text: const panels = document.querySelectorAll('.panel');
  
  function toggleOpen() {
    this.classList.toggle('open');
  }
  function toggleActive(e) {
    if (e.propertyName.includes('flex')) {
      this.classList.toggle('open-active');
    }
  }
  
  panels.forEach(panel => panel.addEventListener('click', toggleOpen));
  panels.forEach(panel => panel.addEventListener('transitionend', toggleActive));
  