Angular Material Theming - overlay handling

app.component.ts

import { OverlayContainer} from '@angular/cdk/overlay';

export class AppComponent implements OnInit {

  // use this to set correct theme class on app holder
  // eg: <div [class]="themeClass">...</div>
  themeClass: string;

  overlayContainer;

  constructor(
    private overlayContainer: OverlayContainer
  ) {}

  ngOnInit(): void {
    // subscribe to some source of theme change events, then...
    this.themeClass = newThemeClass;
    this.overlayContainer.themeClass = newThemeClass;
  }

}