[SwiftUI] iOS15の場合、デフォルトでは、tableviewとnavigation barが透過されてしまう
ので、それを防ぐ

@main
class AppDelegate: UIResponder, UIApplicationDelegate {

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        
        // TabViewの背景色の設定
        UITabBar.appearance().backgroundColor = UIColor.white
        
        // NavigationBarの背景色の設定
        let appearance = UINavigationBarAppearance()
        appearance.configureWithOpaqueBackground()
        appearance.backgroundColor = UIColor.white
        UINavigationBar.appearance().standardAppearance = appearance
        if #available(iOS 15.0, *) {
            UINavigationBar.appearance().scrollEdgeAppearance = appearance
        }
        return true
    }