The style.css file for Twenty Ten is a bit large.
If you are just trying to change the colors of the buttons, that might be “not too hard.” Other more significant changes could be daunting.
The way I made my changes was to use Firebug addon in Firefox to locate the selectors that mattered. Things like:
#access a
#access ul ul a
#access ul ul :hover > a
#access ul li.current-menu-parent > a
If the above stuff looks too unfamiliar or scary weird, you might want to reconsider messing with the css.
If the above stuff looks like you might recognize it, then just make sure to create a backup of the style.css file before messing around.
