Bootstrap里按钮的尺寸怎么设置呢？

按钮式下拉菜单适用所有尺寸的按钮。 实例如图：

代码如下：

<! -- Large button group -->
<div class="btn-group">
  <button class="btn btn-default btn-lg dropdown-toggle" type=" button" data-toggle= "dropdown" aria-haspopup="true" aria-expanded="false">
    Large button <span class="caret"></span>
  </button>
  <ul class="dropdown-menu">
...
  </ul>
</div>

<!-- Small button group -->
<div class="btn-group">
  <button class="btn btn-default btn-sm dropdown-toggle" type="button”data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
    Small button <span class="caret"></span>
  </button>
  <ul class="dropdown-menu">
    ...

  </ul>
</div>

<!--Extra small button group -->
<div class="btn-group">
  <button class="btn btn-default btn-xs dropdown-toggle" type=" button" data-toggle= "dropdown" aria-haspopup="true" aria-expanded="false"">
    Extra small button <span class="caret"></span>
  </button>
  <ul class="dropdown-menu">
  ...
  </ul>
</div>