[Forum] Forumblock with css for different styles

[(--eRRoR--)]

Hi there.I use vbulletin suite 4.1.4.I had untill now a dark bassed theme but now i installed a light bassed one to.I just modified the username colors to have invidual css definitions for each theme.Now i want to make the same thhing for my forum blocks.
For example i want to modify my facebook like box.
This is the code.

<div id="fb-root"></div><script src="http://connect.facebook.net/en_US/all.js#xfbml=1"></script><fb:like-box href="www.facebook.com/pages/Elite-Gamers/217730438249452" width="190" colorscheme="dark" show_faces="true" border_color="grey" stream="false" header="true"></fb:like-box>

how do i modifiy colorscheme="dark" to be taken from the additional.css because on the other theme i want to use colorscheme="white"

Thanks in advance.