Remove references to 14 on the typography scale from guidance

[owenatgov]

What

Review and remove references to 14 on the typography scale from guidance on the website. There are currently 2 references to 14 on the website:

1. The font size override classes
2. The typography section of how to translate govuk-frontend-toolkit mixins to govuk-frontend

Why

As part of https://github.com/alphagov/govuk-design-system/issues/2289, we should consider iterating our guidance to no longer recommend 14 on the font scale in anticipation of it's removal from govuk-frontend. We would need to do this anyway, but there's potentially an opportunity to do some of it sooner.

Who needs to work on this

The team?

Who needs to review this

Content designers

Done when

• [ ] Assess if we should remove the above listed instances
• [ ] Make changes to the website (if necessary)
• [ ] Let the community know (if necessary)

[owenatgov]

The general feeling from the team at the moment:

• The first instance seems very non-controversial to remove
• The second instance is trickier as it means 4.X users moving a project off of frontend toolkit now don't have an alternative if they are trying to translate a project that used one of the 14px mixins. There's an unknown weighting here around how much grief this would cause given that we're removing compatibility mode in 5.0. A potential compromise is having a paragraph above the advising users that 14 isn't a recommended font size and to use 16 instead.