我正试图为我的学校项目构建一个基本的引导站点，它进行得很顺利，直到我想添加一个下拉菜单。因此，到目前为止，下拉列表的行为就像一个默认的导航链接，尽管我从官方的引导文档中看到了ctrl+c和ctrl+v-d。后来，我复制粘贴了整个示例导航，由于缺少更好的单词，它完全脱离了自己。
在反复阅读代码后，我放弃了，来到这里寻求您的帮助！
代码在这里：
.navbar{
margin:0;
padding-right: 10px;
width:100%;
overflow-x: hidden;
border-radius: 0;
}
footer{
position:absolute;
bottom:0;
width:100%;
}<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Recipeheaven</title>
<!--Bootstrap-->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/js/bootstrap.min.js"></script>
<!--JQuery-->
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<!--My own CSS-->
<link rel="stylesheet" href="css/master.css">
<!-- Javascript -->
<script src="js/main.js"></script>
</head>
<body>
<div id="container">
<header>
<nav class="navbar navbar-expand-sm bg-light navbar-light">
<ul class="nav navbar-nav">
<li class="nav-item"><a class="nav-link" href="#">Home</a></li>
<li class="nav-item"><a class="nav-link" href="#">Home</a></li>
<li class="nav-item"><a class="nav-link" href="#">Home</a></li>
<li class="nav-item"><a class="nav-link" href="#">Home</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">
Dropdown
</a>
<div class="dropdown-menu" aria-labelledby="navbarDropdown">
<a class="dropdown-item" href="#">Action</a>
<a class="dropdown-item" href="#">Another action</a>
<div class="dropdown-divider"></div>
<a class="dropdown-item" href="#">Something else here</a>
</div>
</li>
</ul>
<ul class="nav navbar-nav navbar-right">
<li class="nav-item"><a class="nav-link" href="#">Home</a></li>
</li>
</ul>
</nav>
</header>
<footer>
<footer class="bg-light text-center text-lg-start">
<div class="text-center p-3" style="background-color: rgba(0, 0, 0, 0.2)">
© 2020 Copyright:
<a class="text-dark" href="https://mdbootstrap.com/">MDBootstrap.com</a>
</div>
</footer>
</footer>
</div>
</body>
</html>删除二次关闭</li>标记，并将jQuery脚本标记移到引导脚本标记上方。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Recipeheaven</title>
<!--JQuery-->
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<!--Bootstrap-->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/js/bootstrap.min.js"></script>
<!--My own CSS-->
<link rel="stylesheet" href="css/master.css">
<!-- Javascript -->
<script src="js/main.js"></script>
</head>
<body>
<div id="container">
<header>
<nav class="navbar navbar-expand-sm bg-light navbar-light">
<ul class="nav navbar-nav">
<li class="nav-item"><a class="nav-link" href="#">Home</a></li>
<li class="nav-item"><a class="nav-link" href="#">Home</a></li>
<li class="nav-item"><a class="nav-link" href="#">Home</a></li>
<li class="nav-item"><a class="nav-link" href="#">Home</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">
Dropdown
</a>
<div class="dropdown-menu" aria-labelledby="navbarDropdown">
<a class="dropdown-item" href="#">Action</a>
<a class="dropdown-item" href="#">Another action</a>
<div class="dropdown-divider"></div>
<a class="dropdown-item" href="#">Something else here</a>
</div>
</li>
</ul>
<ul class="nav navbar-nav navbar-right">
<li class="nav-item"><a class="nav-link" href="#">Home</a></li>
</ul>
</nav>
</header>
<footer>
<footer class="bg-light text-center text-lg-start">
<div class="text-center p-3" style="background-color: rgba(0, 0, 0, 0.2)">
© 2020 Copyright:
<a class="text-dark" href="https://mdbootstrap.com/">MDBootstrap.com</a>
</div>
</footer>
</footer>
</div>
</body>
</html>
您使用的是链接下拉列表，而不是按钮下拉列表：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Recipeheaven</title>
<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.0-beta1/dist/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-giJF6kkoqNQ00vy+HMDP7azOuL0xtbfIcaT9wjKHr8RbDVddVHyTfAAsrekwKmP1" crossorigin="anonymous">
<!--My own CSS-->
<link rel="stylesheet" href="css/master.css">
</head>
<body>
<div>
<header>
<nav class="navbar navbar-expand-sm bg-light navbar-light">
<ul class="nav navbar-nav">
<li class="nav-item"><a class="nav-link" href="#">Home</a></li>
<li class="nav-item"><a class="nav-link" href="#">Home</a></li>
<li class="nav-item"><a class="nav-link" href="#">Home</a></li>
<li class="nav-item"><a class="nav-link" href="#">Home</a></li>
<li class="nav-item">
<div class="dropdown">
<button class="btn btn-secondary dropdown-toggle" type="button" id="dropdownMenuButton" data-bs-toggle="dropdown" aria-expanded="false">
Dropdown button
</button>
<ul class="dropdown-menu" aria-labelledby="dropdownMenuButton">
<li><a class="dropdown-item" href="#">Action</a></li>
<li><a class="dropdown-item" href="#">Another action</a></li>
<li><a class="dropdown-item" href="#">Something else here</a></li>
</ul>
</div>
</li>
</ul>
<ul class="nav navbar-nav navbar-right">
<li class="nav-item"><a class="nav-link" href="#">Home</a></li>
</li>
</ul>
</nav>
</header>
<footer>
<footer class="bg-light text-center text-lg-start">
<div class="text-center p-3" style="background-color: rgba(0, 0, 0, 0.2)">
© 2020 Copyright:
<a class="text-dark" href="https://mdbootstrap.com/">MDBootstrap.com</a>
</div>
</footer>
</footer>
</div>
</body>
<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.0-beta1/dist/js/bootstrap.bundle.min.js" integrity="sha384-ygbV9kiqUc6oa4msXn9868pTtWMgiQaeYH7/t7LECLbyPA2x65Kgf80OJFdroafW" crossorigin="anonymous"></script>
<!-- Javascript -->
<script src="js/main.js"></script>
</html>代码笔：https://codepen.io/manaskhandelwal1/pen/XWjxbmB?editors=1000