That's probably in arcade.php. He using tables with border colors to create the lines. You'd have to edit that file directly after hunting for it somewhere in the file. The code would look something like this:
PHP Code:
<table border="0" width="500" height="1" align="center" bordercolor="000000" cellspacing="0" cellpadding="0">
<tbody><tr><td width="200">
<table border="0" width="200" height="1" align="center" bordercolor="000000" cellspacing="0" cellpadding="0" bgcolor="000000">
<tbody><tr><td></td></tr>
</tbody></table>
</td>
<td width="198">
<table border="0" width="192" height="1" align="center" bordercolor="000000" cellspacing="0" cellpadding="0">
<tbody><tr><td></td></tr>
</tbody></table>
</td>
<td width="200">
<table border="1" width="200" height="1" align="center" bordercolor="000000" cellspacing="0" cellpadding="0" bgcolor="000000">
<tbody><tr><td></td></tr>
</tbody></table>
</td></tr>
</tbody></table>