How to make menu scroll vertically?

Question

css

Hello!
There is a standard menu, a submenu appears on hover, then a submenu, etc., nothing complicated. Each submenu has a fixed width and height. The task was set that if there are a lot of items in any of the submenus, then a scroll appears (vertically, naturally).
How can I do that? At least approximately, but it does not work out in any way.
PS only without plugins, by your own means (html, css, javascript or jquery)
Thanks in advance :)

Answer 1

codepen.io/anon/pen/NpQmex