code: @TargetApi(VERSION_CODES.KITKAT)
      public static void showSystemUI(Activity activity) {
          View decorView = activity.getWindow().getDecorView();
          decorView.setSystemUiVisibility(
                  View.SYSTEM_UI_FLAG_LAYOUT_STABLE
                          | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
                          | View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
          );
      }
docs: except for the ones that make the content appear under the system bars.