Typography documentation review and update

[foxintherain]

What

Content review and improvements of typography guide for all brands to identify improvements needed or gaps. Uses new structure, as defined in the styleguide audit.

Why

Typography documentation was created a while ago and needs updating following the styleguide audit.

Done when

• [x] Content has been reviewed
• [x] Improvements have been made
• [x] Updates have been reviewed by UI design team
• [x] Updates have been reviewed by Elements team
• [x] Updates published