Remove default font styles from cookie banner Sass

[vanitabarrett]

Closes #2358

What

Remove the default font styles (setting the font and font-size) from the cookie banner Sass.

Why

With the default font styles present, it's very difficult to spot if you forget to add the relevant govuk-body styles to any html you pass into the component. We had missed this ourselves when we added the cookie banner to the design system.

Screenshots

Before change - cookie banner with html, without govuk-body classes

After change - cookie banner with html, without govuk-body classes

After change - cookie banner with html, with the correct govuk-body classes

After change - in the Design System

This work was prompted by when we forgot to add our own styling classes to the cookie banner on the design system site, which resulted in slightly incorrect text spacing. This is what the design system cookie banner would now look like if we forgot to add the relevant classes:

Details of breaking change

This is a breaking change because any users who are relying on the default styles will see unstyled text in their cookie banner when they update. Users will need to add the correct classes to style the text - this will probably involve adding the govuk-body class to any HTML paragraph tags they're passing through to the component.

• which users are affected: users who are using the cookie banner component and passing their own html into the cookie banner component
• the change that’s been made: we've removed the default font styles from the cookie banner component
• changes users will have to make: users will need to make sure that any HTML they pass into the cookie banner component has the appropriate classes/styles (e.g: govuk-body)
• impact of users not making those changes: cookie banners will appear with unstyled text

[hannalaakso]

Makes sense, thanks @vanitabarrett 👍

[EoinShaughnessy]

Just suggesting a last tiny change, otherwise content is golden. :)