How to find div in findcontrol

protected void Page_Load(object sender, EventArgs e)
    {
Login Login1 = (Login)LoginView3.FindControl("Login1");
        HtmlGenericControl presledek = (HtmlGenericControl)Login1.FindControl("presledek");
        presledek.Style.Add("margin-top", "-8px");
}
 
Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about ...