function getDeepActiveElement() {
  let host = document.activeElement || document.body;
  while (host && host.shadowRoot && host.shadowRoot.activeElement) {
    host = host.shadowRoot.activeElement;
  }
  return host;
}
Returns the activeElement, even when they are inside a shadowRoot.
(If an element in a shadowRoot is focused, document.activeElement
returns the shadowRoot host.

@returns {Element}