我有一个导航栏，该菜单栏的中心对齐菜单项，其中一些是下拉菜单。导航栏和下拉菜单的宽度为100％，但我希望下拉菜单的宽度为60％，并且仍居中对齐。
HTML：
<div class="container">
<div class="row">
<div class="col-12">
<nav class="navbar fixed-top navbar-expand-lg navbar-dark" style="background-color: #8B0000;">
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent2" aria-controls="navbarSupportedContent2" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse" id="navbarSupportedContent2">
<ul class="navbar-nav mx-auto">
<li class="nav-item dropdown megamenu-li">
<a href="#" class="nav-link dropdown-toggle" aria-haspopup="true" id="navitem-1" data-toggle="dropdown">
Drop down
</a>
<div class="dropdown-menu megamenu" aria-labelledby="navitem-1">
<div class="row">
<div class="col-sm-6 col-lg-3">
<a class="dropdown-item" href="#">Item</a>
<a class="dropdown-item" href="#">Item</a>
</div>
<div class="col-sm-6 col-lg-3">
<a class="dropdown-item" href="#">Item</a>
<a class="dropdown-item" href="#">Item</a>
</div>
</div>
</div>
</li>
<li class="nav-item">
<a href="#" class="nav-link">
Item
</a>
</li>
<li class="nav-item">
<a href="#" class="nav-link">
Item
</a>
</li>
</ul>
</div>
</nav>
</div>
</div>
</div>
CSS：
.megamenu-li {
position: static;
}
.megamenu {
position: absolute;
width: 100%;
left: 0;
right: 0;
padding: 15px;
}
请在此处查看演示：https://jsfiddle.net/stackoverflow123/53fn2kop/
减小.megamenu的宽度会按预期减小下拉菜单面板，但会阻止其居中对齐。
提前谢谢
答案 0 :(得分：0)
我设法达到了您的目标（如果我理解正确的话），主要是将下一种样式应用于dropdown-menu，但仅在特定的引导断点（LG）上删除了所有风格：
.custom-dropdown {
position: fixed !important;
width: 60vw;
left: 20vw !important;
top: 45px !important;
}
此外，我删除了外部的row和col-12并将container替换为container-fluid，并对dropdown-menu上的项目进行了一些小的更改所以它们看起来居中。您可以在下面进行检查：
@media (min-width: 992px)
{
.custom-dropdown {
position: fixed !important;
width: 60vw;
left: 20vw !important;
top: 45px !important;
}
}<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.6/umd/popper.min.js" integrity="sha384-wHAiFfRlMFy6i5SRaxvfOCifBUQy1xHdJ/yoi7FRNXMRBu5WHdZYu1hA6ZOblgut" crossorigin="anonymous"></script>
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.2.1/css/bootstrap.min.css" integrity="sha384-GJzZqFGwb1QTTN6wy59ffF1BuGJpLSa9DkKMp0DgiMDm4iYMj70gZWKYbI706tWS" crossorigin="anonymous">
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.2.1/js/bootstrap.min.js" integrity="sha384-B0UglyR+jN6CkvvICOB2joaf5I4l3gm9GU6Hc1og6Ls7i6U/mkkaduKaBhlAXv9k" crossorigin="anonymous"></script>
<div class="container-fluid">
<nav class="navbar fixed-top navbar-expand-lg navbar-dark" style="background-color: #8B0000;">
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent2" aria-controls="navbarSupportedContent2" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse" id="navbarSupportedContent2">
<ul class="navbar-nav mx-auto">
<li class="nav-item dropdown">
<a href="#" class="nav-link dropdown-toggle" aria-haspopup="true" id="navitem-1" data-toggle="dropdown">
Drop down
</a>
<div class="dropdown-menu custom-dropdown" aria-labelledby="navitem-1">
<div class="row">
<div class="col-6 text-center">
<a class="dropdown-item" href="#">Item</a>
<a class="dropdown-item" href="#">Item</a>
</div>
<div class="col-6 text-center">
<a class="dropdown-item" href="#">Item</a>
<a class="dropdown-item" href="#">Item</a>
</div>
</div>
</div>
</li>
<li class="nav-item dropdown">
<a href="#" class="nav-link dropdown-toggle" aria-haspopup="true" id="navitem-2" data-toggle="dropdown">
Drop down 2
</a>
<div class="dropdown-menu custom-dropdown" aria-labelledby="navitem-2">
<div class="row">
<div class="col-6 text-center">
<a class="dropdown-item" href="#">Item</a>
<a class="dropdown-item" href="#">Item</a>
</div>
<div class="col-6 text-center">
<a class="dropdown-item" href="#">Item</a>
<a class="dropdown-item" href="#">Item</a>
</div>
</div>
</div>
</li>
<li class="nav-item">
<a href="#" class="nav-link">Item</a>
</li>
<li class="nav-item">
<a href="#" class="nav-link">Item</a>
</li>
<li class="nav-item">
<a href="#" class="nav-link">Item 333</a>
</li>
<li class="nav-item">
<a href="#" class="nav-link">Item 99999</a>
</li>
</ul>
</div>
</nav>
</div>
答案 1 :(得分：0)
以@Shidersz方法为基础，我想要一个带有列的全角居中导航栏。我使用了bootstrap 4，并添加了一个custom-dropdown类。这需要将导航栏固定在顶部或滚动没有预期的行为。
.custom-dropdown {
position: fixed !important;
width: 100vw;
left: 0vw !important;
top: 50px !important;
}
<nav class="navbar fixed-top navbar-expand-sm navbar-toggleable-sm navbar-light bg-white border-bottom box-shadow mb-5">
<div class="container">
<a class="navbar-brand">Full Width Awesomness</a>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target=".navbar-collapse" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="navbar-collapse collapse d-sm-inline-flex flex-sm-row-reverse">
<ul class="navbar-nav flex-grow-1">
<li class="nav-item">
<a class="nav-link text-dark">Top Sellers</a>
</li>
<li class="nav-item dropdown">
<a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
Products
</a>
<div class="dropdown-menu custom-dropdown border-0 border-bottom text-center" aria-labelledby="navbarDropdown">
<div class="row">
<div class="col-sm-3">
<label class="font-weight-bold">Item 1 </label>
<a class="dropdown-item" href="#">Top Sellers</a>
<a class="dropdown-item" href="#">Hot and New</a>
<a class="dropdown-item" href="#">Link 3</a>
</div>
<div class="col-sm-3">
<label>DVDs </label>
<a class="dropdown-item" href="#">Link 1</a>
<a class="dropdown-item" href="#">Link 2</a>
<a class="dropdown-item" href="#">Link 3</a>
</div>
<div class="col-sm-3">
<label>Books </label>
<a class="dropdown-item" href="#">Link 1</a>
<a class="dropdown-item" href="#">Link 2</a>
<a class="dropdown-item" href="#">Link 3</a>
</div>
<div class="col-sm-3">
<label>CDs </label>
<a class="dropdown-item" href="#">Link 1</a>
<a class="dropdown-item" href="#">Link 2</a>
<a class="dropdown-item" href="#">Link 3</a>
</div>
</div>
</div>
</li>
</ul>
</div>
</div>
</nav>
<div class="container-fluid mt-2 pt-5">
<div class="row" style="background-color: pink; height:800px;">
CONTENT
</div>
</div>