MacBook Pro minimize button missing

I have a MacBook Pro running Lightroom 6 that was working fine - the three colored buttons at the top of the screen were there, and could minimize Lightroom as needed..

Today I clicked on the green button to maximize the screen.  Worked, but there is no obvious way to switch it back.  The place where the three buttons might appear seems to be covered by the MacBook menu line at the top of the screen.

I've been searching the forums and reading, and while some people find answers, others don't.

I read where typing "F" would cycle the screen through three (or four someplace else) modes, where one of them would allow me to un-do the maximizing.  In my case, the "F" switched back and forth between what I see now, and then enlarging one image to fill the entire screen.

I'd like to think that if I created this problem by simply clicking on the green maximize button, there must be some way to un-click it.....   but I can't find the buttons in order to click on it again, so I need something else. 

Someone suggested I change my "screen modes" under the view menu, but the choices he suggested were not there.