Creating your own themes
A good way to start creating your themes is copying one of the default themes and renaming it to your favorite name.Then, start changing the valus of each option. After you're done. change the theme value in the config file to the name of your new theme and restart Anki
Anki's menu bar ➡️ tools ➡️ add-ons choose "Beautify Anki" then > Configuration