undefined variable issues as Webpacker compiles the Sass stylesheets. Interestingly enough it doesn't prevent the build completing but it's still just an annoying error.
It turns out this was because of the location I was placing my Sass files. My pack was located in an
What you'll need to do it move your styles up a directory, into just
The boilerplate for the blank
application.js file acually does warn you that the