Currently it is resolved lazily in render tree. It should be resolved eagerly during style resolution to play well with container queries. This also enables things like animation.
Created attachment 453603 [details] Patch
Created attachment 453626 [details] Patch
Created attachment 453705 [details] Patch
Created attachment 453825 [details] Patch
*** Bug 230964 has been marked as a duplicate of this bug. ***
Created attachment 453840 [details] Patch
Created attachment 453904 [details] Patch
Created attachment 453905 [details] Patch
Created attachment 453907 [details] Patch
Created attachment 453908 [details] Patch
Comment on attachment 453908 [details] Patch v.nice.
Committed r290867 (248098@main): <https://commits.webkit.org/248098@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 453908 [details].
<rdar://problem/89857957>