const elmRef = document.querySelector('.faq-overlay .mat-dialog-container') || document.body;
fromEvent(elmRef, 'scroll')
  .pipe(
    takeUntil(this.unsubscribe),
    debounceTime(200)
  )
  .subscribe(() => {
    this.isScrollButtonVisible = elmRef.scrollTop > 100;
    this.cdRef.detectChanges();
  });