Wider Blog Post Setting

I love Ghost! I mean, I LOVE GHOST!!! It has solved every single problem that I had with other places. I only have one small issue that I would love to be able to fix. The blog posts themselves are somewhere around 800px wide from what I can tell. I would love to be able to extend this to 1100 or 1200 as that is my preferred width. Obviously, I am referring to desktop viewing. I downloaded the Casper theme and looked through the CSS and could not find a place where the width setting was for blog posts. Can anyone provide some insight?