Stylesheet not loaded because of MIME-type
The referenced path is wrong, the target path does not have a corresponding css file. Because the server returns a 404 error, it is in html format and does not match the css
In most cases, this could be simply the CSS file path is wrong. So the web server returns status: 404 with some Not Found content payload of html type.
The browser follows this (wrong) path from <link rel="stylesheet" ...> tag with the intention of applying CSS styles. But the returned content type contradicts so that it logs an error.