Add feature: CssFunction

[andruud]

Specification

https://drafts.csswg.org/css-mixins-1/#function-rule

Description

Custom functions in CSS.

Documentation

N/A

Browser support

Planned for Chrome M139 (stable ~August 2025, schedule).

[captainbrosset]

Some resources I found on this:

• https://css-tricks.com/functions-in-css/
• https://issues.chromium.org/issues/325504770
• https://us19.campaign-archive.com/?u=80219aa68d7bad77b9fd2eb93&id=aac7298a5b
• https://chromestatus.com/feature/5179721933651968

[captainbrosset]

I'll make an attempt at creating a feature for this.