I recently created a theme (based on subSilver) for the first time, using CSS. It's a white-on-black color scheme (with some purple and blue-green here and there) and it turned out pretty well, except there is one place (that I can remember right now) that still has a white background, with white text on it, which is odd, to say the least. It's the font-size drop-down menu:

I can't find in the CSS where to change either the background or the text of this drop-down menu. Help is appreciated.
Thanks