iPhone X, iOS 11 - Tabbar Background

Hi Xamarin-Community,

I have some questions about iOS 11 on the iPhone X. Particularly about the Tabbar.

How can I change the Tabbar background image, text color, image position like in iOS 10?
It seems that the functions TabBar.BackgroundImage, UITabBarItem.ImageInsets or UITabBarItem.TitlePositionAdjustment has no effect (iOS; Custom TabbedRenderer).

Do anyone have an idea how to solve my problem?