thanks for your post,
Did you get this to work ?
=> My issue is still active,
Have you checked the console to see what errors you are getting ?
=> No, but I don't see where I should find error log about this ? Where do you think, I should watch ?
Have you tried with a local css file instead ?
=> No, where do you think I should put my Css file ?
No worries, I know how hard extensions are to work with! if you need any sort of tutorial then I did a set on here and also on my blog http://qlikanddirty.com/category/extensions/extension-tutorial-series/
However, the console is very much your friend when trying to debug extensions! this is normally just accessed by hitting F12 in the browser. Chrome's tools are probably the best I think.
You can also use firebug in the actual qlikview application (see the tutorial) but it is limited what you can do.
The extension itself should just have a CSS file with it which you can alter.
If you want to share it, I would be more than happy to debug it for you
Thanks Adam, within the console I saw clearly the problem,
I used https for QlikView, but http for Google font (so security disabled the http part), I've just added an s and it's working
Thanks for your help