Gallery background?

I attend a Zoom, in which once we were in Gallery Mode, the background was changed.  It was a nice floral background.  Our "gallery" of attendees was only 2.  The boxes (of attendees) were centered and had round corners.  As a participant, as well as the owner of the zoom, our "view" or  background remained the same.  The background in my view was blurred, the background in her view was her home office.  I would like to know how to change the Gallery background.  Would love to round the corners of the gallery tiles as well.  Thank you.  @gallery