W3Schools Tryit Editor

<!DOCTYPE html>
<html lang="en">
<title>W3.CSS</title>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://www.w3schools.com/w3css/6/w3.css">
<body class="w3-container" style="padding-top:64px;padding-bottom:64px">

<h2>Reserve Space for Fixed Bars</h2>
<p>These bars stay at the top and bottom of the viewport while the page scrolls.</p>
<p>The body reserves space for both bars with 64px of top and bottom padding.</p>
<p>Remove the padding and run the example to see why the space is needed.</p>

<header class="w3-top w3-container w3-teal">
  <p>Fixed top bar</p>
</header>

<footer class="w3-bottom w3-container w3-teal">
  <p>Fixed bottom bar</p>
</footer>

<section class="w3-panel w3-light-grey" style="min-height:60vh">
  <h3>Beginning of the Page</h3>
  <p>Scroll down and watch the fixed bar.</p>
</section>

<section class="w3-panel w3-light-grey" style="min-height:60vh">
  <h3>Middle of the Page</h3>
  <p>The content moves while the bar stays in place.</p>
</section>

<section class="w3-panel w3-light-grey" style="min-height:60vh">
  <h3>End of the Page</h3>
  <p>Scroll back up to compare the positions.</p>
</section>

</body>
</html>