js Dom className(ie6下的诡异)

<ul class="doc">
<li class="btn-wrap">
        <button type="submit" class="sbm">
        <span id="look"></span>查看适合的保险</button>
</li>
</ul>

.sbm span{left:0px;top:0px;position:absolute;width:100%;background:url(http://img01.taobaocdn.com/tps/i1/T10a0VXdREXXXXXXXX-112-44.png) left top no-repeat;}
.sbm:hover span{background-position:0 -24px}

<script>
YUI().use('node', function(Y){
        if(Y.UA.ie === 6){
                Y.one('.sbm span').on('mouseover',function(e){
                        //e.target.addClass('shover');
                        document.getElementById('look').className = 'sss';
                })
                Y.one('.sbm span').on('mouseout',function(e){
                        e.target.removeClass('shover');
                });
        }
})
</script>