if you want to have a different style based on a query string.
EG:
www.mysite.com?style=1
you can do it like this
Code:
<?php
switch($_GET['style']) {
case 1:
$style="style.css";
break;
case 2:
$style="style2.css";
default:
$style="style.css";
break;
}
?>
then in <head>
Code:
<link rel="stylesheet" href="<?php echo $style; ?>" type="text/css">