<html>
<head>
<title>CSS3 media query test: relative constraints test using screen and (min-width: 30em). Using style element, css @media rule </title>  
<link rel="help" href="http://www.w3.org/TR/css3-mediaqueries/#width" />

<style type="text/css">
p {
  color: red;
}
@media screen and (min-width: 30em) {
   p {
     color: green;
  }
}
</style>
</head>
<body>

<p> This text should be green if viewport is wider than 30em.  </p>

<div style="width: 30em; background-color: lightblue;"> div of length 30 em </div>
<div style="width: 800px; background-color: lightblue;"> div of length 800px </div>
</body>
</html>