import SwiftUI

struct SpringDemo: View {
  @State private var on = false
  var body: some View {
    VStack(spacing: 12) {
      Circle()
        .fill(on ? .green : .gray)
        .frame(width: on ? 120 : 60, height: on ? 120 : 60)
      Button("Toggle") {
        withAnimation(.spring(response: 0.4, dampingFraction: 0.6)) { on.toggle() }
      }
    }
    .padding()
  }
}

                    

import SwiftUI

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

                    

import SwiftUI

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