Bourbon Fundamentals - Triangle Mixin

This topic is for the [Triangle Mixin][] exercise in the [Bourbon Fundamentals][] trail. Post any questions, corrections, or pointers you have to share with other Upcase subscribers.
[Triangle Mixin]: https://exercises.upcase.com/exercises/triangle-mixin
[Bourbon Fundamentals]: https://thoughtbot.com/upcase/bourbon-fundamentals