The admin menu submenus may cover part of the main menu after unfolding.

[azaozz]

Steps to reproduce:

• Go to Settings screen (any submenu).
• Fold the admin menu (so it shows icons only).
• Resize the browser window so the bottom of the menu is near the bottom end of the window.
• Hover on the last menu (usually Settings) to show the submenu.
• Unfold the menu.

Result: the submenus are shifted up covering part of the "main" menu items.

In [20387]:

Reset negative top margin on submenus when folding/unfolding the admin menu, fixes #20380

[20386] belonged on #20374