Using Theme Generator, you can generate beautiful light and dark themes that can be exported to GtkSourceView Style Schemes or a single light and dark theme that can be used with ThiefMD and Ulysses. It is written in vala and released under MIT License. This app comes with light and dark Color Pallets, color picker, Markdown Elements and the styling options and more. You can open the exported themes with ThiefMD and Ulysses.
How to Install Theme Generator on Ubuntu Linux
Theme Generator is available as flatpak package from flathub. First install flathub and flatpak on your system and restart it after the successful installation. After that open the terminal command line software and run below Theme Generator flatpak install command. It will install the latest version of Theme Generator on your system.
flatpak install flathub io.github.thiefmd.themegenerator
Now open the app using below command. You can also open it via the applications menu.
flatpak run io.github.thiefmd.themegenerator
And uninstall it if you don’t like it.
sudo flatpak uninstall io.github.thiefmd.themegenerator