Navigation bar not coded properly

Hi,

I am building a website using wordpress, and ofcourse I am using a child theme. Now, I was making some changes to my blog (Twenty Eleven Theme) but now I seem to have changed something to the navigation bar. The vertical height seems shorter and now I cannot reach my submenus since there is ‘space’ between them. Here is the link to my site.

http://www.tcia.nl

I hope someone can find the problem, I have been commenting out parts of my code to try and see if that would make any differences but have not found any yet.