// Example：
// Change in viewDidLoad
override func viewDidLoad() {
    super.viewDidLoad()

    self.navBarBgAlpha = 0
    self.navBarTintColor = .white
}

// Change in scrollView scroll
func scrollViewDidScroll(_ scrollView: UIScrollView) {

    if scrollView.contentOffset.y > 100 {
        navBarBgAlpha = 1
        navBarTintColor = UIColor.defaultNavBarTintColor()
    } else {
        navBarBgAlpha = 0
        navBarTintColor = .white
    }

}