chrome/browser/resources/options/alert_overlay.html

<div id="alertOverlay" class="page" hidden>
  <div class="close-button"></div>
  <h1 id="alertOverlayTitle"></h1>
  <div class="content-area">
    <div id="alertOverlayMessage"></div>
  </div>
  <div class="action-area">
    <div class="button-strip">
      <button id="alertOverlayCancel" type="reset"></button>
      <button id="alertOverlayOk" class="default-button" type="submit"></button>
    </div>
  </div>
</div>