Markup: templates/output/06-components/social-media-icons/facebook.html
<div class="c-socialmedia-icon"><svg viewBox="0 0 36 36">
<path class="shape" fill="none" d="M1 1h34v34H1z"/>
<path class="icon" fill="currentcolor" d="M22.787 8.397a10.947 10.947 0 0 0-2.975-.4c-3.059 0-4.391 1.416-4.391 4.278v1.926h-2.209v2.751h2.21V28h3.456V16.952h3.314l.2-2.748h-3.514v-1.728c0-1.048.2-1.643 1.558-1.643a10.141 10.141 0 0 1 1.983.227z"/>
</svg>
</div>
Source:
assets/sass/06-components/_components.socialmedia-icons.scss, line 7