To define strings as important, we use the <strong> and </strong> tags.

<html>
<body>
<h1>My favorite things</h1>
  <p>
  Raindrops on <em>roses</em><br>
  Whiskers on <strong>kittens</strong>
  </p>
</body>
</html>
]]>

Make sure you start with the opening tag and end with the closing tag.