public IServiceProvider ConfigureServices(IServiceCollection services)
{
    services.AddMvc().AddControllersAsServices();

    var container = new Container().WithDependencyInjectionAdapter(services);
    return container.ConfigureServiceProvider<CompositionRoot>();
}

var builder = new HostBuilder()
    .ConfigureAppConfiguration((hostingContext, config) => { ... })
    .ConfigureServices((hostContext, services) =>
    {
        services.AddOptions();
        // configure services
    })
    .ConfigureLogging((hostingContext, logging) => { ... });

var builder = new HostBuilder()
    .ConfigureAppConfiguration((hostingContext, config) => { ... })
    .ConfigureServices((hostContext, services) =>
    {
        services.AddOptions();
        // configure services
    })
    .ConfigureLogging((hostingContext, logging) => { ... })
    .UseStartup<Startup>(); //<-- That Startup class would have the `IServiceProvider ConfigureServices`