This this I don't know if it will work but its worth a try, just save ur template
content before you do it so you can always revert back.
Code:
<!-- test -->
<style type="text/css">
<!--
.style5 {
font-size: 18px;
font-family: Arial, Helvetica, sans-serif;
}
-->
</style>
<tr>
<td align="center" width="100%"><div align="center"><span class="bigusername style5" color="#FFFFFF">$thread[title]</span>
</div></td></tr>
<div align="center"><br>
</div>
<!-- /test -->