Bug 282057 – Registered Custom Property of `<color>` type should not accept `initial-value: light-dark()`

• Status: NEW
• Component: CSS

[David Shin]

Created attachment 473035 [details]
Basic Testcase

As in the testcase, when a registered custom property of color type has the initial value using light-dark(), it seems to resolve to the light value. However, light-dark() [depends on color-scheme](https://drafts.csswg.org/css-color-5/#light-dark), which seems to be definitionally not [computationally independent](https://drafts.css-houdini.org/css-properties-values-api/#computationally-independent), which means that the declaration should be dropped.

In the testcase, referencing registered length custom property with 1em initial value uses the fallback value. Referencing a registered color property with light-dark uses the light value, instead of the fallback value.

[Radar WebKit Bug Importer]

<rdar://problem/139020819>

[Ahmad Saleem]

I looked into it and WebKit ToT, Chrome Canary 132 and Firefox Nightly 134 are matching. Am I missing something in order to reproduce this bug?

[Antti Koivisto]

I think this is indeed a bug as the light-dark() function depends on the color-scheme property and so is not computationally independent. Sounds like all browsers get this wrong.

[Tim Nguyen (:ntim)]

`collectComputedStyleDependencies` is the method that needs to change.

`containsColorSchemeDependentColor` is a helper on CSS color types that you can use to get the relevant info.

[Zach Hoffman]

Besides light-dark(), system colors also depend on color-scheme.