How do I seperate text styles...?

Basically the text that the AJAX Preview Popup Windows uses to display a preview of Product details uses the same style (size, font, color) as the style I use on the web page as the default font.  The problem is the main web page uses a black background, while the pop-up uses a white background, so needless to say I need to find a way to assign different, seperate styles to the ajax pop-up and the web page.  How do I achieve this?

 

Thanks

-Joe