app.component.html
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			<div [class]="theme">
			<mat-card>
			<mat-select placeholder="Standard Theme"
			[(ngModel)]="theme"
			(change) = "onThemeChange()">
			<mat-option value="standard-theme">Standard</mat-option>
			<mat-option value="green-theme">Green</mat-option>
			</mat-select>
			</mat-card>
			<mat-card>
			<h1>Der späte Nietzsche, Manuskripte 1885-1889</h1>
			</mat-card>
			<app-main-menu-component></app-main-menu-component>
			<router-outlet></router-outlet>
			<!--<div style = "padding: 60px;"><app-bergwerke></app-bergwerke></div>-->
			</div>

NietzscheBeta/nietzsche-beta-app/src/app/app.component.htmlef367fd4caaecrossref-editor