Error message looks like this:

var api = require("!./node_modules/[email protected]@style-loader/dist/runtime/injectStylesIntoStyleTag.js");

If you’re using Storybook, or multiple webpack configs of dev/prod, or simply multiple rules… Either way, this error means you’ve specified rules for CSS more than once.

For example, Storybook already has a set of default rules for various file types, and CSS is one of them, so you cannot specify custom CSS rules again.