different types of notifications in GNOME Classic

[Adam Funk]

I'm using GNOME Classic on two computers, and getting different types
of notifications:

A. The notification is a grey box with a little X in a circle in the
   top right corner, which I can click to dismiss it.

B. The notification has a black background, and it temporarily
   disappears when I move the pointer to it, then annoyingly comes
   back.  AFAICT there is no way to make it go away until it times
   out.

I want to use A on both machines, & so does a colleague of mine.


I don't know what these options are called, so I haven't had any
success googling for help.  Can anyone tell me the magic words, or
where to configure this?

Thanks,
Adam