How do I "activate" the viewer window in FCPX without reaching for the mouse?

Hopefully simple question here...

If I hit Command+ or command- in I will zoom in or out of the storyline or the viewer depending on what I last did. This is what i mean by "Active".

If I start zooming out with a keyboard shortcu only to find the wrong area is active, how do i switch to another active area so the zoom affects the correct window pane without having to reach for the mouse?

Thanks 🙂