gistfile1.cs

public static void RegisterStyleSheets(this Page page, IEnumerable<string> appRelativePaths)
{
    if (page == null) throw new ArgumentNullException("page");
    if (page.Header == null) throw new ArgumentException("Page header is unavailable.", "page");

    var links = appRelativePaths
        .Select(page.ResolveClientUrl)
        .Select(p =>
        {
            var link = new HtmlLink { Href = p };
            link.Attributes.Add("rel", "stylesheet");
            link.Attributes.Add("type", "text/stylesheet");
            return link;
        });

    foreach(var link in links)
        page.Header.Controls.Add(links);
}