looking at your site…. none of the css has been changed – here is your code
#access {
background: #222; /* Show a solid color for older browsers */
background: -moz-linear-gradient(#252525, #0a0a0a);
background: -o-linear-gradient(#252525, #0a0a0a);
background: -webkit-gradient(linear, 0% 0%, 0% 100%, from(#252525), to(#0a0a0a)); /* older webkit syntax */
background: -webkit-linear-gradient(#252525, #0a0a0a);
be aware that all of those background lines would need some sort of change. the first one is the fallback for all browsers not supporting the gradient property. The next 4 lines are all proprietary broser specific gradients for the menu bar.
If you don’t wish to have the gradient, and just want your colour, delete the four lines, and just keep that top line with your colour
Also, I see you are editing 2011 directly, which is not good, as you will soon lose your changes
https://vudu.me/child
That explains child themes, the article is about the 2010 theme, but the basis is the same for all themes