Csss

#block-system-main-menu .menu,
#block-system-main-menu .menu li {
  margin: 0;
 padding: 0;
 list-style: none;
}
  #block-system-main-menu .menu li {
    display: block;
    overflow: hidden;
    clear: both;
  }
#block-system-main-menu .menu li a {
      display: block;
      float: left;
      width: 100px;
      padding: 20px 0;
      background: url(../images/home.png) ;
      margin: 2px;
      text-align: center;
      color: #fff;
      text-decoration: none;
    }


 #block-system-main-menu .menu li.class a {
 background: url(../images/aboutus.png) ;
 background: url(../images/products.png) ;
 background: url(../images/contactus.png) ;
 }