Confused about sharing from iOS to Smart TV....

I'm very confused about sharing my screen from my iPad and iPhone. So:

If I open YouTube or Netflix, I press the "cast" button (the square one below with the wifi symbol in the corner), my TV shows, I select my TV and the content plays.

But, I want to share a browser window in this way and don't know how to get that to work. Screen mirroring from the control centre does not show my TV, I then wondered it it used chromecast technology but the apps I tried with that don't seem to work either.

Can someone tell me how I can get my iOS browser screen (don't care if it's safari, chrome or firefox) on my TV screen or at least explain why it works from YouTube but not with any browser I tried?

Thank you.