Using several CSS

Style sheets can be used to give a different presentation of your site, depending on the method used to view it. For example, it's possible to have a different presentation when you print a page to when you visualize it on your web browser. The control over the printing settings is by far the most interesting feature because it's even possible to manage page breaks in an html document.

To see the difference we use the media attribute, which gives us

<style type="text/css" media="screen"> ... </style>
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<link href="style.css" type="text/css" rel="stylesheet" media="print" >

screen denotes the viewing of the website in the browser and print refers to the printed document.

For more details, take a look at the standard: W3C