how change the space around two columns

Hello,

I’ve read a lot of the tutorial and some if it’s making sense now and I’m using the Vantage theme. I tried to recreate the nesting part on building a page and I can’t get one bit to work. I can’t get the space to the left and right of the green columns to change. I tried setting the padding left and right to 0 and the margin left an right to 0, in the widget css. I doesn’t seem to make any difference. Sorry for such a newbie question. Any help would be much appreciated.

http://thegreatchicken.net/