There's also an element for defining text as important: <strong></strong>.

<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.