https://drafts.css-houdini.org/css-properties-values-api/#fallbacks-in-var-references
<rdar://problem/103799338>
Pull request: https://github.com/WebKit/WebKit/pull/8116
Committed 258373@main (6dabb8f934a3): <https://commits.webkit.org/258373@main> Reviewed commits have been landed. Closing PR #8116 and removing active labels.