Adding A Background

Hello,

I am newish to wordpress and have moderate coding experience. I’d like to add a full-screen background to the site I am creating (www.dev.sbsa.info). I was able to do that- but it created unexpected results because the sidebars and content don’t start or end on the same line.

Is there a way to use the full-screen background and have the sidebars adjust to become the same size (I’d like it to look like a solid three-block wide unit) WITHOUT affecting the layout when the site is resized for a tablet or smart phone? (That is, I would like the sidebars to be the exact same height as the content only when viewed on a larger screen- once the site resizes for tablet/mobile, I’d like the sidebars to become only as long as they need to become to contain the widgets in each one).

Thanks!
John