[csswg-drafts] [css-images-4] Add `light-dark-image()`, or generalize `light-dark()` for images too? (#12513)

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

== [css-images-4] Add `light-dark-image()`, or generalize `light-dark()` for images too? ==
The existing `light-dark()` function gives a very easy way to select different colors based on the used color scheme on an element. In #10577 we're discussing adding an `if()` test to generalize that, so you can vary *any* value based on the used color scheme (for example, `font-weight: if(color-scheme(dark): bold, else: normal);`). This is a little more verbose, but it's a rarer use-case, so that's all right.

In <https://github.com/w3c/csswg-drafts/issues/10577#issuecomment-2887663097>, Emilio suggests that varying CSS images based on color scheme is a common enough use-case to be worth addressing as simply as colors. (Several other people have argued this as well in similar issues.) I agree; any background image I apply in a light-mode stylesheet almost certainly has to be changed in a dark mode stylesheet.

I see two possible ways to do this:

1. Just extend the grammar of `light-dark()`, to `light-dark( <color>#{2} | <image>#{2} )`. If you supply two colors, it returns a color; if you supply two images, it returns an image.
2. Add a `light-dark-image( <image>#{2} )` function, which is identical to `light-dark()` but always returns an image, instead of always returning a color.

I don't have a strong opinion in this regard. Folding them both together into a single function like in (1) is convenient, but starts implying that it might cover even more types, and we don't want to suggest that. Duplicating the functionality with a similarly-named function like in (2) is simple, but also a little bit more verbose.

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/12513 using your GitHub account


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Received on Tuesday, 22 July 2025 18:23:23 UTC