[Custom Environment variable in SwiftUI]

CustomEnvironmentVariable.swift

// 1. Create the key with a default value
private struct CaptionColorKey: EnvironmentKey {
  static let defaultValue = Color(.secondarySystemBackground)
}

// 2. Extend the environment with our property
extension EnvironmentValues {
  var captionBackgroundColor: Color {
    get { self[CaptionColorKey.self] }
    set { self[CaptionColorKey.self] = newValue }
  }
}

// 3. Optional convenience view modifier
extension View {
  func captionBackgroundColor(_ color: Color) -> some View {
    environment(\.captionBackgroundColor, color)
  }
}

// https://useyourloaf.com/blog/swiftui-custom-environment-values/