Make weird dropdown menu responsive header CSS rules more specific

Problem/Motivation

They are generally making problems for small screens because they are removing bg and border of dropdown menu and doing some other smaller inner layout changes. Not sure why any more, missing comment in code, probably the idea was to make dropdown menu in responsive sidebar menu items looks more like regular menu items, but this really does not make a lot of sense.

For now Iet's make this rules more specific - active only for .navmenu.in parent and add a comment to probably remove this rules in future.