TwentyEleven: adjusting the dropdown in multi-item menu items

Working on a small site for a local volunteer organization, and while the menu is now working the way I want it to, the dropdowns upon mouseover are oddly spaced.

I’ve tried a number of things in the CSS to resolve this, but haven’t been able to figure out what controls it.

Where in the CSS for TwentyEleven can I find the styling for mouseover dropdowns of the site menu.

The site address: vegestrie.shep.ca

I am working in a child theme and do not need instructions or information regarding the necessity of working in a child theme.

Thanks!