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const styles = require('!!file-loader!./styles.css');
In Webpack 4, the "!!" before a loader in the webpack configuration file is called the "bang-bang" loader syntax. It is used to override the configuration specified in the webpack configuration file for a specific loader.
Here’s the link to the official Webpack documentation on loaders:
you can find a section called "Inline" that explains how to use the "bang-bang" loader syntax to override loader configuration.