[Webkit-unassigned] [Bug 282057] New: Registered Custom Property of `<color>` type should not accept `initial-value: light-dark()`

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=282057

            Bug ID: 282057
           Summary: Registered Custom Property of `<color>` type should
                    not accept `initial-value: light-dark()`
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Unspecified
                OS: macOS 15
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: dshin at mozilla.com
                CC: koivisto at iki.fi

Created attachment 473035

  --> https://bugs.webkit.org/attachment.cgi?id=473035&action=review

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.

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