materia-gtk-theme : Materia is a Material Design theme for GNOME/GTK based desktop environments. ( https://github.com/nana-4/materia-theme )
materia-kde : This is a port of the popular GTK theme Materia for the Plasma 5 deskto ( https://github.com/PapirusDevelopmentTeam/materia-kde )
Add an ebuild in portage :
The ebuild is now in the portage tree.
You can also use layman : emerge layman then layman -a gig
For Paludis use this rsync : rsync://gentoo.zugaina.org/gig-portage
If you have a problem : ycarus(-at-)zugaina.org