As I recall it's in head.php and looks like this:
<tr>
<td align="center" valign="center">
<table width="95%" height="95%" bgcolor="#000000">
<tr>
<td>
<table width="100%" height="100%" align="center" bgcolor="#FFFFFF" cellpadding="10">
<tr>
Note: it's actually a cell of one color within a black cell (so it only looks like a border).