At least for XFCE4, you could install some extra window variants. It took me a really long time to figure out it was this file installing the custom Appearance items for windows:
Some of the variations mimic other operating systems. It's nice. Do 'sudo pacman -Ss ' and a keyword of what you're looking for (such as 'xfwm' without the quotes) and you'll get an explanation if it's found. Good luck. Personally, I prefer the square ones, but hate the "flat" themes.
Code:
$ sudo pacman -Ss xfwm
...:
extra/xfwm4 4.18.0-2 (xfce4)
Xfce's window manager
extra/xfwm4-themes 4.10.0-5 (xfce4)
A set of additional themes for the Xfce window manager
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