CSS is not the easiest thing to get a handle on in short order.
dvdcollector.css contains the bulk of the page format while the second file contains the narrow left and bottom page panel areas.
I can point you in the direction of some good CSS resources if you like, or if you detail what it is you want to do and offer a page with content on it as a basis for comparison I'll be able to rework the code for you.
It's always difficult to look at an empty page and dream up changes based on your desire to "...stretch the information of each DVD across the page and maybe a little more colour..."
Actual content would go some way to helping solve the problem.