src/app/homepage/auth-card/auth-card.component.html

<section class="auth-popup">
  <div class="auth-card" [class.flipped]="isFlipped">
    <div class="card-inner">
      <div class="card-front">
        <!-- Embed sign-in content directly -->
        <ng-container *ngTemplateOutlet="signInTemplate"></ng-container>
      </div>
      <div class="card-back">
        <!-- Embed sign-up content directly -->
        <ng-container *ngTemplateOutlet="signUpTemplate"></ng-container>
      </div>
    </div>
  </div>

  <!-- Templates passed in from parent component -->
  <ng-content select="[signInTemplate]"></ng-content>
  <ng-content select="[signUpTemplate]"></ng-content>
</section>