You can find this setup as an example on github: https://github.com/programmiri/brunch-setup-bootstrap4
[…]
Bootstrap can be used very modular. I don’t import the complete Bootstrap CSS. Instead I use import in the _config.scss to only get the components I want to use. In the end my CSS files only contains what I really need and use. Neat and clean - that’s how I like it!
[…]