3분 안에 부트스트랩 드롭다운 메뉴를 이해하도록 안내합니다.

<div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
        示例<span class="caret"></span>
        </button>
        <ul class="dropdown-menu">
          <li><a href="#">列表1</a></li>
          <li><a href="#">列表2</a></li>
          <li role="separator" class="divider"></li>
          <li><a href="#">列表3</a></li>
      </ul>
    </div>

<div class="btn-group">
    <button type="button" class="btn btn-danger">示例</button>
    <button type="button" class="btn btn-danger dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
      <span class="caret"></span>
      <span class="sr-only">示例</span>//为了残障人士设计，不影响正常的阅读，屏幕阅读器能识别并阅读出来
    </button>
    <ul class="dropdown-menu">
        <li><a href="#">列表1</a></li>
        <li><a href="#">列表2</a></li>
        <li role="separator" class="divider"></li>
        <li><a href="#">列表3</a></li>
    </ul>
</div>

<div class="btn-group">
        <button class="btn btn-default btn-lg dropdown-toggle" type="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
        大尺寸菜单<span class="caret"></span>
        </button>
        <ul class="dropdown-menu">
            <li><a href="#">列表1</a></li>
            <li><a href="#">列表2</a></li>
            <li role="separator" class="divider"></li>
            <li><a href="#">列表3</a></li>
        </ul>
    </div>
      
      <div class="btn-group">
        <button class="btn btn-default btn-sm dropdown-toggle" type="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
        中等尺寸菜单<span class="caret"></span>
        </button>
        <ul class="dropdown-menu">
            <li><a href="#">列表1</a></li>
            <li><a href="#">列表2</a></li>
            <li role="separator" class="divider"></li>
            <li><a href="#">列表3</a></li>
        </ul>
    </div>
      
      <div class="btn-group">
        <button class="btn btn-default btn-xs dropdown-toggle" type="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
        小尺寸菜单<span class="caret"></span>
        </button>
        <ul class="dropdown-menu">
            <li><a href="#">列表1</a></li>
            <li><a href="#">列表2</a></li>
            <li role="separator" class="divider"></li>
            <li><a href="#">列表3</a></li>
        </ul>
    </div>