You can add external resources like CSS and JavaScript to your fiddle.
Add resource by:
URL from the web – this will embed the specific URL in your fiddle.
CDNJS – just start typing a library name and an autocompelete will suggest libraries you and insert:
If you want to use a dynamic resource please add a dummy GET variable i.e. http://example.com/dynamically.php?somevar=somevalue&dummy=.css. This will tell JSFiddle to recognize it as a CSS resource.