configureCssLoader(callback) {
        webpackConfig.configureCssLoader(callback);

        return this;
    }
Configure the css-loader.

https://github.com/webpack-contrib/css-loader#options

```
Encore.configureCssLoader(function(config) {
    // change the config
    // config.minimize = true;
});
```

@param {OptionsCallback<object>} callback
@returns {Encore}