ;
			}
 
		p.two {
			background-color: gold ;
			}
 
		/* ---- Here's where is gets crazy ---- */
		p.one.two {
			color: white ;
			}
 
	</style>
</head>
<body>
 
	<p class="one">
		Only One
	</p>
 
	<p class="two">
		Only two
	</p>
 
	<p class="one two">
		Both One And Two
	</p>
 
</body>
</html>

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