html_email_button.html

<table cellspacing="0" cellpadding="0">
  <tr>
    <td align="center" width="300" height="40" bgcolor="#a10000" style="-webkit-border-radius: 5px; -moz-border-radius: 5px; border-radius: 5px; color: #fff; font-weight: bold; font-family: Helvetica, Arial, sans-serif; display: block;">
      <a href="http://www.EXAMPLE.com/" style="color: #fff; text-decoration: none; line-height:40px; width:100%; display:inline-block">
        Button Text Goes Here
      </a>
    </td>
  </tr>
</table>