When forming a CSSDeclaration, the .getProperty is always formed in lowercase.

This error is critical when we are dealing with variables.

--A != --a

And when call .getExpressionAsCSSString, the case is respected, as a result, we lose the relationship

Reproducing an error: https://jsfiddle.net/dauhk27r/