it's the 3. example, offending line:

private final StyleableProperty<Boolean> selected =
         new SimpleStyleableBooleanProperty(this, "selected", "my-selected");

error: the constructor (...) is undefined

The first parameter needs to be of type CssMetaData.

javadoc:
https://openjfx.io/javadoc/11/javafx.graphics/javafx/css/StyleablePropertyFactory.html