function addNumberButtons() {
  const numberButtons = document.querySelectorAll('input[type=\'number\']')
  numberButtons.forEach(input => Object.entries({
    '<': 'stepDown',
    '>': 'stepUp'
  }).reduce((before, [text, step]) => {
    const btn = document.createElement('button')
    btn.textContent = text
    btn.addEventListener('click', () => {
      input[step]()
      input.dispatchEvent(changeEvt)
    })
    return input.parentNode.insertBefore(btn, before.nextSibling)
  }, input))
}