Bonjour,
Voila ce que m'affiche ma page css :
http://laisir.free.fr/voici2.png
Et voila ce qu'elle devré affiché(petit montage) :
http://laisir.free.fr/voici.png

et voila mon CSS :

body
{
 
  width: 760px;
   margin: auto;
   margin-top: 20px;
   margin-bottom: 20px;    
   background-image: url("fond4.png");
}


.entt
{
 -moz-border-radius : 5px 10px; 
   -moz-border-bottom-colors: #555 #666 #777 #888 #999 #aaa #bbb #ccc #bbb #aaa #999 #888 #777 #666 #555 ;  
   -moz-border-top-colors:    #555 #666 #777 #888 #999 #aaa #bbb #ccc #bbb #aaa #999 #888 #777 #666 #555 ;   
   -moz-border-left-colors:   #555 #666 #777 #888 #999 #aaa #bbb #ccc #bbb #aaa #999 #888 #777 #666 #555 ;   
   -moz-border-right-colors:  #555 #666 #777 #888 #999 #aaa #bbb #ccc #bbb #aaa #999 #888 #777 #666 #555 ;  
   width: 760px;
   height: 100px;
   background-image: url("motif2.png");
   background-repeat: no-repeat;
   margin-bottom: 10px;
   border: 10px solid black;
}


.menu
{
 -moz-border-radius : 5px 10px; 
   -moz-border-bottom-colors: #555 #666 #777 #888 #999 #aaa #bbb #ccc #bbb #aaa #999 #888 #777 #666 #555 ;  
   -moz-border-top-colors:    #555 #666 #777 #888 #999 #aaa #bbb #ccc #bbb #aaa #999 #888 #777 #666 #555 ;   
   -moz-border-left-colors:   #555 #666 #777 #888 #999 #aaa #bbb #ccc #bbb #aaa #999 #888 #777 #666 #555 ;   
   -moz-border-right-colors:  #555 #666 #777 #888 #999 #aaa #bbb #ccc #bbb #aaa #999 #888 #777 #666 #555 ;  
margin-top: 120px;
   float: left; 
   width: 120px; 
   background-color: #626262;
   background-image: url("motif.png");
   background-repeat: repeat-x;
   border: 10px solid black;
   margin-bottom: 20px; 
}

.contenu
{
 -moz-border-radius : 5px 10px; 
   -moz-border-bottom-colors: #555 #666 #777 #888 #999 #aaa #bbb #ccc #bbb #aaa #999 #888 #777 #666 #555 ;  
   -moz-border-top-colors:    #555 #666 #777 #888 #999 #aaa #bbb #ccc #bbb #aaa #999 #888 #777 #666 #555 ;   
   -moz-border-left-colors:   #555 #666 #777 #888 #999 #aaa #bbb #ccc #bbb #aaa #999 #888 #777 #666 #555 ;   
   -moz-border-right-colors:  #555 #666 #777 #888 #999 #aaa #bbb #ccc #bbb #aaa #999 #888 #777 #666 #555 ;  
   margin-left: 140px;
  width: 590px;
   padding: 5px;
   
   color: #B3B3B3;
   background-color: #626262;
   background-image: url("motif.png");
   background-repeat: repeat-x;
   border: 10px solid black;
}

Configuration: Windows Vista
Firefox