I got it to work using the code below, now the banners resize when on mobile site.
COPY CODE
<center>
<style type="text/css">
.adslot_1 { width: 320px; height: 50px; }
@media (min-width:500px) { .adslot_1 { width: 468px; height: 60px; } }
@media (min-width:800px) { .adslot_1 { width: 728px; height: 90px; } }
</style>
<script async src="http://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script>
<ins class="adsbygoogle adslot_1" style="display:inline-block;" data-ad-client="ca-pub-123456" data-ad-slot="123456"></ins>
<script>(adsbygoogle = window.adsbygoogle || []).push({});</script>
</center>
Don’t forget to change the ca-pub and ad-slot.