you must use a separate css file to print the page or use css3 media queries:
<link rel="stylesheet" href="css/print.css" type="text/css" media="print"/>
using percentage values, this is the best option when creating a css print file.
body, html, #wrapper { width: 100%; }
or in your main css file:
@media print { body, html, #wrapper { width: 100%; } }
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