message: style(selection): fix typing
diff: @@ -73,8 +73,12 @@ message.addListener(msg => {
  }
  })
  +interface PostMessageEvent extends MessageEvent {
  + data: PostMsgSelection
  +}
  +
  /** Pass through message from iframes */
  -window.addEventListener('message', ({ data, source }: { data: PostMsgSelection, source: Window | null }) => {
  +window.addEventListener('message', ({ data, source }: PostMessageEvent) => {
  if (data.type !== PostMsgType.Selection) { return }
  // get the souce iframe
  