Dreamwidth style system discussion

I've been trying to fix my comment-width - one of the major problems I find with the custom comment pages is the comments squidge up really really quickly - but even setting width with ems doesn't help if you're on a browser with a different window size.

So, mainly: is there a way where I can set comment width = post width?

I'd prefer to keep it that simple - having auto-resizing layouts is also good - but if it's impossible that's good to know, too.