03.accordion.component.html

<div class="accordion">
  <div class="accordion-head">
    <button (click)="isOpen = !isOpen">{{ isOpen ? "-" : "+" }}</button>
  </div>
  <hr />
  <div *ngIf="isOpen" class="accordion-content">
    <ng-container *ngIf="accordionBodyRef; else eagerBody">
      <ng-container *ngTemplateOutlet="accordionBodyRef"></ng-container>
    </ng-container>
    <ng-template #eagerBody>
      <ng-content select="[accordionBody]"></ng-content>
    </ng-template>
  </div>
</div>