thanks for your answers!
I updated my code (codepen in the first entry)
Yes, sliding seems to be a better idea than scrolling, but I can't achieve it. Basically I can't achieve two things:
1. Scrolling/moving the content itself - when I tried to do this, I was moving the entire element, not its content.
2. I don't know how to stop the next tab from entering until the content moves to the bottom
For example, I added opacity there, it ends when the next tab is at the top, I would like the opacity to be done on scrolling to 0 and only then the next tab appears.
Ultimately, it is not supposed to be about opacity, but about moving/scrolling the content down.
https://codepen.io/Rafa-Olejarz-the-flexboxer/pen/LYqJXej