How to remove rounded edges?

[Aravisian]

The easiest solution would be to use NoCSD package:

[HOW TO] Remove csd's on Cinnamon or XFCE4 desktop

With XFCE 4.16 partially changed over to using CSD's and with Cinnamon and other desktop environments that use some Gnome Apps partially using CSD's, some users may want to make their desktop more uniform and use only the proper window manager. PCMan's fork of gtk-mushrooms can easily do this: Package gtk3-nocsd sudo apt-get install -y gtk3-nocsd Reboot. That's it; that's all there is to it.