I set up a secure version of my CSS server which points to a different folder which contains a version of the stylesheet with secure images in it, the robots.txt and .htaccess files are exactly the same (the only other files in the directory). The non-secure CSS file loads fine in the normal non-secure website, however it will not load in the secure version of the website.
When I inspect the element in Firebug, it shows this error:
Failed to load source for: https://css.animuson.com/fresh/style.css
and the CSS inspector says (like expected):
There are no rules in this stylesheet.
Edit: The CSS forbids access from external sources. You can access it without getting the 403 error by clicking the link from Firebug. Clicking it from here at Stack Overflow will throw the 403. You can also copy and paste the URL into the address bar.
However if I open that URL in my browser, it loads up the stylesheet just fine. I've tried adding a timestamp to the end of it in a query string to reload it, nothing seems to be working.