如何将按钮/视图放在SwiftUI地图的顶部？

import SwiftUI
import MapKit

struct ContentView: View {
    var body: some View {
        ZStack(alignment: .top) {
            MapView()
            Button(action: {
                // 按钮点击事件
                print("按钮被点击了")
            }) {
                Text("按钮")
                    .padding()
                    .background(Color.blue)
                    .foregroundColor(.white)
                    .cornerRadius(10)
            }
            .padding()
        }
    }
}

struct MapView: UIViewRepresentable {
    func makeUIView(context: Context) -> MKMapView {
        MKMapView(frame: .zero)
    }
    
    func updateUIView(_ uiView: MKMapView, context: Context) {
        let coordinate = CLLocationCoordinate2D(latitude: 37.7749, longitude: -122.4194)
        let span = MKCoordinateSpan(latitudeDelta: 0.2, longitudeDelta: 0.2)
        let region = MKCoordinateRegion(center: coordinate, span: span)
        uiView.setRegion(region, animated: true)
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}