This is a pretty old question, but since this is the best result on Google, I will put my solution here.
I had the same problem, my CSS files were accessible and loaded by the browser, but in fact they were not used. I could just browse CSS manually, but both Firefox and Chrome did not apply them.
This was my link tag:
<link href="/static/css/bootstrap.css" rel="stylesheet" type="text/css">
It looks good that the right way ... I even remembered to set the type, but not the cube.
As it turns out, my web server forced the content type in application/octet-stream CSS files. Therefore, even if I specified type in the link tag, Firefox and Chrome see the wrong type of content from the server and refuse to use stylesheets.
If you use Firefox with Firebug , you can see the type of content that your server sends on the Network tab.
In my case, using Lighttpd, the fix was to add ".css" => "text/css" to mimetypes.assign like this:
mimetype.assign = ( ".html" => "text/html", ".txt" => "text/plain", ".jpg" => "image/jpeg", ".png" => "image/png", ".css" => "text/css", "" => "application/octet-stream" )
Hope this saves someone from a couple of googling watches and heads scratching.
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