Program.cs

using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Threading.Tasks;

namespace ShopWebApp
{
    public class Program
    {
        public static void Main(string[] args)
        {
            CultureInfo.DefaultThreadCurrentCulture = new CultureInfo("pl-PL");
            CreateHostBuilder(args).ConfigureAppConfiguration((hostContext, builder) => { 
                if(hostContext.HostingEnvironment.IsDevelopment())
                {
                    builder.AddUserSecrets<Program>();
                }
            }).Build().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }
}