Test name: SwingSet2.jar  
Product(s) tested: JDK8u202 b04(64bit) , JDK12b21
OS/architecture:Oel7.5 uek x64 
VM Options:-Djdk.gtk.version=3 -Djdk.gtk.verbose=true 

1. Run the demo with the gtk version set at command line to 2 and then to 3.
2. Compare the rendering of the JScrollPane demo
Expected: Scrollbar is shown the same with the scrollbar thumb being visible.
Actual: on GTK3.0 scrollbar track is not visible.

Seen on jdk8u202b04 as well as jdkb12.