javascript动态添加css类到style标签中

 <title>javascript动态给style标签添加css样式类示例代码</title>
 <style type="text/css" id='contentCss'></style>
<script language="JavaScript">
    var style = document.getElementById('contentCss'), css = 'p{ color:red; }p.p2{color:blue}p.p3{color:green}';
    if (style.styleSheet) style.styleSheet.cssText += css;
    else style.innerHTML += css;
 </script>
 <p>p1</p>
 <p class="p2">p2</p>
 <p class="p3">p3</p>