[csswg-drafts] [css-backgrounds] <color> in <shadow> should default to currentcolor

upsuper has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-backgrounds] <color> in <shadow> should default to currentcolor ==
Currently the spec says:
> Specifies the color of the shadow. If the color is absent, the used color is taken from the color property.

It seems to behave like `currentcolor` nowadays, but it would have different behavior in terms of interpolating. I think we should probably make it default to `currentcolor` instead. I see no reason we need a separate no-color value case.

(It's not clear to me whether it should go to level 3 or 4.)

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/2766 using your GitHub account