Enabling scrolling or scaling of primary menu

Hello, our website is at http://presentmomentphotography.ca. I notice that the primary menu on the left-hand side doesn't scroll. When testing on desktop, if I start increasing the font size in the browser, at some point the bottom menu items start disappearing. The main content area does scroll and I'm able to see all of it. However, I am not able to access the menu items that have disappeared. What can I try to solve this? Thanks in advance.