protected void Page_Preinit(object sender,EventArgs e) 
    {
        HttpCookie theme = Request.Cookies["Theme"];
        if (theme == null)
        {
            this.Theme = "blue";
        }
        else
        {
            this.Theme = theme.Value;
        }
  
    }
    protected void Page_Load(object sender, EventArgs e)
    {
        if(!IsCallback)
        {
            HttpCookie theme = Request.Cookies["Theme"];
            if (theme != null)
            {
                string themestring = theme.Value;
                for (int i = 0; i < this.DropDownList1.Items.Count; i++)
                {
                    if (this.DropDownList1.Items[i].Value == themestring)
                    {
                        this.DropDownList1.SelectedIndex = i;
                    }
                }
            }
        }
    }
    protected void DropDownList1_SelectedIndexChanged1(object sender, EventArgs e)
    {
        Response.Cookies["Theme"].Value = this.DropDownList1.SelectedValue;
        Response.Redirect("login.aspx");
    }