How to limit fullscreen in a window?

Question

YouTube

On many sites, like youtube or tvrain, you can enable full screen video, as many people know. And at the same time, the video frame covers the entire screen, including the taskbar. Is there any universal way to make the video expand to the entire browser tab area, say chrome?
One time youtube turned around like this, it happened on its own, then it stopped on its own, I still don’t understand why.

Answer 1

You cannot change the behavior of fullscreen.
But you can use some browser plugin that can work with YouTube videos and resize the player, for example