You know the minimise / restore / 'X' buttons at the top right of every window?

I only just noticed that the 'X' is no longer elongated; the buttons are all square. This is for desktop as well as UWP programs (previously I know UWP UI had distinctively square buttons)

Ever since Windows Classic (Windows 2000 look) was no longer available in Windows 8, I hoped for a way to bring back those 'window metrics' (which I think define that look more than any colour scheme) but I'd about given up.

And this morning it struck me! Well, it's close enough to the old look that I'm satisfied, albeit bemused how I could have overlooked it until now. Am I being slow? When did it change exactly...?