This has been discovered during the review of #602

In #602, the header of the user menu submenu was made fully clickable to ease the integration of the smart submenu into the user menu.
However, due to this change, the original hover effect in the language menu (and the smart submenus in the user menu in general) got lost.

This is how it looks like in Boost when hovering over the arrow icon in the header:

This is how it looks like in Boost Union when hovering over the the header:

It would be great if Boost Union could use the same hover effect on the arrow icon as well as the original black header color in the submenu even though the full header is now clickable.