ASP.net core MVC catch all route serve static file

I had to make some additions to @DavidG answer. Here is what I ended up with

Startup.cs

app.UseStaticFiles();

app.UseMvc(routes =>
{
   routes.MapRoute("default", "{controller}/{action}");

   routes.MapRoute("Spa", "{*url}", defaults: new { controller = "Home", action = "Spa" });
});

HomeController.cs

public class HomeController : Controller
{
  public IActionResult Spa()
  {
      return File("~/index.html", "text/html");
  }
}