plugins/sys/templates/user/preview/main.stpl
<table width="100%" height="100%">
<tr>
<td valign="center" align="center">
{if("template" eq "")}<span style="color:red;">-- {t(Empty)} --</span>{/if}
{template}
<br /><a href="javascript:void(0)" onclick="window.close()">{t(Close)}</a>
</td>
</tr>
</table>