https://developer.mozilla.org/en-US/docs/Web/API/CSSMathSum/CSSMathSum
CSSMathSum: CSSMathSum() constructor - Web APIs | MDN
The CSSMathSum() constructor creates a new CSSMathSum object which creates a new CSSKeywordValue object which represents the result obtained by calling add(),...
constructor webcssmathsumapismdn
https://developer.mozilla.org/en-US/docs/Web/API/CSSMathSum/values
CSSMathSum: values property - Web APIs | MDN
The CSSMathSum.values read-only property of the CSSMathSum interface returns a CSSNumericArray object which contains one or more CSSNumericValue objects.
web apiscssmathsumvaluespropertymdn