UIAlertController: аддсубвиев

Я хочу добавить подвид к моему контроллеру предупреждений. Но почему кнопки идут сверху? Как решить проблему?

    let alert = UIAlertController(title: nil, message: nil, preferredStyle: UIAlertControllerStyle.alert)

    let somethingAction = UIAlertAction(title: "Something", style: .default, handler: {(alert: UIAlertAction!) in print("something")})

    let cancelAction = UIAlertAction(title: "Annuler", style: .cancel, handler: {(alert: UIAlertAction!) in print("cancel")})

    alert.addAction(somethingAction)
    alert.addAction(cancelAction)

    let customView = UIView()
    customView.backgroundColor = .green
    customView.translatesAutoresizingMaskIntoConstraints = false
    customView.widthAnchor.constraint(equalToConstant: 128).isActive = true
    customView.heightAnchor.constraint(equalToConstant: 128).isActive = true

    alert.view.addSubview(customView)

    customView.centerXAnchor.constraint(equalTo: alert.view.centerXAnchor).isActive = true
    customView.topAnchor.constraint(equalTo: alert.view.topAnchor).isActive = true
    customView.bottomAnchor.constraint(equalTo: alert.view.bottomAnchor, constant: -32).isActive = true
    self.present(alert, animated: true, completion:{})