How can a named route have URL parameters in flutter web?

I'm building a web-app which needs to have a route that gets a post ID and then it will fetch the post using the ID.

How can I have URL arguments let's say /post/:id so id is the argument

My app looks like that currently:

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      // title: "Paste",
      initialRoute: "/",
      theme: ThemeData(
          primarySwatch: Colors.green,
          primaryColor: Colors.blue
      ),
      routes: {
        "/": (context) => HomePage(),
        "/post": (context) => PastieRoute()
      },
      debugShowCheckedModeBanner: false
    );
  }
}