container and column width in twenty-ten

I’m using twenty ten and am trying to shrink the container down to 875px so it matches the other pages in the bigger site this blog is embedded in. I’m pretty sure my code is a mess at this point. I don’t really know what I’m doing and keep tweaking different lines with hope that something will budge… Can anyone help me? Fortunately, I’m working in a child theme so I can always start over if I have to, but I’d hate to lose the changes I’ve made that have worked… Any help or guidance is much appreciated. The site is here:
<www.benjaminnugent.com/news>

and the style.css is here:

[CSS moderated. All that is needed is a link to your site.]