Use tag <h1>, <h2>, (...),<h4> for semantic headers.
Also it is possible to use an extra class .Heading--mega to change the level appearance.
<h1>Heading level 1</h1>
<h2>Heading level 2</h2>
<h3>Heading level 3</h3>
<h4>Heading level 4</h4>
<h1 class="Heading--mega">Heading mega</h1>