Tested in Mint Xfce 19.1 in case of some errors with normal install.
If you ever tried to install the vertex theme, Horst 3180 advises to uninstall it first by copy/pasting these 3 lines one by one in the terminal.
git clone https://github.com/horst3180/vertex-theme
We are going to use the following script to run .autogen.sh.
But we will need some programs to be able to run it. So let us install them.
./autogen.sh --prefix=/usrsudo make install