It's possible for certain CSS transition properties to specify a longer list of values than the transition-property property itself. In the case where a custom property is used, we must ensure to fill in the custom property string for the generated Animation object.
rdar://104073160
Pull request: https://github.com/WebKit/WebKit/pull/8473
Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/37853
Committed 258770@main (63d1cc8d95c6): <https://commits.webkit.org/258770@main> Reviewed commits have been landed. Closing PR #8473 and removing active labels.