So I was following a tutorial on MVC, the tutor changed the default bootstrap theme into a bootstrap 4 lumen theme from bootswatch. I did the same but the theme, button, and navbars didnt show as it was in the tutorial. If I put a boostrap 3 theme, it goes a little fine (not the same as the preview the bootswatch site shows but it is better than what happens in bootstrap 4 or higher).
So I tried to fix this by upgrading the bootsrap from nuget into bootstrap 4, still the same. then I tried upgrading to bootstrap 5.1, the same result.
So what's wrong with this?
here is a screen shot of what happen if I use the bootswatch's bootsrap 5 (left) vs the bootstrap 3 version

here is my bundleconfig (there was an error in the 'bundles.Add(new ScriptBundle("~/bundles/bootstrap").Include(' and another tutorial told that to fix this, I should rewrite 'new ScriptBundle' into 'new Bundle')
public class BundleConfig
{
// For more information on bundling, visit https://go.microsoft.com/fwlink/?LinkId=301862
public static void RegisterBundles(BundleCollection bundles)
{
bundles.Add(new ScriptBundle("~/bundles/jquery").Include(
"~/Scripts/jquery-{version}.js"));
bundles.Add(new ScriptBundle("~/bundles/jqueryval").Include(
"~/Scripts/jquery.validate*"));
// Use the development version of Modernizr to develop with and learn from. Then, when you're
// ready for production, use the build tool at https://modernizr.com to pick only the tests you need.
bundles.Add(new ScriptBundle("~/bundles/modernizr").Include(
"~/Scripts/modernizr-*"));
//bundles.Add(new ScriptBundle("~/bundles/bootstrap").Include(
// "~/Scripts/bootstrap.js"));
bundles.Add(new Bundle("~/bundles/bootstrap").Include(
"~/Scripts/bootstrap.js"));
bundles.Add(new StyleBundle("~/Content/css").Include(
"~/Content/slate-4-bootstrap.min.css",
"~/Content/site.css"));
}
}