Adding full dark mode to docs page

[fymmot]

Not sure if this is something you want or not. But I extended the theme switch so it applies to the entire docs page.

• Listens to user preferences via prefers-color-scheme on page load.
• Manual switch (theme toggle button) persists setting via localStorage
• New dark mode color variables in bamboo.css
• New dark mode prism theme

You can see a preview here: https://inclusive-dates-v2-git-docs-theme-fymmot.vercel.app/

Feel free to merge or discard!

[Sqrrl]

Thanks. Very cool. Merged and deployed.