change multi category select appearance

[soura123]

hello is there any easy way ... from when i adding a product instead of the select box of multiple categories that it is now to become as the old virtuemart... on scroll box and to select multiple categories with ctrl???
i see with firebug on the category box the has that option but it is display : none that box... i try to find the specific css to change it to display block but i can not fount it any where ... any one to now please???

[soura123]

anyone???