import SwiftUI

struct CardStyle: ViewModifier {
  func body(content: Content) -> some View {
    content
      .padding()
      .background(.blue.opacity(0.1))
      .cornerRadius(8)
  }
}

extension View {
  func card() -> some View { modifier(CardStyle()) }
}

struct CustomModifiersDemo: View {
  var body: some View { Text("Hello").card() }
}

                    

import SwiftUI

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

                    

import SwiftUI

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