import SwiftUI

struct ThemeDemo: View {
  @Environment(\.colorScheme) var scheme
  var body: some View {
    VStack(spacing: 12) {
      RoundedRectangle(cornerRadius: 8)
        .fill(.tint)
        .frame(height: 80)
        .overlay(Text("Tint").foregroundStyle(.white))
      Text(scheme == .dark ? "Scheme: Dark" : "Scheme: Light")
    }
    .padding()
  }
}

                    

import SwiftUI

struct ContentView: View {
  var body: some View { ThemeDemo() }
}

                    

import SwiftUI

@main
struct MyApp: App {
  var body: some Scene {
    WindowGroup { ContentView() }
  }
}