NgbDropdown custom arrow for dropup button

I am trying to have different arrows for toggle drop-up button. how can we use different arrows? when its showing drop up menu, then it should have down arrow and when it doesn't show any menu then it should have up arrow

 <div class="col text-right">
    <div ngbDropdown placement="top-right" class="d-inline-block">
      <button class="btn btn-outline-primary" id="dropdownBasic2" ngbDropdownToggle>Toggle dropup</button>
      <div ngbDropdownMenu aria-labelledby="dropdownBasic2">
        <button class="dropdown-item">Action - 1</button>
        <button class="dropdown-item">Another Action</button>
        <button class="dropdown-item">Something else is here</button>
      </div>
    </div>
  </div>
</div>