Overlapping elements in menu

Hello!

Here is the URL to my site: http://www.chickatay.com

I am using the Optimizer Pro theme for my site. On the navigation menu, certain elements overlap, making it so that people are not able to see the pages nested under a category.

To be more specific, under capabilities > fixed & rotor training , if you hover over International Flight Training the pages nested under are hidden behind the list of pages underneath Domestic Flight Training. My customers have told me that they were unable to navigate to certain pages for this reason (they can’t see them on the menu because of the overlap).

How can I fix this?