Twenty Seventeen: Sub menu with many items get cut off, doesn't scroll

[kokkieh]

Steps to replicate

1) With Twenty Seventeen active, create a custom menu containing a sub-menu with a high number of items - depending on your screen size, upwards of 14 menu items
2) Publish the menu, and then try to access menu items towards the bottom of the sub-menu.

Result

Some menu items are cut off at the bottom of the screen, and there's no way to have them scroll up to make them visible as the top-level menu for this theme is stuck to the top of the page.

Submenu here has 15 items, and sub-submenu has 5.

Expected

For either the entire menu to scroll upwards, or for the sub-menu itself to be scrollable, but ultimately to be able to see menu items lower down on the sub-menus.

Reported via the ​WordPress.com forums, but confirmed on both WordPress.com and Core sites.

[jameskockelbergh]

Sorry, but creating a submenu with that number of elements is a very bad Idea :(

[karmatosed]

This feels like a bug, not a need for ui-feedback but needs fixing.

[sabernhardt]

Thanks for opening the ticket! The issue was already reported on #40456. If you would like, please add the screenshot and/or any comments there.