text: const keys = Array.from(document.querySelectorAll('.key'));
  keys.forEach(key => key.addEventListener('transitionend', removeTransition));
  window.addEventListener('keydown', playSound);
  
  function removeTransition(e) {
      if (e.propertyName !== 'transform') return;
      e.target.classList.remove('playing');
  }
  
  function playSound(e) {
      const audio = document.querySelector(`audio[data-key="${e.keyCode}"]`);
      const key = document.querySelector(`div[data-key="${e.keyCode}"]`);
      if (!audio) return;
  
      key.classList.add('playing');
      audio.currentTime = 0;
      audio.play();
  }