Zooming out in Mask module

[Barton5C39]

If I am in the mask module and have used Ctrl-Shift (Windows) plus dragging the mouse right or left to zoom in and out, and I've zoomed in and want to revert to full screen (equivalent to Ctrl + 0 in PS) - how can I do that?  If someone knows a link where all the zoom adn screen commands in various modules (mainly Develop and Mask) are listed that'd be helpful.  Thank you.  

[JohanElzenga]

You can click on 'Fit' at the top of the preview in the left panel.

[Per Berntsen · Accepted solution]

Pressing Z will toggle Fit view and the previous view.

There's a list of shortcuts here: https://helpx.adobe.com/lightroom-classic/help/keyboard-shortcuts.html

It lists the Z shortcut under Keys for working in the Develop module, but as far as I can tell, it works everywhere.

You can also press the spacebar, but it doesn't work in Masking.