<div class="dropdown">
  <button type="button" class="btn btn-primary dropdown-toggle" data-toggle="dropdown">
    Dropdown button
  </button>
  <div class="dropdown-menu dropdown-menu-right">
    <div class="dropdown-header">Dropdown header 1</div>
    <a class="dropdown-item" href="#">Link 1</a>
    <a class="dropdown-item" href="#">Link 2</a>
    <a class="dropdown-item" href="#">Link 3</a>
    <div class="dropdown-divider"></div>
    <div class="dropdown-header">Dropdown header 1</div>
    <a class="dropdown-item" href="#">Link 1</a>
  </div>
</div>

.dropup  设置上拉