public class Program
{

  public static async Task Main(string[] args)

  {
      var environment = arguments["-env"]?.ToLower() ?? "development";

      var configBuilder = new ConfigurationBuilder()            
        .SetBasePath(baseDir)
        .AddJsonFile("appsettings.json", true, true)            
        .AddJsonFile($"appsettings.{environment.ToLower()}.json", optional: true, reloadOnChange: true)
        .AddEnvironmentVariables();
      ......
  }
  public static void Configure(HostBuilderContext hostContext, IServiceCollection services)
  {
    var cnString = configuration.GetConnectionString("DbConnectionString");
    services.AddDbContext<DbContext, ApplicationDbContext>(x => x.UseSqlServer(cnString));
    ...
  }
}