Removing header search bar only on mobile (twentyeleven child theme)

The blog is at http://www.directoroffootball.com.

On mobile and when the browser is really narrow, the search bar overlaps the title as you can see here, so I’d like to remove the search bar entirely once once the screen/browser is below a certain width. I’m not very hot on responsive design!

I’m using a child theme of twentyeleven.