adding CSS file dynamically

call this Feature on the button event

where font size will be increased or decresed  using upon the Style sheet

System.Web.UI.HtmlControls.HtmlLink link = new System.Web.UI.HtmlControls.HtmlLink();

        link.Href = "~Styles/Site.css";

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

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

        This.Controls.Add(link);