Mon premier site et ses imcompatibilité

/* Left sidebar and menu */
#leftside {
    margin:-30px 10px;
	padding:0;
	width: 150px;
	float:left;
	}
#leftside ul {
    list-style:none; 
	margin:0 0 18px; 
	padding:0; 
	width: 150px;
	}
#leftside ul li {
	/*position: relative;  (si on le met, ne marche pas avec IE7)*/
	padding:0;
	clear:both;
	}
	
#leftside ul li a {
    background: repeat-x bottom left #f4f4f4 ;
    border-bottom:1px solid #d8d8d8;
	border-right:1px solid #d8d8d8; 
	border-top:1px solid #d8d8d8;
	border-left:1px solid #d8d8d8;
	color:#505050; 
	font-size:1em;
	font-weight:700;  
	padding:5px 1px 5px 5px; 
	text-decoration:none; 
	width:138px;
	float:left;
	}
	
#leftside ul li.extend a {
    background: url(img/fleche.gif) right no-repeat  #f4f4f4 ;
	}


#leftside .announce {
    background: repeat-x bottom left #f4f4f4; 
	border-bottom:1px solid #d8d8d8; 
	border-left:4px solid #ccc; 
	border-right:1px solid #d8d8d8;
	border-top:1px solid #d8d8d8; 
	clear:left; color:#505050; 
	line-height:1.3em; 
	margin: 100px 0; 
	padding:5px 5px 5px; 
	width:134px;
	}
#leftside p,.announce p {font-size:0.9em;}
	
#leftside ul ul li a {
    margin-bottom:0px; 
	}

#leftside ul ul {
    position: absolute;
	font-size:0.9em; 
    margin:0 0 0 15px; 
	padding:0 0 5px 0; 
	width:150px;
	left: 266px; /*décalage des sous menus vers la droite*/
	display:none;
	}


#leftside ul.niveau1 li.sousmenu:hover ul.niveau2 , 
#leftside ul.niveau1 li.extend:hover ul.niveau2 {
    display:block;
    }
	 
#leftside ul li a:hover{
	background:repeat-x bottom left #C9C9C9;
	border-bottom:1px solid #b0b0b0;
	border-right:1px solid #b0b0b0;
	border-top:1px solid #b0b0b0;
	}	
	
#leftside ul li.extend a:hover {
    background: url(img/fleche.gif) right no-repeat #C9C9C9 ;
	}
	
#leftside ul li.extend:hover ul.niveau2 li a{
    background:  #f4f4f4;
	background-image: none ;
	}

#leftside ul li.extend:hover ul.niveau2 li a:hover{
    background: #C9C9C9;
	background-image: none ;
	}