How do I use gmail (or whatever) as a chrome app in windows 10 that doesn't close, just minimizes as a background app, when I click the top-right x?

I have my google calendar and gmail setup as apps (they're chrome app shortcuts you create in Chrome using settings > more tools > create application shortcuts...) in my taskbar in Windows 10. But I'd like to treat them as background apps that stay open whether I click the minimize or close buttons at the top right.

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