Do you know of an icon set conversion of those that would work with gtk3? Even most icon themes that work with gtk2 are incorrectly structured for gtk3, with wrong icons display for, say, +/- controls. Using the ugly Adwaita set because it's the only complete and working one. The Haiku icon set also only works with gtk2.
no wonder, as MacOSX/OSX/macOS is the direct successor of NEXTSTEP (the OS), when Steve Jobs came back he managed that Apple buy his company. From Interfacebuilder (nowadays XCode) to Mail, several things in early MacOS X 1.0 server looked similar to the previous NEXTSTEP version (decorated with a MacOS 8/9 theme). http://toastytech.com/guis/osxsv.html
Compare yourself, see the "Apple MacOS "X section:
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Anyone notice some visual parallels between the icon aesthetic since El Capitan and Keith Ohlfs's icons?
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This guy recreated the NeXT icons (with some creative liberties):
http://galgot.free.fr/wordpress/?p=1380
http://galgot.free.fr/wordpress/?p=1410