If you hover over the nav buttons, you will see the dropdown links. On mobile devices you have to tap on them, and a close button will appear at the bottom of each dropdown (not visible on desktops/laptops because they are not necessary there).
To edit the sub-buttons, you need to change the overflow on the buttons-container from hidden to visible. Just remember to set it back when you are done.
The 'desktop-down' version has been made 'fixed' to the top of the page.