Very Basic Help Needed

I'm not sure where to post this (cannot access hackyourlefora for some odd reason) but here it goes: How can I change the background color and font type/size of the following titles, see attached:

I've tried a few things with my css but they do not seem to work...I want to change the font size in the header bar (Forum, Headlines, Members, About) to smaller and bold the category group titles and increase the spaces between letters and change also the background color..oh, and also remove the dotted line below these.

Thanks for your help once again!