页面代码：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<link rel="stylesheet" href="red.css" id="lf"/></link>
</head>
<script>
function abc(obj)
{
var linkfile=document.getElementById('lf');
var c=obj.selectedIndex;
if(c==1) linkfile.href='red.css';
else if(c==2) linkfile.href='green.css';
else linkfile.href='yellow.css';
}
</script>
<body>
<div></div>
<select id="selCss" onchange="abc(this)">
<option value="0">请选择颜色</option>
<option value="1">红色</option>
<option value="2">绿色</option>
<option value="3">黄色</option>
</select>
</body>
</html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<link rel="stylesheet" href="red.css" id="lf"/></link>
</head>
<script>
function abc(obj)
{
var linkfile=document.getElementById('lf');
var c=obj.selectedIndex;
if(c==1) linkfile.href='red.css';
else if(c==2) linkfile.href='green.css';
else linkfile.href='yellow.css';
}
</script>
<body>
<div></div>
<select id="selCss" onchange="abc(this)">
<option value="0">请选择颜色</option>
<option value="1">红色</option>
<option value="2">绿色</option>
<option value="3">黄色</option>
</select>
</body>
</html>