I manage a couple of WordPress sites for my labgroup. Both of them use Twenty Eleven at this point. I’d like to decrease the margins, and have tried editing the CSS, and nothing I’ve tried has any effect at all on the appearance. I’ve got a premium plan, paid up. I’ve read all of the posts that the search function for the forum brought up for Twenty Eleven margins.
This is the front page of one of the sites: Front page. One of the weird things is that one of the pages actually has a much wider margin :Wider margin page and, while it’s a couple of years since I created that page, I don’t think I did anything different to it.