如何更改打开的bootstrap下拉列表的背景颜色 - Bootstrap 4

Question

如何更改打开的bootstrap下拉选项的背景颜色。这是代码：

<nav class="navbar navbar-toggleable-sm navbar-inverse bg-faded">
  <button class="navbar-toggler navbar-toggler-right" type="button" data-toggle="collapse" data-target="#navbar6">
        <span class="navbar-toggler-icon"></span>
    </button>
  <a href="#" class="navbar-brand">Title </a>
  <div class="navbar-collapse collapse justify-content-stretch" id="navbar6">
    <ul class="navbar-nav ml-auto">
      <li class="nav-item">
        <a class="nav-link" href="#">About<span class="sr-only">Home</span></a>
      </li>
      <li class="nav-item dropdown">
        <a class="nav-link dropdown-toggle" href="http://example.com" id="navbarDropdownMenuLink" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
          Services
        </a>
        <div class="dropdown-menu" aria-labelledby="navbarDropdownMenuLink">
          <a class="dropdown-item" href="#">Design</a>
          <a class="dropdown-item" href="#">Development</a>
          <a class="dropdown-item" href="#">Consulting</a>
        </div>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">Contact</a>
      </li>
    </ul>
  </div>
</nav>

在bootstrap 3中，我通过以下方式更改了它：

.navbar-default .navbar-nav > .open > a,
.navbar-default .navbar-nav > .open > a:focus,
.navbar-default .navbar-nav > .open > a:hover {
  background: #080808;
}

这是bootstrap 3的标准代码（在bootstrap4中不起作用） 我怎么才在bootstrap 4中做同样的事情？

Answer 1

.navbar .dropdown-menu {
  background-color: #BADA55;
}

/* and this styles the dropdwon trigger link, when open */
.navbar .dropdown.show a { 
  background-color: #BADA55;
}

...足够。

注意.navbar将它限制为菜单，没有它，只要你在.dropdown之后加载你的CSS它就会设置所有bootstrap(.min).csss的样式。

.navbar .dropdown-menu {
  background-color: #BADA55;
}
.navbar .dropdown.show a {
  background-color: #BADA55;
}

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css" rel="stylesheet"/>
<script src="https://code.jquery.com/jquery-3.1.1.slim.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/tether/1.4.0/js/tether.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/js/bootstrap.min.js"></script>

<nav class="navbar navbar-toggleable-sm navbar-light bg-faded">
  <button class="navbar-toggler navbar-toggler-right" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>
  <a class="navbar-brand" href="#">Title</a>

  <div class="collapse navbar-collapse justify-content-stretch" id="navbarSupportedContent">
    <ul class="navbar-nav ml-auto">
      <li class="nav-item active">
        <a class="nav-link" href="#">Home <span class="sr-only">(current)</span></a>
      </li>
       <li class="nav-item dropdown">
    <a class="nav-link dropdown-toggle" href="http://example.com" id="navbarDropdownMenuLink" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
      Services
    </a>
    <div class="dropdown-menu" aria-labelledby="navbarDropdownMenuLink">
      <a class="dropdown-item" href="#">Design</a>
      <a class="dropdown-item" href="#">Development</a>
      <a class="dropdown-item" href="#">Consulting</a>
    </div>
  </li>
      <li class="nav-item">
        <a class="nav-link disabled" href="#">Disabled</a>
      </li>
    </ul>
    <form class="form-inline my-2 my-lg-0">
      <input class="form-control mr-sm-2" type="text" placeholder="Search">
      <button class="btn btn-outline-success my-2 my-sm-0" type="submit">Search</button>
    </form>
  </div>
</nav>

请注意，您当前的选择器都不匹配任何内容，因为您似乎没有将navbar-default类应用于任何元素。

作为一般规则，期望在v4中重构许多类名，这允许更短，更具表现力的语法和更大的整体灵活性。 将v3解决方案应用于v4示例通常被认为是不好的做法，就像期望v2解决方案适用于v3示例一样。

Answer 2

这适用于Bootstrap 4.1.3：

.dropdown-menu {
    background-color: #ff0000;
}