在后台引入外部CSS文件

    protected void Page_Load(object sender, EventArgs e)

         {

            if (!Page.IsPostBack)

             {

                 HtmlLink link = new HtmlLink();

                 link.Attributes.Add("type", "text/css");

                 link.Attributes.Add("rel", "stylesheet");

                 link.Attributes.Add("href", url);//url为css路径

                this.Page.Header.Controls.Add(link);

             }

         }