Update Tailwind and Dark Mode

See this warning when building on Netlify:

```
3:44:51 PM: warn - The `darkMode` option in your Tailwind CSS configuration is set to `false`, which now behaves the same as `media`.
3:44:51 PM: warn - Change `darkMode` to `media` or remove it entirely.
3:44:51 PM: warn - https://tailwindcss.com/docs/upgrade-guide#remove-dark-mode-configuration
```