gulp6.js

import cssnano from 'gulp-cssnano';
import esCssModules from 'es-css-modules';

gulp.task('compile-css', ['compile-bootstrap'], () => {
  const cssClass = cssClassGenerator();

  return gulp.src('styles/**/*.css')
    .pipe(postcss([
      esCssModules({
        jsFiles: 'src/index.js',
        generateScopedName: () => cssClass.next().value,
        warnOnUnusedClasses: false,
      }),
    ]))
    .pipe(cssnano({
      discardComments: {
        removeAll: true,
      },
    }))
    .pipe(gulp.dest('dist'));
});