It appears that applying a font scaling using an em value is double applied when specified in the .root class of a stylesheet attached to a Scene.

Run the below test case. In the first stage the label is styled 1.2em bigger using a direct setStyle on the label. In the second stage a custom stylesheet is added to the scene with a font scaling of 1.1em in the .root class.

When run both labels appear to use the same size font even though their scaling is quite different. I have observed the same behaviour when scaling is applied using setStyle on the root parent in the scene too.

Test class:


import java.io.IOException;
import java.io.Writer;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;

import javafx.application.Application;
import javafx.application.Platform;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.layout.Pane;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;


public class StyleSheetTest extends Application {

@Override
public void start(Stage primaryStage) throws Exception {

primaryStage.setWidth(600);
primaryStage.setHeight(400);
primaryStage.centerOnScreen();

primaryStage.setScene( new Scene(createPane(true)));
primaryStage.show();

new Thread(new Runnable() {
@Override
public void run() {
            try {
             final Path cssFile = Files.createTempFile("test", ".css");
             cssFile.toFile().deleteOnExit();
             Writer w = Files.newBufferedWriter(cssFile, StandardCharsets.UTF_8);
             w.write(".root { -fx-font-size: 1.1em; }");
             w.close();
             Platform.runLater(new Runnable() {
@Override
public void run() {
Stage otherStage = new Stage();
otherStage.setWidth(600);
otherStage.setHeight(400);
otherStage.centerOnScreen();

Scene scene = new Scene(createPane(false));
scene.getStylesheets().add("file:" + cssFile.toString());
otherStage.setScene( scene );
otherStage.show();
}
});
            } catch (IOException e) {
e.printStackTrace();
            }
}
}).start();


}

private Pane createPane(boolean styleBigger) {
      Label label = new Label("Test Label");
      if ( styleBigger ) {
    label.setStyle("-fx-font-size: 1.2em;");
      }

      StackPane sPane = new StackPane(label);
      return sPane;
}

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

}