I've found part of this code in one of my old backups (like a 'dinosaur old' backups). And I decided to use that as a valentine card for my wife. So I rewrited animation part, added some css, html to make it works as a standalone website.
Originally heart animation was partially hidden under the black background. I decided that I like white version more - but if you really, really want it 'fade to black' (no pun intended) just change the background colour.
The final results you can see: HERE.
Have fun!