What is the name of the appearance of the menu after the page with the button?

Question

css

Good day.
In the past, we've often seen sites that have a "welcome screen" with a button that scrolls to the next screen with a "sticky" navigation bar. The first screen after that disappeared forever. I can't find any live examples or examples of implementation (the principle is clear, but it turns out something "not right"). Google was not blocked for me, it googles so-so - endless sticky panels and that's it. Maybe I'm typing the request very crookedly, I don't know.
It would be very helpful if someone would either throw off the name of this technique, or examples of implementation. And then at this point we slow down very strongly and for a long time.

Answer 1

The welcome screen is initially visible, the rest of the page is not.
By pressing the button, the visibility changes places. Or the same with z-index.

Answer 2

Maybe we are talking about pop-up windows.