bb0c02e004
All color functions support a from keyword as part of the relative color syntax. https://drafts.csswg.org/css-color-5/#relative-colors This patch adds a pref layout.css.relative-color-syntax.enabled that is off by default. We start passing tests that only check for the validity of the `from` keyword in different color functions. Differential Revision: https://phabricator.services.mozilla.com/D206374