On this Gmail app, my buttons have extra bottom padding for some reason which ruins the vertical alignment of the text.

This is the code I'm using:

<!--[if mso]>
<v:roundrect xmlns:v="urn:schemas-microsoft-com:vml" xmlns:w="urn:schemas-microsoft-com:office:word" href="http://www.google.com" style="height:60px;v-text-anchor:middle;width:284px;" arcsize="50%" stroke="f" fillcolor="#000000">
<w:anchorlock/>
<![endif]-->
<center>
<a class="btn" href="http://www.google.com" style="background-color: #000000; border-radius: 30px; color: #ffffff; display: inline-block; font-size: 21px; font-weight: 700; height: 60px; line-height: 60px; margin: 0 auto; text-decoration: none; width: 284px;">Call to Action</a>
</center>
<!--[if mso]>
/v:roundrect
<![endif]-->

Any ideas why this could be happening? Looks fine on other Gmail clients except for this specific one on the Nexus 6 running Marshmallow.