NgbDropdown下拉按钮的自定义箭头

Question

我尝试使用不同的箭头来切换下拉按钮。 我们如何使用不同的箭头？当其显示下拉菜单时，则应具有向下箭头；当不显示任何菜单时，则应具有向上箭头

 <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>