The theme is intended for dark desktop environments and it inherits Papirus-Dark Icon Theme which is not included in the package.
This icon theme consists of:
actions - taken from Breeze Icon Theme (LGPL-2.1+) dark variant and mildly dimmed
apps - taken from Numix Circle Icon Theme and just a bit from Numix Bevel Icon Theme (probably only terminal icon - can't recall)
devices - taken from Arc Icon Theme
mimes - taken from Numix Icon Theme and slightly unified and dimmed and changed few colors
places - taken from Arc Icon Theme
All credits goes to the appropriate authors.
All the icons - besides actions which are from Breeze Icon Theme (LGPL-2.1+) - are under GPL-3+ license.