代码示例:(标识:bs_navbar_fixed_bottom)
<!DOCTYPE html>
<html lang="en">
<head>
  <title>Bootstrap 实例</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link href="https://cdn.bootcdn.net/ajax/libs/twitter-bootstrap/5.1.2/css/bootstrap.min.css" rel="stylesheet">
  <script src="https://cdn.bootcdn.net/ajax/libs/twitter-bootstrap/5.1.2/js/bootstrap.bundle.js"></script>
</head>
<body style="height:1500px">

<nav class="navbar navbar-expand-sm bg-dark navbar-dark fixed-bottom">
  <div class="container-fluid">
    <a class="navbar-brand" href="#">固定在底部</a>
  </div>
</nav>

<div class="container-fluid"><br>
  <h3>固定在底部的导航栏</h3>
  <p>固定导航栏在独立于页面滚动的固定位置(顶部或底部)保持可见。</p>
  <h1>请滚动此页面来查看效果</h1>
</div>

</body>
</html>
运行结果: