Css not being applied?

  echo '
<center>
<table class="tableBG">
<tr>
<th>Boy Names</th>
<th>Girls Names</th>
</tr>';

  $i = 0;
  while($i < $count) {
    echo '<tr>';
    if(isset($arr['BoysName'][$i])) { echo '<td>'.$arr['BoysName'][$i].'</td>'; }
    else{ echo '<td class="noBorder"> </td>'; }
    if(isset($arr['GirlsName'][$i])) { echo '<td>'.$arr['GirlsName'][$i].'</td>'; }
    else{ echo '<td class="noBorder"> </td>'; }
    echo '</tr>';
    $i++;
  }

.tableBG {
  border:0;
  width:400px;
}
.tableBG th, .tableBG td {
  border:1px solid gray;
}
.tableBG td.noBorder {
  border:0;
}