private func layoutButton () {
        view.addSubview(doBoundWitnessButton)
        doBoundWitnessButton.translatesAutoresizingMaskIntoConstraints = false
        doBoundWitnessButton.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
        doBoundWitnessButton.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true