colored background on half the page – using CSS

I am getting my feet wet with CSS.

I would like the top half of my page with a white background (like all my other pages)

But the bottom half of the page to have a background color.

I tried adding a class (division) : .memarea to my CSS

But it seems this area is not considered part of my regular post. What am I doing wrong?

Page:

http://choveveitzion.com/plumbing/

Thank you!!!