Something I learned the hard way yesterday ... JavaFX ships with JDK 7, but it’s not in the classpath. This image shows the solution for when you want to use JavaFX in a Scala/SBT application. You can also just copy the JavaFX jar file to your SBT lib folder, if you prefer. I found this answer on the ScalaFX website.
By Alvin Alexander. Last updated: September 14 2016