Based on the Mint-Y Linux Mint themes. WIP
There are several different ways to install themes in Kvantum, the easiest method is to just install it from the Kvantum Manager.
You can also copy the themes directly to ~/.config/Kvantum/
or /usr/share/Kvantum/.
If you have downloaded directly from the git repo, building these will be necessary if you wish to use the themes other than the base Mint-Y and Mint-Y-Dark.
cd into this directory and run ./build_subthemes.py.