switch($_GET['css'])
{
        default:
        case 'style1':
         $css = '/styles/default.css';
         setcookie("css", $css, time()+3600*96);
        break;
        case 'style2':
         $css = '/styles/second.css';
         setcookie("css", $css, time()+3600*96);
        break;
}
$cssD = '/styles/default.css';
if (isset($_COOKIE["css"])) {
    $style = $_COOKIE['css'];
} else {
        $style = $cssD;
}