Installing KDE themes

Hi,

I have been searching for a material design theme, and I found this https://github.com/varlesh/papirus-pack-kde. Since I couldn’t find any straight forward instructions I’m asking here. How do I install this? Also I have found that there are some themes, in the control center that don’t install properly, instead they download a tar.gz file, and after selecting install from file, it says that it’s not a valid theme. What do I do with these?

Thanks in advance.