react-component-viewer-theme.ts

export class MyAppComponentViewer extends React.Component {
  render() {
    return (
      <ComponentViewer
        registries={registries}
        dropDown={{
          label: 'Brand',
          items: [
            {label: 'Brand One', hotKey: 'Alt 1'},
            {label: 'Brand Two', hotKey: 'Alt 2'}
          ],
          onSelect: this.onBrandSelect
        }}
      />
    );
  }

  private onBrandSelect = (brand: string) => {
    const brandDir = brand.toLocaleLowerCase();
    updateCssRef('stylesheet', brandDir, 'style');
  };
}