<nav mat-tab-nav-bar>
  <a mat-tab-link
      routerLink="home"
      routerLinkActive #rla="routerLinkActive"
      [active]="rla.isActive">
      home
  </a>
  <a mat-tab-link
      routerLink="about"
      routerLinkActive #rla="routerLinkActive"
      [active]="rla.isActive">
      about
  </a>
</nav>

<router-outlet></router-outlet>

<a mat-tab-link
      routerLink="about"
      routerLinkActive #rla="routerLinkActive"
      routerLinkActive="active"
      [active]="rla.isActive">
      about
</a>

.active{
}