adsk-forge-LevelSectionPanel-step11

createUI() {
    const viewer = this.viewer;
    const lvlSectionPanel = new LevelSectionPanel( viewer, 'Level Section' );

    viewer.addPanel(lvlSectionPanel);
    this.panel = lvlSectionPanel;

    const lvlSectionButton = new Autodesk.Viewing.UI.Button( 'toolbar-adnLevelSectionsTool' );
    lvlSectionButton.setToolTip( 'Level Sections' );
    lvlSectionButton.setIcon( 'adsk-icon-plane-y' );
    lvlSectionButton.onClick = () => {
        lvlSectionPanel.setVisible(!lvlSectionPanel.isVisible());
    };

    // ...
    const subToolbar = new Autodesk.Viewing.UI.ControlGroup( 'toolbar-adn-tools' );
    subToolbar.addControl( lvlSectionButton );
    this.subToolbar = subToolbar;
    viewer.toolbar.addControl( this.subToolbar );

    lvlSectionPanel.addVisibilityListener(( visible ) => {
       if ( visible )
           viewer.onPanelVisible( lvlSectionPanel, viewer );

       lvlSectionButton.setState( visible ? Autodesk.Viewing.UI.Button.State.ACTIVE : Autodesk.Viewing.UI.Button.State.INACTIVE );
    });
}