Add cursor: pointer; to [role="button"] to fix #371

* Address cursor inconsistency between `button` and `[role="button"]`
* Work around Safari element clickability issue, at least for
  button-ish widgets with `[role="button"]`. Such widgets should have
  the role for proper accessibility anyway. See also
  https://developer.mozilla.org/en-US/docs/Web/Events/click#Safari_Mobile