Stranger Things Spotify playlist easter egg

I have just seen that on stranger things spotify playlist there is an animation linked to the TV series atmosphere, go on this page to see it http://ift.tt/2yQy0Zi

Don't move your mouse and it will trigger after music is playing.

I was wondering how this animation is displayed, it has triggered my curiosity, so if anyone have some answer I would be really interested knowing it !

Thanks in advance !