code: @TargetApi(Build.VERSION_CODES.JELLY_BEAN)
      public final void setPopupBackgroundDrawable(final Drawable background) {
          getView().setPopupBackgroundDrawable(background);
      }
docs: Set the background drawable for the spinner's popup window of choices. Only valid in
  MODE_DROPDOWN; this method is a no-op in other modes.
  
  @param background
  Background drawable