CSS is served as Content-Type:text/html;

[marcus-at-localhost]

For some reason the css is served as Content-Type: text/html and thus there are no styles applied to the preview. Javascript is served fine though.

Request URL:http://127.0.0.1:51004/public/github.css
Request Method:GET
Status Code:200 OK
Remote Address:127.0.0.1:51004
Referrer Policy:no-referrer-when-downgrade

# Response Headers
HTTP/1.1 200 OK
Last-Modified: Mi, 13 Sep 2017 19:46:05 GMT
Content-Length: 16095
Accept-Ranges: bytes
Content-Type: text/html; charset=UTF-8
Date: Wed, 13 Sep 2017 20:35:54 GMT
Server: siebenmo

# Request Headers
GET /public/github.css HTTP/1.1
Host: 127.0.0.1:51004
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.79 Safari/537.36
Accept: text/css,*/*;q=0.1
DNT: 1
Referer: http://127.0.0.1:51004/view/36
Accept-Encoding: gzip, deflate, br
Accept-Language: de,en-US;q=0.8,en;q=0.6

Any idea? I already uninstalled/installed the extension and it happens in all browsers.

[marcus-at-localhost]

Holy freak, I found the solution, thanks to this comment: https://github.com/pallets/flask/issues/1045#issuecomment-42202749

The python mimetypes module pulls the values from the registry on windows so somehow your registry has got a bit messed up.

I ended up in bottle.py trying to understand where the wrong content/mime type is coming from and it's my windows registry!