CSS grid unit fr is not supported

[geetkibo]

Hello,
We're facing a weird issue with CSSList where it's considering valid CSS to be invalid and raising linting error. The issue is with fr unit of css grid which is not being passed as valid by lint checking mechanism. I've also attached a screenshot of the error.
I wanted to ask does maintainers of CSSLint have a plan to fix this issue, if not then can someone suggest a workaround.
Thanks.

Expected behaviour: Valid CSS grid unit like fr should get passed from lint checking.
Current behaviour: Linter doesn't consider fr unit to be valid CSS and raised error message "Expected RBRACE at line XX".

Screenshot of error