[css-om][css-backgrounds] Serialization of `background: none`

[mozilla-apprentice]

A resolution was made for csswg-drafts/#8496.

[css-om][css-backgrounds] Serialization of `background: none`

• RESOLVED: Move color at the end of the final-bg-layer grammar, to make it serialize as `none`

Discussion.

---

To file a bug automatically for these resolutions, add the bug label to the issue.

If no bug is needed, the issue can be closed.

[dholbert]

I filed https://bugzilla.mozilla.org/show_bug.cgi?id=1821230