This is a copy of Mint-X, one of the built-in desktop themes for Linux Mint. It includes some changes I've made to learn how to create themes.
The original code (among other things) is here: https://github.com/linuxmint/mint-themes
Note: I'm not affiliated with Linux Mint, I just use their software.
You'll need the Cinnamon variant of Linux Mint. I've only tested this theme on version 20.3.
Clone this repo into ~/.themes/. Then run the install.sh script.
To reload the theme, run ./swap-themes.sh. This will briefly swap the theme
to a different one and back to osx. Most apps will redraw in response.
You'll probably want the GTK inspector for debugging. Run:
apt install libgtk-3-dev
apt install dconf-editor
And enable the inspector by running dconf-editor and changing
org.gtk.Settings.Debug.enable-inspector-keybinding to true.
Then you can hit ctrl+shift+I in any GTK app to open the inspector.