collapse.html

  <p>
    <button type="button" class="btn btn-outline-primary" (click)="isCollapsed = !isCollapsed"
            [attr.aria-expanded]="!isCollapsed" aria-controls="collapseExample">
      Toggle
    </button>
  </p>
  <div id="collapseExample" [ngbCollapse]="isCollapsed">
    <div class="card">
      <div class="card-block">
        You can collapse this card by clicking Toggle
      </div>
    </div>
  </div>