Mobile sidebar menus overlap sidebar footer

Problem/Motivation

I thought there was an issue for this already, but couldn't find it.

A longer submenu (3rd level) in the "mobile" version of the sidebar will lengthen the main / menu section of the sidebar such that it overlaps the sidebar footer.

Something with the backgrounds or z-index causes the content of both sections to be visible at the same time and overlapping.

Here's a screenshot:

Steps to reproduce

1. Log in as admin.
2. Adjust the viewport to less than 1020px wide and approximately 780px high.
3. Expand the sidebar.
4. Expand the Configuration menu.
5. Expand the Development submenu.

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet