CSS Tools

CSS is simple to tokenise and full of context that a naive tool gets wrong. A colon separates a property from its value, except inside a url(), a data URI or a media feature, where it means something else. Minifying or formatting without tracking that context breaks values silently.

Colour is where most CSS calculation happens. Converting between hex, RGB, HSL and OKLCH is straightforward arithmetic, but the newer perceptual spaces are worth the trouble: OKLCH lightness corresponds to how light a colour actually looks, so adjusting it does not shift the hue the way HSL does.

Contrast ratios are the other calculation that matters, because they are a requirement rather than a preference. WCAG defines them in terms of relative luminance, which is not the same as HSL lightness, two colours with identical lightness can have very different contrast against white.