mediawiki-skins-Vector/doc/adr/0002-use-css-custom-properties.md
Jan Drewniak 2223cb8c1b Introduce CSS custom properties under font-size feature flag
Introduces CSS custom properties for the purposes
of enabling client-side customizable font sizes.

CSS custom properties are contained in a Less file,
which imports values from Codex and converted them to rems
using the Less unit() function.

Includes ADR on CSS custom properties decisions.

Bug: T348984
Change-Id: Ic5e62d55f3c3585fe3a00e41f29f88d3a2f7470b
2023-10-24 14:33:33 +00:00

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# 2. Use CSS custom properties in Vector
Date: 2023-10-23
## Status
Accepted.
## Context
In the context of the [Accessibility for Reading project](https://www.mediawiki.org/wiki/Reading/Web/Accessibility_for_reading) we needed a way to enable font-size customization in Vector in a scalable way. CSS custom properties were the mechanism chosen to enable this functionality. Full discussion available on [T346072](https://phabricator.wikimedia.org/T346072).
## Decision
CSS Custom properties will be implemented in Vector on a very tightly scoped basis. The implementation assumes that we will eventually want to up-stream CSS custom properties to MediaWiki core/Codex.
In order to facility an eventual migration, the following implementation measures will be taken:
- CSS custom properties will be used *only* when needed for client-size customization.
- CSS custom properties will be grouped in the following file
`resources/skins.vector.styles/CSSCustomProperties.less`.
- CSS custom properties will maintain consistency with the naming convention of Codex design tokens.
- When possible, we'll assign CSS custom properties to existing Codex token values.
## Consequences
CSS Custom properties will be marked as `@private` and `@experimental` in the spirit of the [Stable interface policy/Frontend](https://www.mediawiki.org/wiki/Stable_interface_policy/Frontend) in order to discourage usage outside of Vector. This could be changes to `@internal` if usage outside of Vector is deemed necessary.