In the 2021 draft of CSS variables 1, it was explicitly specified that custom properties should be serialized exactly as specified by the author, including whitespace. This is counter to the behavior widely implemented by browsers before that point, in which whitespace in the serialized property values was collapsed into a single space character.
Based on the old browser behavior, Sass also collapses custom property whitespace in order to emit smaller stylesheets and avoid unsightly whitespace artifacts from custom properties that include newlines. However, that is now contrary to the CSS specification and so a CSS compatibility issue. Browsers currently somewhat follow the specification, preserving whitespace (and comments) everywhere except for the beginning and (on Chrome) the end of property values.
I do feel some amount of hesitation here, though. Although Sass is committed to meticulous CSS compatibility, I don't know of any evidence of an actual use-case for not folding whitespace; the motivating example given in the spec for preserving the exact format focuses on non-whitespace characters. What's more, it's likely that this would be seen as a behavior regression for the users (likely a substantial majority) who want Sass to emit minimal or visually-attractive stylesheets.
See also cssnano/cssnano#1457 (comment), where this same concern is being considered by cssnano.
In the 2021 draft of CSS variables 1, it was explicitly specified that custom properties should be serialized exactly as specified by the author, including whitespace. This is counter to the behavior widely implemented by browsers before that point, in which whitespace in the serialized property values was collapsed into a single space character.
Based on the old browser behavior, Sass also collapses custom property whitespace in order to emit smaller stylesheets and avoid unsightly whitespace artifacts from custom properties that include newlines. However, that is now contrary to the CSS specification and so a CSS compatibility issue. Browsers currently somewhat follow the specification, preserving whitespace (and comments) everywhere except for the beginning and (on Chrome) the end of property values.
I do feel some amount of hesitation here, though. Although Sass is committed to meticulous CSS compatibility, I don't know of any evidence of an actual use-case for not folding whitespace; the motivating example given in the spec for preserving the exact format focuses on non-whitespace characters. What's more, it's likely that this would be seen as a behavior regression for the users (likely a substantial majority) who want Sass to emit minimal or visually-attractive stylesheets.
See also cssnano/cssnano#1457 (comment), where this same concern is being considered by cssnano.