To reproduce:

Run FX without "-Dprism.fontdir=<path to fonts lib + config file>" property set and you'll get the following exception:

Exception in thread "JavaFX Application Thread" java.lang.NoClassDefFoundError: Could not initialize class javafx.scene.CssStyleHelper
at javafx.scene.Node.impl_processCSS(Node.java:8877)
at javafx.scene.Parent.impl_processCSS(Parent.java:1250)
at javafx.scene.Node.processCSS(Node.java:8732)
at javafx.scene.Scene.doCSSPass(Scene.java:561)
at javafx.scene.Scene.access$3700(Scene.java:198)
at javafx.scene.Scene$ScenePulseListener.pulse(Scene.java:2370)
at com.sun.javafx.tk.Toolkit.firePulse(Toolkit.java:330)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:479)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:460)
at com.sun.javafx.tk.quantum.QuantumToolkit$13.run(QuantumToolkit.java:327)
at com.sun.glass.ui.lens.LensApplication$RunnableEvent.dispatch(LensApplication.java:182)
at com.sun.glass.ui.lens.LensApplication._runLoop(LensApplication.java:860)
at com.sun.glass.ui.lens.LensApplication.access$1800(LensApplication.java:58)
at com.sun.glass.ui.lens.LensApplication$4.run(LensApplication.java:917)
at java.lang.Thread.run(Thread.java:744)