a11y-tests.css inspiration

[ffoodd]

@matuzo came up with the excellent a11y-tests.css, which basically simulate some accessibility situations — just like Atalan's french « L’accessibilité numérique, et si nous agissions ? » website does.

I think those ideas could be related to both ffoodd/a11y.css-webextension#15 and ffoodd/a11y.css#344 — and could reside in both main CSS file and webextension (as an independant level, I guess).