ng-custom-properties#layout-buttons.ts

@Component({
  selector: 'app-root',
  template: `
  <app-card></app-card>
  
  <button (click)="theme = indigoPinkTheme">Indigo Pink</button>
  <button (click)="theme = pinkBlueGrayTheme">Pink BlueGray</button>
  <button (click)="theme = deepPurpleAmberTheme">Deep Purple Amber</button>
  <button (click)="theme = randomTheme()">?</button>
  `,
})
export class AppComponent {
  // ... 
}