当系统主题改变时，如何改变UIToolBar的颜色？

NotificationCenter.default.addObserver(self, selector: #selector(themeChanged), name: UIAccessibility.darkerSystemColorsStatusDidChangeNotification, object: nil)

@objc func themeChanged() {
    if #available(iOS 13.0, *) {
        let isDarkMode = UITraitCollection.current.userInterfaceStyle == .dark
        let toolbarColor = isDarkMode ? UIColor.black : UIColor.white
        UIToolbar.appearance().barTintColor = toolbarColor
    }
}