How to define the HTML file extension in Visual Studio?

My project does not recognize the css and other files in the html files I have created, although I have written the extension paths correctly. How can I fix? enter image description here

enter image description here


First of all you need to configure serving static files in Startup

app.UseStaticFiles(); //serves wwwroot by default

To serve your theme folder you need to add the following lines

app.UseStaticFiles(new StaticFileOptions
    FileProvider = new PhysicalFileProvider(
        Path.Combine(Directory.GetCurrentDirectory(), "theme")),
    RequestPath = "/theme"