Change full width display of the site into content in box/wrapper

Hi,

First of all, thanks again for the great theme!

To all the great souls who actively helping others solving problems on the forum, thank you all!.

I am helping a friend to set up the site and he’s more interested in the site display in a set wrapper/box instead of full width fluid effect across the browser. Please could anyone point out direction to me as to how to tweak the css code to achieve that, e.g., if I were to have a 980 width display and put content into a background which shows light grey drop shadow as the edge of the wrapper/box?

Many thanks!