<p>[Press any key]</p>

body {
  padding: 20px;
  font-weight: bold;
  font-size: 5em;
  text-align: center;
}

// Press any key and the result will display on the page.
// Make sure your cursor is focused in the preview window first.
window.addEventListener('keydown', function (e) {
  document.querySelector('p').innerHTML = `You pressed ${e.key}`;
}, false);