🌓 Adds Dark Mode (#210)

* feat(dark mode): set up first set of colors

* feat(dark mode): define state colours

* 🧹

* feat(dark mode): variablify all teh wordz

* feat(dark mode): set colors on body

* feat(dark mode): replace hard coded color value

* feat(dark mode): 🌑

* feat(a11y): update link focus styles

- restores visible focus in windows high contrast mode
- increases visibility in boxes with bg colour

* feat(dark mode): enable postcss

* 💅

* feat(dark mode): add user control

* chore: use generic headline name

* feat(dark mode): hide switch until script loads

* feat(dark mode): increase link contrast

* add content warning to footer nav partial

* feat(dark mode): replace hard coded colour value in alertbox

* feat(dark mode): tone down text colour

* feat(dark mode): properly invert code elements

* 🧹 move box styles into own partial

* feat(dark mode): use darker colour as background for links

assets/css/base.scss

@@ -10,7 +10,7 @@
 
 // 3. Base stuff
 @import 'base/custom-properties', 'base/fonts', 'base/base', 'base/selection',
-  'base/typography', './base/a', 'base/helpers';
+  'base/typography', './base/a', 'base/helpers', 'base/radio-buttons', 'base/code';
 
 // 4. Layout-related sections
 @import 'structures/header', 'structures/footer', 'structures/grid',
@@ -18,7 +18,7 @@
   './structures/definition-content', './structures/definition-navigation';
 
 // 5. Components
-@import 'components/word', 'components/lists', 'components/definitions',
+@import 'components/word', './components/box', 'components/lists', 'components/definitions',
   'components/flag', 'components/alertbox';
 
 // 6. Page-specific styles