This seems like a bug to me in virtuemart's search module:
I hacked it myself like this: (Joomla 2.5.4, Virtuemart 2.0.6)
Go to /modules/mod_virtuemart_search/mod_virtuemart_search.php
the 'hacked' beginning of the file should look like this:
<?php // no direct access
defined('_JEXEC') or die('Restricted access');
//Custom Hack(might get lost on next virtuemart-update!)
//appends virtuemart specific css to module, so this search module is stylable!
$document = JFactory::getDocument();
$document->addScriptDeclaration("
jQuery(document).ready(function($) {
$('div.search').parent().parent('.moduletable').attr('class', 'moduletablevmShopSearch');
})
");
?>
then u can add
div .moduletablevmShopSearch
{
}
to your template css.