Thanks for the display: none; tweak, @dax. That helped on desktop view, which now looks like this.
However, mobile view still shows the Activity and Messages options in the drop-down list, and frustratingly, the empty white space that was there before (which must be default theme or environmental related).
Do you know why the CSS would work on desktop view and not mobile view? And do you know if there’s a way to use a wildcard in the CSS to apply the display: none; code to all groups instead of going one-by-one?