Silly question, but what is this HTML "property"?

Question

HTML

There is an option with frames, but have they already outlived their own?
I need a "scroll block". I do not know how to explain to you what I need, so the example is in the screenshot.
Here is that block, on the right side of the video which, where is the playlist, that's what I need, I'll call it a scrolling block)

Answer 1

Overflow-y: scroll. ....and then, through JS, it seems that you can play with the sliders of the internal scroll bar