css are not loading

Guys I'm having the same problem.

My code in my view file.
<link rel="stylesheet" href="<?= base_url('bootstrap/css/bootstrap.min.css'); ?>" type="text/css">

The bootstrap assets are in a folder called bootstrap at the same level as the application folder.

/path/to/web/root/
├── application/
└── views/
├── templates
├── header.php
├── footer.php
├── system/
├── bootstrap/

rendered output
<link rel="stylesheet" href="http://localhost/codeigniter/bootstrap/css/bootstrap.min.css" type="text/css">

I've tried different locations within the project, nesting it in the application folder and under views but with the same non result even thought the path always seems to correct in relation to the local folder structure. Trying to access the css files directly through the browser generates a 404?

If I link to external css files they load fine.

What esoteric thing could be going on here? I've spent a nearly a day on this and its driving me insane.

I've got myself ready for a massive face palm.

TIA