You can find the entire stylesheet.css by going down further in the tree in the left pane and open up the Styles folder, and then open the *.css file there. Some books might name it something other than stylesheet.css, but the file will end in .css. Then you can compare each style to text within the book to see the differences.
Edit: Sorry this was for using Sigil, not Calibre, if that wasn't clear.
Last edited by Ripplinger; 05-19-2013 at 08:57 PM.