Creating fake dialogue boxes and windows is nothing new, that has been around forever. Maybe using css to determine the os/browser and mimic each one’s style is the new concept. I’ll believe it when someone can show me a webpage that proves it live.
The article does provide a test to distinguish authentic login pages from ones spoofed via CSS:<p>>Genuine OAuth or payment windows are in fact separate browser instances that are distinct from the primary page. That means a user can resize them and move them anywhere on the monitor, including outside the primary window.
Using an uncommon browser with non-default settings on an uncommon OS makes me a good target for finger-printing. Seems this kind of stuff is the upside now, where I would easily spot the differences (probably, would also like to interact with a working example).