Bootstrap按钮下拉菜单组件详解

<div class="btn-toolbar" role="toolbar">
 <div class="btn-group">
  <button type="button" class="btn btn-default">1</button>
  <button type="button" class="btn btn-default">2</button>
  <button type="button" class="btn btn-default">3</button>
  <button type="button" class="btn btn-default">4</button>
  <button type="button" class="btn btn-default">5</button>
  <button type="button" class="btn btn-default">6</button>
 </div>
 <div class="btn-group">
  <button type="button" class="btn btn-default">7</button>
  <button type="button" class="btn btn-default">8</button>
 </div>
 <div class="btn-group">
  <button type="button" class="btn btn-default">9</button>
 </div>
 </div>

<div class="btn-group">
 <button class="btn btn-default dropdown-toggle" data-toggle="dropdown">
  按钮下拉菜单
  <span class="caret"></span>
 </button>
 <ul class="dropdown-menu">
  <li><a href="#">菜单列表1</a></li>
  <li><a href="#">菜单列表2</a></li>
  <li><a href="#">菜单列表3</a></li>
  <li><a href="#">菜单列表4</a></li>
  <li><a href="#">菜单列表5</a></li>
 </ul>
 </div>

.btn-group .dropdown-toggle:active,
.btn-group.open .dropdown-toggle {
 outline: 0;
}
.btn-group > .btn + .dropdown-toggle {
 padding-right: 8px;
 padding-left: 8px;
}
.btn-group > .btn-lg + .dropdown-toggle {
 padding-right: 12px;
 padding-left: 12px;
}
.btn-group.open .dropdown-toggle {
 -webkit-box-shadow: inset 0 3px 5px rgba(0, 0, 0, .125);
  box-shadow: inset 0 3px 5px rgba(0, 0, 0, .125);
}
.btn-group.open .dropdown-toggle.btn-link {
 -webkit-box-shadow: none;
  box-shadow: none;
}

<button class="btn btn-default dropdown-toggle" data-toggle="dropdown">
 按钮下拉菜单
 <span class="caret"></span>
</button>

.caret {
 display: inline-block;
 width: 0;
 height: 0;
 margin-left: 2px;
 vertical-align: middle;
 border-top: 4px solid;
 border-right: 4px solid transparent;
 border-left: 4px solid transparent;
}