html - 下拉列表显示在父 div 后面

Question

我有一个包装 div，在那个 div 里面有一些带有下拉按钮的按钮，包装应该有一个最大高度和一个自动滚动。

问题是如果我点击一个按钮，现在下拉菜单总是放在包装器后面，有没有办法让下拉菜单放在包装器的顶部

jsbin link

.bs-example
{
  display: flex;
  flex-direction: column;
    margin: 30px;
    max-height: 100px;
    border: 1px solid #F00;
    overflow: auto;
}

<link href="http://netdna.bootstrapcdn.com/bootstrap/3.0.0/css/bootstrap.min.css" rel="stylesheet"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<script src="http://netdna.bootstrapcdn.com/bootstrap/3.0.0/js/bootstrap.min.js"></script>

<div class="bs-example">
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
    </div>

Answer 1

你在这里有一个工作片段

.bs-example
{
  display: flex;
  flex-direction: column;
    margin: 30px;
    max-height: 100px;
    border: 1px solid #F00;
    overflow: auto;
}
.dropdown-menu {
    position: fixed !important;
    top: auto !important;
}

<link href="http://netdna.bootstrapcdn.com/bootstrap/3.0.0/css/bootstrap.min.css" rel="stylesheet"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="http://netdna.bootstrapcdn.com/bootstrap/3.0.0/js/bootstrap.min.js"></script>
<div class="bs-example">
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
    </div>

You can set left as well for align to left of div, I also use !important; to override bootstrap default styles.