code: private void updateDisplayModeIcon() {
          FontAwesomeIcon icon = FontAwesomeIcon.CALENDAR;
          if (getDisplayMode().equals(DisplayMode.GRID)) {
              icon = FontAwesomeIcon.CALENDAR_ALT;
          }
  
          final Text graphic = FontAwesomeIconFactory.get().createIcon(icon);
          graphic.getStyleClass().addAll("button-icon", "display-mode-icon");
          displayModeButton.setGraphic(graphic);
      }
docs: /*
  Sets the graphic node on the display mode button based on the current display
  mode (column or grid).