/*navigation menu*/
div#nav {
float: left;
padding: 8px;
margin-top: 5px;
width: 99px;
  voice-family: "\"}\"";
 voice-family: inherit;
   width: 115px;
 }
div#nav ul {
margin: 0px;
padding: 0px;
background: white;
width: 115px;
}
div#nav li {
position: relative;
list-style: none;
margin: 0;
background: white;
padding: 0px;
border-bottom: 3px solid #FFF;
}
div#nav li:hover {
background: #B6C5D6;
}
div#nav li.submenu {
height:26px;
width: 118px;
font-size: 13px;
background:  url('images/bouton.gif') no-repeat 4px 0;
}
div#nav li.submenu:hover {
background:  url('images/bouton.gif') no-repeat 4px -26px;
}
div#nav li.subsubmenu {
width: 150px;
background-color: #FFF;
}
div#nav li.subsubmenu:hover {
background-color: #B6C5D6;
}
div#nav li.subsubsubmenu {
width: 150px;
background-color: #E7ECF1;
}
div#nav li.subsubsubmenu:hover {
background-color: #B6C5D6;
}

div#nav li a {
display: block;
padding: 0.25em 0 0.25em 0.5em;
text-decoration: none;
}
div#nav li a:hover {
display: block;
color : #FFF;
}
div#nav>ul a {
width: auto;
}
div#nav ul ul {
position: absolute;
top: 0;
left: 118px;
display: none;    
border: 1px dashed #79C;
}
div#nav ul ul ul{
position: absolute;
top: 0;
left: 150px;
display: none;
}
div#nav ul.level1 li.submenu:hover ul.level2,
div#nav ul.level2 li.submenu:hover ul.level3 {
display:block;
font-size: 11.5px;
 width: 150px;
 }
div#nav ul.level1 li.subsubsubmenu:hover ul.level2,
div#nav ul.level2 li.subsubmenu:hover ul.level3 {
display:block;
font-size: 11.5px;
 width: 150px;
 }

 <div id="nav">
<ul class="level1">
<li class="submenu"><a href="">Contact</a>
 <ul class="level2">
     <li><a href="/contact/equipe_enseignons.php">Equipe d'Enseignons</a></li>
     <li><a href="/contact/support_technique.php">Support Technique</a></li>
     <li><a href="/contact/relations_publiques.php">Relations Publiques</a></li>
       </ul>
 </li>
<li class="submenu"><a href="">Aide</a>
    <ul class="level2">
     <li><a href="/aide/comment-ca-fonctionne.php">Premiers pas</a></li>
       <li><a href="/aide/plan-du-site.php">Plan du site</a></li>
         <li><a href="/aide/questions-frequentes.php">Questions Fréquentes</a></li>
 <li><a href="/aide/aide-en-ligne.php">Aide en ligne</a></li>
       </ul>
 </li>
</ul>