Patrick Brosset, writing for A List Apart, digging into the Window Controls Overlay for Progressive Web Apps:
At the end of the day though, PWAs on desktop are constrained to the window they appear in: a rectangle with a title bar at the top.
What if we could think outside this box, and reclaim the real estate of the app’s entire window? Doing so would give us a chance to make our apps more beautiful and feel more integrated in the operating system.
Once activated from the manifest, you get to define an
app-region and can also use these Environment Variables in your CSS: