动态为页面添加CSS样式文件引用

动态为页面添加CSS样式文件引用：

 if (document.createStyleSheet) { //IE

     document.createStyleSheet("./Themes/Default/MessageTip.css");

 }

 else { //Firefox, Chrome

     var stylesheet = document.createElement("link");

     stylesheet.href = "./Themes/Default/MessageTip.css";

     stylesheet.rel = "stylesheet";

     stylesheet.type = "text/css";

     document.getElementsByTagName("head")[0].appendChild(stylesheet);

 }