rtt-modal-focus-open-close.tsx

// resolve focus on opening and closing
useEffect(() => {
  if (open) {
    previousFocus.current = (document.activeElement as HTMLElement) ?? null;
    nextFocus(getFocusableElements(container.current));
  } else {
    previousFocus.current?.focus?.();
    previousFocus.current = null;
  }
}, [open, portal]);

// ... in our key listener, manage `tab` presses
switch (e.key) {
  case "Tab": {
    e.preventDefault();
    nextFocus(getFocusableElements(container.current), !e.shiftKey);
    break;
  }
 ...
}