I am not sure whether CSS in JavaFX is supposed to be case sensitive or insensitive. The JavaFX CSS Reference Guide says: Boolean values can either have the string value of "true" or "false", the values are case insensitive as all CSS is case insensitive. The book Learn JavaFX 8 says: The Style class names in JavaFX are case sensitive.

However, using the following CSS:

    .root {
        -sidebar-R: #FF0000;
        -sidebar-L: #00FF00;
    }

and Java code:

    group.setStyle("-sidebar: -sidebar-R;");

work fine together, unless the undelying css file is compiled to a bss file. I observed that in the bss file, all CSS names are converted to lowercase. Within the compiled bss file, -sidebar-R can not be resolved any more!

Of course, the workaround and best practise is to not use uppercase letters in CSS at all - but the different behavior between css and bss is confusing.