Best way to reverse engineer a template?

I’m a beginner – moderate html,php,css user. Basically I know a little about a lot, enough to do minor tweaks to a webpage at leaset. Right now I’m using dreamweaver and editing the css and php files directly. Changing a thing or 2 then refreshing the page but its a pretty slow process. I was wondering what would be the best way to do minor tweaks on a wordpress theme. I would need a program possible that would show me what and where in the css file I am while my mouse is pointing at it.. is there anything out there that does this?