How to switch to fullscreen?

I would like to enlarge the window of the app to the size of the browser window. I couldn't find a solution for that as I read it is up to the browser and not (easily) doable out of R.
Nevertheless, the most deployed apps I see are operating in fullscreen. Is there maybe meanwhile a feature for it?
Or can we implement a button or so the customer has to click to toggle between fullscreen and windowed?

Fullscreen is not really fullscreen, I just want to make use of the entire window within the browser.

Thank you!