Source (link to git-repo or to original if based on someone elses unmodified work): https://github.com/PapirusDevelopmentTeam/materia-kde
Materia KDE - it's port Materia GTK Theme for Plasma 5 desktop.
NOTE: Look and Feel settings not applied fully. Please check settings manually.
Also not forget install Kvantum engine:
and Materia Kvantum theme: