总结一下就是类似#gisarrow.over、#gisarrow.expanded这样的选择符
在使用javascript动态更改className的时候只有最先定义的一个样式有效
在IE6运行以下例子，然后删掉#gisarrow.over做个对比
IE7下还没试
IE6又一选择器bug？
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<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<style type="text/css">
#gisarrow {
width: 10px;
height:630px;
float: left;
background: #F3F3F3 url(http://124.42.44.70/ska/images/arrow-right.gif) no-repeat center;
}
#gisarrow.over {
background-color: #C3D9FF;
cursor: pointer;
}
#gisarrow.expanded {
background-image: url(http://124.42.44.70/ska/images/arrow-left.gif);
}
</style>
<script type="text/javascript">
function expand() {
var arrow = document.getElementById('gisarrow');
arrow.className = 'expanded';
}
function collapse() {
var arrow = document.getElementById('gisarrow');
arrow.className = '';
}
function arrowClick() {
var arrow = document.getElementById('gisarrow');
if (arrow.className == 'expanded') {
collapse();
} else {
expand();
}
}
</script>
</head>
<body>
<div id="gisarrow" onclick="arrowClick()"></div>
</body>
</html>