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">

<h2>Fixed Top Bar</h2>
<p>The <b>w3-top</b> class fixes an element at the top of the browser viewport.</p>
<p>The bar fills the viewport width and stays visible as you scroll.</p>
<p>The body has top padding to reserve space for the fixed bar.</p>

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

<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 page 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 position of the bar.</p>
</section>

</body>
</html>