If you take a look at page source, you'll see that the YouTube videos are embedded with a few extra parameters that make the interface (what sometimes used to be called the "chrome" before the browser with this name became popular...) a lot more seamless.

Example video URL (the controls=0, showinfo=0 and playsinline=1 play a role in this):

https://www.youtube.com/embed/ceEE_oYuzS4?autoplay=1&mute=1&...