<link href="001.css" id="cssfile" rel="stylesheet" type="text/css" />
<script>
function changeStyle(name){
//alert(name);
var css = document.getElementById("cssfile");
css.href = name+".css";
}
</script>

<select onchange="changeStyle(this.options[this.selectedIndex].value)">
<option value="001" selected="selected">默认样式</option>
<option value="blue">蓝色经典</option>
<option value="red">红色梦幻</option>
</select>
<div id="cssTest">
我是一只小小小小小鸟！
</div>