Now the actual value is new Font(12), but in css ref it is 'null'.
Please, update css ref.

import com.sun.javafx.runtime.VersionInfo;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;
import javafx.application.Application;
import javafx.application.Platform;
import javafx.css.CssMetaData;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.AnchorPane;
import javafx.stage.Stage;

public class Main extends Application {

    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage stage) throws Exception {
        setUserAgentStylesheet(STYLESHEET_MODENA);
        stage.setTitle(VersionInfo.getRuntimeVersion());
        stage.setScene(createScene());
        
        Platform.runLater(new Runnable() {
            @Override
            public void run() {
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException ex) {
                    Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
                }
                Button b = new Button();

                Map<String, CssMetaData> styles = new HashMap<>();
                for (CssMetaData data : b.getCssMetaData()) {
                    styles.put(data.getProperty(), data);
                }

                CssMetaData data = styles.get(getTestedStyle());

                System.out.println("Initial value " + data.getInitialValue(b));
            }
        });
        
        stage.show();
        
    }

    private Scene createScene() {
        return new Scene(new AnchorPane());
    }

    private String getTestedStyle() {
        return "-fx-font";
    }
}