CSS Color level 5 introduces the relative color syntax which allows to compute a color based on another one: https://www.w3.org/TR/css-color-5/#relative-colors

This feature is already available in Safari 16.4+ and Chrome will ship it soon.

Currently, this syntax throws an error when using it in a Sass file with a color function known by Sass (using it in oklab works for now due to the lack of support for oklab in Sass and so not treating it like a color at all, but this would change once #2831 will be implemented): https://sass-lang.com/playground/#MTFhJTIwJTdCJTBBJTIwJTIwYiUzQSUyMHJnYihmcm9tJTIwbWFnZW50YSUyMGNhbGMociUyMCUyQiUyMDNkZWcpJTIwZyUyMGIpJTNCJTBBJTdE

Following the design principles of Sass, this syntax should be accepted.