void BasePage_PreInit(object sender, EventArgs e)
        {
            var theme = ConfigHelper.DefaultTheme;
            if (!string.IsNullOrEmpty(this.SelectedTheme))
            {
                theme = this.SelectedTheme;
            }
            this.Theme = theme;
        }

public string SelectedTheme
        {
            set
            {
                HttpCookie cookie = new HttpCookie(CookieConstant.SelectedTheme);
                cookie.Value = value;
                Response.SetCookie(cookie);

                HttpCookie a;
                System.Net.Cookie b;
            }
            get
            {
                var cookie = Request.Cookies[CookieConstant.SelectedTheme];
                if (cookie == null || cookie.Value == null)
                    return null;
                else
                    return cookie.Value;
            }
        }