Need FireBug & Customization help, please!

[gizmo_girl]

I am building a new website using version 1.5.1 (www dot personalizetpetid dot com)

First of all, I am using FireBug to play around with the stylesheet, etc, to find where to make changes for font colors, etc. The problem I have, is that I can find the line of code in the html/php files, but I cannot find WHICH file(s) to edit to make my changes permanent. The first image attached shows where I have a facebook button I want to edit. I found the line of code using FireBug...but how do I find which FILE it's in?

Second, I want to add a bar with a colored background along the top, where I've indicated in the second image. I assume that would be in the stylesheet (??) somewhere, but which one and what code would I use? There is an outline around the invisible box when I inspect it, but I can't figure out what to add to make it add a colored box in that place.

Any help is greatly appreciated!!