<!-- sidenav.component.html -->
<mat-sidenav-container>
  <mat-sidenav mode="side" opened>
    <a>teste</a>
  </mat-sidenav>
  <mat-sidenav-content>
    <!-- componentes aqui -->
    <ng-content></ng-content>
  </mat-sidenav-content>
</mat-sidenav-container>

<!-- index.component.html -->
<app-top-menu>
  <app-sidenav></app-sidenav>
</app-top-menu>