FULL PRODUCT VERSION :
java version "1.8.0_112"
Java(TM) SE Runtime Environment (build 1.8.0_112-b15)
Java HotSpot(TM) Client VM (build 25.112-b15, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Windows 7 64-bit

A DESCRIPTION OF THE PROBLEM :
If root element style set to something like "-fx-font-size: 24px"), all nodes are resized as expected. If however a percentage or em-value is used, e.g. "-fx-font-size: 200%", the header area of a TabPane is not resized and clips the tab labels.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
See source at
https://gist.github.com/dmitryleskov/7b35c42484cbc852134687298e8eb738

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
TabPane header area properly resized to show tab labels
ACTUAL -
TabPane header area size stays uncheged, resulting in tab labels being clipped out.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
package sample;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception {
        Tab tab1 = new Tab("Tab 1", new Button("Click me!"));
        Tab tab2 = new Tab("Tab 2",
                new VBox(new Label("Label"),
                         new TextArea("Some text")
                )
        );
        TabPane root = new TabPane(tab1, tab2);
        primaryStage.setScene(new Scene(root, 320, 200));
        primaryStage.show();
        // root.setStyle("-fx-font-size: 24px"); // This works
        root.setStyle("-fx-font-size: 200%"); // This does not
    }

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

CUSTOMER SUBMITTED WORKAROUND :
Use absolute units