Doesn't work at all

Hey all,

I’m trying to change the menu’s colour. I first followed this thread : http://wordpress.org/support/topic/twenty-eleven-menu-bar-color but none of the recommendations (modify the css and add your plugin) worked.
Here’s my website : lechoresponsable.org
Would someone be able to help me diagnosing the problem?

Regards, Baptiste.

http://wordpress.org/extend/plugins/styles/