Adding a colored background under the text

Hi. I need a little help.
Well, i use the “Default” theme, based on kubrick.
The problem is following. I want to add a coloured background to my posts.
I want one colour for the heading, and one for the post.
The problem is, i won’t find the right place in the css to add this. I have been sitting here in 6 hours messing with this. The Div Class name is “post”, and i thought adding
background-color: #FCFCFC; to the Css under .post would solve the problem, but no.
Therefore, i need your help!