You can define your own arbitrary HTML < /> tags and style them or use JS with them in modern browsers (which is what hstack and vstack are, which seems to be inspired by the pylon framework and SwiftUI).

If you need to support really old browsers than using an HTML5 shiv will be sufficient for any <tag /> to work:

https://johnresig.com/blog/html5-shiv/

There's a longer discussion here about pros/cons:

https://stackoverflow.com/questions/16867332/html5-why-not-u...

I have a feeling this is one of those things that will become more common with this broader support for HTML5 and web components but at the moment it's not very common and there are some debates on whether you should break web standards/specs.