Spacing 👾 (#321)

* Spacing: Add margin variables throughout

Attempt to match figma spacing with headings
Add variables for ol and ul colours

* Spacing: Add callout and tab group spacing

* Icons: Fix icon usage in callouts

* Callout: Fix margin and whitespace in side callouts

* Typography: Wrap headers in .content class

Fix h1s on list pages not lining up with images

* Homepage: Fix card text overflow

* Content: Fix narrow content shifting between pages

* Layout: Fix outer container padding

Author: nginx-jack