how to fix navbar at top in bootstrap 4 code example

Example 1: navbar fixed top bootstrap 5

<!-- on Bootstrap v5.0 simply add fixed-top class to nav.navbar -->

<nav class="navbar fixed-top navbar-light bg-light">
  <div class="container-fluid">
    <a class="navbar-brand" href="#">Fixed top</a>
  </div>
</nav>

Example 2: bootstrap navbar fixed top

<section id="headnev" class="navbar navbar-fixed-top">

Example 3: how to fix navbar in bootstrap

<nav className="fixed-top">