This is a theme injector that doesn't require patching the Discord client. As a bonus, this means that you can easily use themes in Discord's web application, but the downside is that you have to apply your theme manually every time you start Discord.
$ cargo run [...] Listening on: http://127.0.0.1:12345/
- A browser should open at the given URL
- Choose the theme you want to apply
- Hit 'Copy JS'
- Paste into Discord's DevTools console (you can hit Ctrl + Shift + I to open this)