Bootstrap學習4

下拉菜單：

<div class="dropdown">
    <button class="btn btn-success dropdown-toggle"  type="button"  id="dropdownmenu" data-toggle="dropdown">
    下拉菜單
    <span class="caret"></span>
    </button>
    <ul class="dropdown-menu dropdown-menu-right(left)" role="menu" aria-labelledby="dropdownMenu1">
    <li role="presentation" class="dropdown-header">第一部分菜單頭部</li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜單項</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜單項</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜單項</a></li>
    <li role="presentation" class="divider"></li>
    <li role="presentation" class="dropdown-header">第二部分菜單頭部</li>
    <li role="presentation"  class="active"><a role="menuitem" tabindex="-1" href="#">下拉菜單項</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜單項</a></li>
    <li role="presentation" class="disabled"><a role="menuitem" tabindex="-1" href="#">下拉菜單項</a></li>
    </ul>
</div>