In the test below padding for TabPane is set. Execute the test and change the tab side - as you can see tabs look correct for top side only. Other sides fail. The tab-header-area seems to ignore padding completely.

tabPane.css:

.tab-pane {
    -fx-padding: 20;
}

.tab-pane > .tab-header-area{
    -fx-background-color: cyan;
}

.tab-pane > .tab-content-area{
    -fx-background-color: yellow;
}



public class TabPaneTest extends Application
{
  public static void main(String[] args)
  {
    Application.launch(args);
  }

  @Override
  public void start(Stage stage)
  {
    Parent root = createContentPane();
    root.getStylesheets().add(getClass().getResource("/test/tabpane/tabPane.css").toExternalForm());
    Scene scene = new Scene(root, 1000, 800);
    stage.setScene(scene);
    stage.setTitle(getClass().getSimpleName());
    stage.show();
  }

  private Parent createContentPane()
  {
    TabPane tabPane = new TabPane();
    tabPane.getStyleClass().add(TabPane.STYLE_CLASS_FLOATING);
    
    tabPane.getTabs().add(createTab("Tab 1", new StackPane()));
    tabPane.getTabs().add(createTab("Tab 2", new StackPane()));
    tabPane.getTabs().add(createTab("Tab 3", new StackPane()));
    tabPane.getSelectionModel().selectLast();
    
    ComboBox<Side> combo = new ComboBox<>();
    combo.setItems(FXCollections.observableArrayList(Side.values()));
    combo.setValue(tabPane.getSide());
    combo.valueProperty().addListener((o, ov, nv) -> tabPane.setSide(nv));

    CheckBox cb = new CheckBox("Floating");
    cb.setSelected(true);
    cb.selectedProperty().addListener((o, ov, nv) -> {
      if (nv)
        tabPane.getStyleClass().add(TabPane.STYLE_CLASS_FLOATING);
      else
        tabPane.getStyleClass().remove(TabPane.STYLE_CLASS_FLOATING);
    });
    
    VBox optionPane = new VBox(5);
    optionPane.getChildren().add(combo);
    optionPane.getChildren().add(cb);
    optionPane.setStyle("-fx-padding:5; -fx-background-color: #0001");
    
    BorderPane p = new BorderPane();
    p.setCenter(tabPane);
    p.setRight(optionPane);
    
    return p;
  }

  private Tab createTab(String name, Node content)
  {
    Tab tab = new Tab();
    tab.setText(name);
    tab.setContent(content);
    return tab;
  }
}