feat: add theme menu
- Update styles for theming
- Add dark, system, & light mode buttons
- Add
is:inline
theming script to<head>
to actually remove FOUT?! - The system theme is the default for now. Dark mode users rejoice!
The way the theming (mainly CSS) is setup is very inspired by Ryan Mulligan (ryanmulligan.dev)...except without all the dope color options. Thank you so much for being a smartypants :)