Ensure values are ordered consistently in your CSS.
With npm do:
npm install postcss-ordered-values --save
Some CSS properties accept their values in an arbitrary order; for this reason, it is entirely possible that different developers will write their values in different orders. This module normalizes the order, making it easier for other modules to understand which declarations are duplicates.
For more examples, see the tests.
See the PostCSS documentation for examples for your environment.
MIT © Ben Briggs