spec: https://w3c.github.io/csswg-drafts/css-backgrounds/#the-background

We often run into situations where background-color has already been set for an element or component, and in a separate class we want to also add a background image to it.

In order to do this without overriding the color, we have to use the background-image property specifically.

Then we need to size, position, no-repeat it and that's 3 more longhand properties.

Add two bg images and we're managing parallel arrays in every longhand property above to avoid overriding the background-color set elsewhere.

It gets pretty tedious very quickly.

Fortunately, the spec already defines a <bg-layer> so it may not be a big ask to add background-layers as a shorthand property that defines everything for a background, excluding background-color.

background-layers = <bg-layer># | none

(suggesting plural background-layers even though the longhand bg properties are singular since they predate multiple image layers)

Thank you!