class LightDarkVC: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let stack = UIStackView()
        stack.axis = .vertical
        stack.spacing = 20

        stack.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(stack)

        let g = view.safeAreaLayoutGuide
        NSLayoutConstraint.activate([
            stack.topAnchor.constraint(equalTo: g.topAnchor, constant: 40.0),
            stack.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 40.0),
            stack.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -40.0),
        ])

        let font: UIFont = .systemFont(ofSize: 24.0, weight: .bold)
        var v: UILabel!

        v = UILabel()
        v.text = "Default"
        v.textAlignment = .center
        v.font = font
        stack.addArrangedSubview(v)

        v = UILabel()
        v.text = "Always Light"
        v.textAlignment = .center
        v.overrideUserInterfaceStyle = .light
        v.font = font
        stack.addArrangedSubview(v)

        v = UILabel()
        v.text = "Always Dark"
        v.textAlignment = .center
        v.overrideUserInterfaceStyle = .dark
        v.font = font
        stack.addArrangedSubview(v)

        v = UILabel()
        v.text = "Explicit Colors\nWhite Background\nBlack .textColor"
        v.textAlignment = .center
        v.numberOfLines = 0
        v.backgroundColor = .white
        v.textColor = .black
        v.font = font
        stack.addArrangedSubview(v)

    }

}