Yes I am using this PostCSS plugin: https://plugins.jetbrains.com/plugin/8578-postcss-support

But it's flawed. PostCSS is itself a host for plugins. So a WebStorm PostCSS plugin would need to allow user to select the PostCSS plugins that they are using.

Case in point: I use postcss-simple-vars but the WebStorm plugin assumes I use postcss-custom-properties. And so it fails me.