how to remove border around twenty eleven navigation bar menu

First, create a child theme for your modifications so you don’t change the Twenty Eleven theme.

Then in the child theme’s style.css, add the following:

#access {
    box-shadow: none;
}

thanks but still didn’t do the trick?

Hmm, I’d have to see your site to tell you more. It worked on my copy. ??

I was looking for the same thing.
I tried pasting this into my child theme style.css and it worked.

#access  {
	-webkit-box-shadow: none;
	-moz-box-shadow: none;
	box-shadow: none;
}