func applicationWillResignActive(_ application: UIApplication) {
    window?.addSubview(inactiveView)
    window?.bringSubview(toFront: inactiveView)
}

func applicationDidEnterBackground(_ application: UIApplication) {
    window?.addSubview(backgroundView)
    window?.bringSubview(toFront: backgroundView)
}

func applicationWillEnterForeground(_ application: UIApplication) {
    backgroundView.removeFromSuperview()
}

func applicationDidBecomeActive(_ application: UIApplication) {
    inactiveView.removeFromSuperview()
}