Bootstrap 4插入符号在打开菜单后的方向更改

Question

我是Bootstrap 4的新手，我有一个带有下拉菜单的导航菜单。它具有指向下方的标准Bootstrap插入标记，该标记会自动添加。

现在，我想在打开导航项的下拉菜单后将方向更改为“向上”。我已经搜索了整个互联网，甚至更多，但是如果不使用真棒字体或变通方法，就找不到适用于Bootstrap 4的可行解决方案。

这是菜单的HTML代码（工作正常），包括下拉菜单项（项目2）：

<nav class="navbar navbar-expand-sm navbar-light">
  <a class="navbar-brand" href="#"><img src="img/logo.svg" width="80" height="80" alt="Logo"></a>
  <button type="button" class="navbar-toggler" data-toggle="collapse" data-target=".navbar-collapse">
    <span class="sr-only"></span>
    <span class="icon-bar"></span>
    <span class="icon-bar"></span>
    <span class="icon-bar"></span>
  </button>
  <div class="collapse navbar-collapse">
    <div class="navbar-nav">
      <a class="nav-item nav-link active" href="#">Item 1<span class="sr-only">(current)</span></a>
      <li class="nav-item dropdown">
        <a class="nav-link dropdown-toggle" href="" data-toggle="dropdown">Item 2</a>
        <div class="dropdown-menu">
          <a class="dropdown-item" href="#">Item 2.1</a>
          <a class="dropdown-item" href="#">Item 2.2</a>
          <a class="dropdown-item" href="#">Item 2.3</a>
        <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="#">Item 2.4</a>
        </div>
      </li>
      <a class="nav-item nav-link" href="#">Item 3</a>
      <a class="nav-item nav-link" href="#">Item 4</a>
    </div>
  </div>
</nav>

CSS或jQuery解决方案都可以，只要这不是解决方法，而是一个不错的干净的Bootstrap解决方案。应该有可能吧？

因此，打开下拉菜单项时，谁能帮助我将插入符号的方向从向下更改为向上？最终有了不错的动画。提前致谢！

Answer 1

您可以像这样简单地旋转它：

.dropdown-toggle[aria-expanded="true"]:after {
  transform: rotate(180deg);
}


/*for the animation*/
.dropdown-toggle:after {
  transition: 0.5s;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script>
<nav class="navbar navbar-expand-sm navbar-light">
  <a class="navbar-brand" href="#"><img src="img/logo.svg" width="80" height="80" alt="Logo"></a>
  <button type="button" class="navbar-toggler" data-toggle="collapse" data-target=".navbar-collapse">
    <span class="sr-only"></span>
    <span class="icon-bar"></span>
    <span class="icon-bar"></span>
    <span class="icon-bar"></span>
  </button>
  <div class="collapse navbar-collapse">
    <div class="navbar-nav">
      <a class="nav-item nav-link active" href="#">Item 1<span class="sr-only">(current)</span></a>
      <li class="nav-item dropdown">
        <a class="nav-link dropdown-toggle" href="" data-toggle="dropdown">Item 2</a>
        <div class="dropdown-menu">
          <a class="dropdown-item" href="#">Item 2.1</a>
          <a class="dropdown-item" href="#">Item 2.2</a>
          <a class="dropdown-item" href="#">Item 2.3</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="#">Item 2.4</a>
        </div>
      </li>
      <a class="nav-item nav-link" href="#">Item 3</a>
      <a class="nav-item nav-link" href="#">Item 4</a>
    </div>
  </div>
</nav>