CSS file blocked: MIME type mismatch (X-Content-Type-Options: nosniff)

I am developing an Angular 4 app and I want to apply some global styles. Following the tutorial at the angular site, I've created a "styles.css" file in the root directory of my app, and I'm referring to that stylesheet in the index.html of my app:

<link rel="stylesheet" type="text/css" href="styles.css">


The angular app is successfully compiled:

$ ng serve
** NG Live Development Server is listening on localhost:4200, open your browser on http://localhost:4200 **
[...]
webpack: Compiled successfully.


But when I visit http://localhost:4200 in a Chromium browser, the console shows an error at

GET http://localhost:4200/styles.css


In a Firefox browser, the error is a bit more explicit:

GET
http://localhost:4200/styles.css [HTTP/1.1 404 Not Found 15ms]
The resource from "http://localhost:4200/styles.css" was blocked due to MIME type mismatch (X-Content-Type-Options: nosniff).


Both files, index.html and styles.css are located in the root directory of my angular app. I've tried to get more info about the problem :

nosniff
Blocks a request if the requested type is

"style" and the MIME type is not "text/css", or
"script" and the MIME type is not a JavaScript MIME type.


But I don't understand why it's bloking the request, since I've specified type="text/css" when referencing the stylesheet.

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