Update: The Pixel Perfect checkbox makes a noticeable difference in appearance. I presume this is because older systems were developed before the advent of anti-aliasing, and were designed pixel by pixel.
No wonder OSX felt like the future.
I miss the future.
I'd say the same for the scrollbars, but these days I'd settle for reverting to them being visible at all times.
And if you really wanted to, maybe made some concessions, and were clever about it, you could maybe find a way so that users define shapes and functionality and a default light/dark color scheme, but applications could still use the "user style" with their own color scheme, and allow the user to switch between that and the user defined colors.
It would also have the side effect of ejecting the people who just change things to make their mark. There is no more mark to make! Except making the "style configurator" for the user better, collaborating on expanding the protocol shared between it and websites/applications. You can invent a new type of button, put it on the pile, and hope it becomes one of the higher rated ones that gets downloaded and used a lot, on any OS, in any application or website. That will be a lot less interesting for hack frauds, and software interfaces can finally become awesome and then just better from there.
https://getbootstrap.com/1.0.0/
They may have peaked with 2.0:
I agree that most of the other ones don’t look very button like to me either. But even so I would probably understand that most of them were buttons when I saw them in context on a page.
The flat style has been around for a while now, so I’ve gotten used to it even though when I started using computers it was on Windows 95 with the grey rectangular buttons with shaded sides that give them the “3d effect”.
And even flat style buttons often have changes when you hover and click, but it seems that they didn’t copy that part on this button collection page.
Introducing Mac OS X's Aqua interface, Steve Jobs said at Macworld in January 2000: "We made the buttons on the screen look so good you'll want to lick them."