Refused to apply style from 'https://localhost:44314/App.styles.css' because its MIME type ('') is not a supported stylesheet MIME type, and strict MIME checking is enabled.

Refer here: https://learn.microsoft.com/th-th/aspnet/core/razor-pages/ui-class?view=aspnetcore-3.1&tabs=visual-studio#consume-content-from-a-referenced-rcl-1

When running the consuming app from build output (dotnet run), static web assets are enabled by default in the Development environment. To support assets in other environments when running from build output, call UseStaticWebAssets on the host builder in Program.cs:

using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Hosting;

public class Program
{
    public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }

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

Thanks for quick response. Works.

Wow! it's great helpful.