Try a view source on your page. You will see
<div class="centerColumn" id="productGeneral">
above the product info section. That class or ID would be a place to hang styling in your stylesheet.

I suggest you get the Firefox browser and its Web Developer extension. That will allow you to see and manipulate many aspects of your site. Try the Outline > Outline current element button, or Information > Display element information. CSS > Edit CSS will allow you to see effects of stylesheet edits instantly.