I'm learning CSS and creating a blog at annieagarwal.com/blog (again, work in progress!)

I want to recreate the shadow on the sides of the main container of this blog http://www.robincornett.com/

How do I do that?
The blog has two style sheets
http://www.robincornett.com/wp-conte...oto2/style.css
http://www.robincornett.com/wp-conte...stom.css?55140

My style sheet is at
http://annieagarwal.com/blog/wp-cont...ious/style.css

I created a png of the shadow that is 1000px wide at http://annieagarwal.com/blog/wp-cont...ges/shadow.png

But I can't seem to get the code right. I want to use a background image/color along with the container having a drop shadow.