Just figured it out ...
echo "<table class='returnto'>\n";
echo "<tr>\n";
echo "<td><a target='_blank' href='http://sgs4.com'>Return to sgs4.com</a></td>";
echo "</tr>\n";
echo "</tr></table>\n";
/themes/default/default.css
.returnto {
font-family: Verdana, Arial, Helvetica;
color: #cccccc;
font-weight: bold;
font-size: 12px;
text-align: center;
width: 100%;
}
This adds a new class 'returnto'