False positives when using css variables

[ismay]

Variables that match css declarations are being incorrectly interpreted as those declarations and not as variables. See here for further discussion on where exactly it's going wrong.

[clshortfuse]

Original issue sites:

.class {
  width:rem-calc(20px);
}

Passing scss directly into doiuse isn't really supported, nor should it be. scss is a preprocessor. Whatever rem-calc does in SCSS should transform into css before landing in doiuse.

Also, this isn't really CSS variables (which are different thing). This seems like custom CSS functions which aren't part of any spec. We can explore that later if that ever happens.