struct DetailView: View {
   var body: some View {
      VStack {
         Text("Details")
      }
      .toolbar {
         ToolbarItem(placement: .automatic) {
            Button(action: {
               print("Adding Book")
            }, label: {
               Image(systemName: "plus")
            })
            #if os(macOS)
            .help("Press this button to add a book")
            .pointerStyle(.link)
            #endif
         }
      }
      .navigationTitle("My Title")
   }
}