I coded along with Wes Bos drum machine tutorial but my code is not working right. The following function is not executed:

function removeTransition(e) {
    if (e.propertyName !== 'transform') return;
    this.classList.remove('playing');
  }

I can't figure out why. I think the error has to be somewhere in the html but I just can not find it. You can find the whole code on this repo https://github.com/BorisKarl/drum-machine. Any help is appreciated. Thank you!