Decreasing Margin/Padding

I currently have the Mystile theme installed on: http://beautenature.biz.

I would like to decrease the white margin/padding from the sides and let the green background image come up right to the page content.

I’ve looked through the CSS style and can’t seem to find the right section to edit. The stylesheet is located here: http://beautenature.biz/wp-content/themes/mystile/style.css

Help would be appreciated, thanks!