Here's a quick color guide showing what changes what which you can do by adjusting in EXTRA.CSS tempate though I'm sure it can all be done through style properties also.
It does... and at first it can get to be confusing. After you play with it a bit then you will start to grasp it. It took me a while - but look at me now, I can even give help to others at times!
Suggestion... make a child style of your current style and then go to town playing with it (tweaking here and there to see what changes). Do NOT make it a style that users can choose (you will still be able to since you are an Admin). If you have a developer board set up then you can just do it on that - but when I first started I hadn't set up a separate restricted site (I have one now on my server here at the house that I duplicate all my forums on but I still find that I do my tweaking on a child style of my live site).