override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        self.gradientLayer = CAGradientLayer()
        self.gradientLayer.frame = self.skeletonView.bounds
        self.gradientLayer.startPoint = CGPoint(x: 0.0, y: 1.0)
        self.gradientLayer.endPoint = CGPoint(x: 1.0, y: 1.0)
        self.gradientLayer.colors = [UIColor.green.cgColor, UIColor.blue.cgColor]
        self.skeletonView.layer.addSublayer(self.gradientLayer)
    }