This is an example repo for adding webpack to Middleman via the external pipeline. Accompanying Blog Post.
Javascript and CSS live under assets. The javascript files form the entrypoint. Include whatever CSS you need from there and it will be extracted into the built site with the same name as the entypoint file you used.
Images are not managed via Webpack.
$ bundle install
$ yarn installThen use the usual Middleman commands e.g. middleman server or middleman build.
Edit the entry section of webpack.config.js as necessary.
This uses SASS and PostCSS but you can alter those loaders to fit your taste.