gulpfile.js

const gulp = require('gulp')
const gulpless = require('gulp-less')
const postcss = require('gulp-postcss')
const debug = require('gulp-debug')
var csso = require('gulp-csso')
const autoprefixer = require('autoprefixer')
const NpmImportPlugin = require('less-plugin-npm-import')

gulp.task('less', function () {
  const plugins = [autoprefixer()]

  return gulp
    .src('src/themes/*-theme.less')
    .pipe(debug({title: 'Less files:'}))
    .pipe(
      gulpless({
        javascriptEnabled: true,
        plugins: [new NpmImportPlugin({prefix: '~'})],
      }),
    )
    .pipe(postcss(plugins))
    .pipe(
      csso({
        debug: true,
      }),
    )
    .pipe(gulp.dest('./public'))
})