求助，怎样解决列表样式在IE6上面显示不了！！

.tySmClass{ width:220px; font-size:14px; margin-left:auto; margin-right:auto;}
.tySmClass img{margin-left:20px; margin-right:20px;}
.tySmClass span{width:220px; height:34px; line-height:34px; border-bottom:1px #a4a4a4 dotted; display:block; list-style:none;}
.tySmClass span a{color:#000;font-weight:bold; text-decoration:none; width:220px; height:34px; display:block;}
.tySmClass span a:hover{color:#000; text-decoration:none; font-weight:bold; background:url(../images/newslist_15.jpg) no-repeat center; width:220px; height:34px;}
.tySmClass span .onclck2{color:#000; text-decoration:none; font-weight:bold; background:url(../images/newslist_15.jpg) no-repeat center; width:220px; height:34px;}
.tySmClass ul{ width:220px;}
.tySmClass ul li{width:160px; height:25px; line-height:25px; margin-left:60px; }
.tySmClass ul li a{color:#333; text-decoration:none;font-size:12px;}
.tySmClass ul li a:hover{color:#333; text-decoration:none; font-weight:bold;}
.tySmClass ul li .onclck1{color:#333; text-decoration:none; font-weight:bold;}