Category Menu too many items

I have a menu on my home page called Countries. It is a category menu of the countries I have written posts about. The problem is that I have too many countries and the menu items don’t appear to be able to scroll or anything on Windows. On Android I can see the entire menu list. In Windows my list of countries stops at Lithuania. Is there a fix to this. I am using Pinboard which I really like. On Windows the Countries dropdown stops at Lithuania. How do I see the entire list of categories from the menu item?
As a work around, I thought that I might create a manual page that let the user select the country/category that they wanted to see. I can’t see how to insert categories into a page.
Help Thanks.

http://www.roadsaway.com