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'
