The Server Look and Feel specifies the Look of the widgets. Note that the Look of a widget may depend on its StyleSet property, which can be set at design-time, and can be changed at runtime.
J661 allows to specify the Look of widgets in a configuration file. THis Look and Feel is specified through the ui and lf Server configuration properties. The Look and file also depends on the UI framework used to implement the Server graphics.
Swing look and Feel
The Swing Look and Feel for the Server is based on Java Swing Look and Feels. Generally Swing Look and Feels used in the Server won't implement the notion of StyleSet except the Synth2 Look and Feel.
JavaFX look and Feel
The JavaFX Look and Feel for the Server is based on the JavaFX CSS Look specifications.
See also
Look and Feel configuration: The Look and Feel configuration file specifies the cockpit configuration for a SuperLayer Window Manager