Whiteboard – how to resize?

Hello,
I’m working with a responsive theme for the first time, and have a need to resize the default layout.

First of all, there are so many .css files in this theme that I really don’t know where to start.

Second, although I’ve read up on responsive themes, I still can’t figure out how to set the width of the content area/sidebar to my liking, especially the padding to the left and right of the content and sidebar, which seems entirely too thick.

The site I’m working on is here; http://crs-help.ca/blog/ and it needs to match the layout of http://crs-help.ca/index.html

Any leads would be very much appreciated!