How can I create a Shared project for iOS and Android?

I use Visual Studio for Mac and I want to have everything in one solution. The iOS and the Android project. Both projects should share the same code(Game1.cs and new classes that I will add) but I want to have two Content projects, one for iOS and one for Android, because I don’t know yet if I will use the same sprites on both platforms. Maybe it is necessary to use other sprites or sprites in a different resolution on one of the two platforms.

First, I created a Shared code project and after that I added the iOS and Android project to the solution. What should I do now? What are the next steps? How can I set up the projects so that I can use the shared code in both projects and one Content project for each platform?