You cannot make this Xamarin platform just using C #
Xamarin website form:
If you're a Java developer, you're well on the way to your skills and existing code on the Xamarin platform while reaping the benefits of reusing C # code. You will find that C # syntax is very similar to Java syntax, and that both languages are very similar functions. In addition, you will discover unique features for C # that will make your life easier.
https://developer.xamarin.com/guides/android/advanced_topics/xamarin-for-java/