This tutorial [0] / [1] (using LESS) worked well for me. I recently did the upgrade from 3.3.6 - 3.3.7. You create a directory just outside bootstrap and refer

This tutorial [0] / [1] (using LESS) worked well for me. I recently did the upgrade from 3.3.6 - 3.3.7. You create a directory just outside bootstrap and reference that from `bootstrap.less` inside the bootstrap core to override the bootstrap variables. Then you just have to modify `bootstrap.less` in the core bootstrap directory after upgrading. [0]: https://www.smashingmagazine.com/2013/03/customizing-bootstrap/ [1]: https://github.com/thomaspark/bootswatch/