[csswg-drafts] Pull Request: [scroll-animations] Add css syntax for element-based offset

majido has just submitted a new pull request for https://github.com/w3c/csswg-drafts:

== [scroll-animations] Add css syntax for element-based offset  ==
Add css syntax to for element-based offsets.

Some notes:
 - <<id-selector>> is required and is expect to be the first argument.
 - both edge and threshold are optional can can be provided in any order.



See https://github.com/w3c/csswg-drafts/pull/5264