ajouter un niveau menu CSS

<ul class="navigation">
  <li class="toggleSubMenu"><span>PORTABLES</span>
    <ul class="subMenu">
      <li><a href="/html/produitsalavente.php?rubrique=lap&sr=13p" class="LinkSubMenu">Portables 13"</a></li>
      <li><a href="/html/produitsalavente.php?rubrique=lap&sr=14p" class="LinkSubMenu">Portables 14"</a></li>
      <li><a href="/html/produitsalavente.php?rubrique=lap&sr=15p" class="LinkSubMenu">Portables 15"</a></li>
      <li><a href="/html/produitsalavente.php?rubrique=lap&sr=16p" class="LinkSubMenu">Portables 16"</a></li>
      <li><a href="/html/produitsalavente.php?rubrique=lap&sr=17p" class="LinkSubMenu">Portables 17"</a></li>
                                            <!--<div class="LinkSubMenu">T&eacute;moignage du Dr Fran&ccedil;ois Curnier - P.D.G. Digisens SA</div>-->
    </ul>
  </li>
  <li class="toggleSubMenu"><span>STATIONS</span>
    <ul class="subMenu">
      <li><a href="/html/produitsalavente.php?rubrique=bur" class="LinkSubMenu">Bureautique</a></li>
      <li><a href="/html/produitsalavente.php?rubrique=cre" class="LinkSubMenu">Cr&eacute;ation</a></li>
      <li><a href="/html/produitsalavente.php?rubrique=des" class="LinkSubMenu">Design</a></li>
      <li><a href="/html/produitsalavente.php?rubrique=mul" class="LinkSubMenu">Multimedia</a></li>
      <li><a href="/html/produitsalavente.php?rubrique=gam" class="LinkSubMenu">Gaming</a></li>
    </ul>
  </li>
</ul>

.navigation
{
  margin: 0;
  padding: 0;
  list-style: none;
  background:#ffffff;
  color: #eeeeee;
  width: 191px;
  font: 13px Arial, sans-serif;
}

.navigation a, .navigation span
{
  display: block;
  padding: 5px 0px 0px 10px;
  color: #eeeeee;
  text-decoration: none;
  background: transparent left bottom no-repeat;
  height:20px;
  border-bottom: 1px solid #666;
}

.navigation .toggleSubMenu a, .navigation .toggleSubMenu span
{
  background-image: url(menu-item-deroule-products.png);
}

.navigation .open a, .navigation .open span
{
  background-image: url(menu-item-enroule-products.png);
  font-weight:normal;
}

.navigation a:hover, .navigation a:focus, .navigation a:active
{
  text-decoration: none;
  font-weight:bolder;
}

.navigation .subMenu
{
  background: transparent url(subMenu.png) 0 0 repeat-x;
  font-size: 14px;
  margin: 0;
  padding: 0;
  border-bottom: 1px solid #666;
  list-style: none;
}

.navigation ul.subMenu a
{
  background: none;
  padding: 3px 20px;
}

a.LinkSubMenu
{
  font-size: 12px;
  font-weight:normal;
  text-decoration:none;
  color:#000000;
}

div.LinkSubMenu
{
  font-size: 12px;
}