app.component.html

<div fxLayout="column" fxFlexFill style="background-image: url(/assets/background.jpg); background-repeat: repeat;" >
  <app-header>
  </app-header>
  <div fxFlex>
    <router-outlet></router-outlet>
  </div>
  <app-footer>
    <mat-toolbar color="primary">
      <span>Footer</span>
    </mat-toolbar>
  </app-footer>
</div>