CONDENSE MARGINS WITH FULLWIDTH POST LAYOUT

Hello. When composing a new post with a fullwidth page layout, is there a way to shorten the left and right margins for the content, giving the appearance on a desktop of being centered on the page?

I’m basically trying to duplicate the margin size of the content area when a sidebar is included, only with eliminating that sidebar and pushing that content to the center of the screen.

Thanks for the help!

– jerhow