Currently, CSSTransformValue subclasses only take CSSUnitValues, but not CSSMathValues that simplify to a valid CSSUnitValue. For example, CSSTranslation [1] accepts <length-percentage>s, so it should not only accept things like CSS.px(1), but also new CSSMathSum(CSS.px(1), CSS.px(1)).
The logic for matching against things like <length> are already in the codebase, so this should be straightforward.
[1] https://drafts.css-houdini.org/css-typed-om-1/#dom-csstranslation-csstranslation
Comment 1 by shend@chromium.org
, Nov 29 2017