Basic Theme: Added Leaderboard Ad

Added the following code to header.php:

<div id="leaderboard"><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script>
<!-- SA-LeaderBoard -->
<ins class="adsbygoogle"
     style="display:inline-block;width:728px;height:90px"
     data-ad-client="ca-pub-1786161350237793"
     data-ad-slot="8804002359"></ins>
<script>
(adsbygoogle = window.adsbygoogle || []).push({});
</script>></div>

Then, added the following code to Custom CSS:

#leaderboard { width:728px; margin: 10px auto 0px auto; height: 90px; }