Original description (v. 0.1):
"A KDE window decoration (KWin Aurorae) in 2 colour variants:

- Blue Breeze
- Grey Arc

Released under CC BY-SA 4.0 license."

You should disable the blur effect for better quality, go to system settings > Desktop Behaviour > Desktop Effects : Under "Appearance" untick "Blur".

Thank you Giacomo Barazzetti for the great work. Visit the original here: https://www.opendesktop.org/p/1229514/