Bourbon Fundamentals - Border Width, Padding, and Margin Mixins

This topic is for the [Border Width, Padding, and Margin Mixins] exercise in the [Bourbon Fundamentals] trail. Post any questions, corrections, or pointers you have to share with other Upcase subscribers.
[Border Width, Padding, and Margin Mixins]: https://exercises.upcase.com/exercises/border-width
[Bourbon Fundamentals]: Bourbon Fundamentals | Online Tutorial by thoughtbot