Scrollbar for multilevel lists. How to do?

Question

css

Hello. There is a site gb.tmweb.ru in which on screens less than ~ 820px high (laptops) the drop-down list "Product catalog" (in the upper left corner) cannot be accessed to the last items. Accordingly, I tried to scroll for this list. I set height + overflow-y:scroll for the first level list, but then a horizontal scroll appears when hovering over the items in this list.