Setting a style class only for first-level nodes in JavaFX treeTableView

I have a restaurant menu with dishes and categories implemented as a treeTableView in javaFX.

I want to make the the category rows appear different with CSS but I just can't find a way to filter them out and apply a class. Moving the images a bit to the left would also be nice. I also had no luck using a rowFactory. I've seen this answer but I don't understand it.

This is how I fill the table. I've left out the column- and cellfactories.

private void fillDishes(List<Dish> dishes){
    root.getChildren().clear();
    Map<String,TreeItem<Dish>> categoryMap = new HashMap<>();

    for (Category c: allCats) {
        TreeItem<Dish> newCat = new TreeItem<>(new Dish(c.getName(),null,null,null));
        //newCat.getGraphic().getStyleClass().add("category");
        categoryMap.put(c.getName(),newCat);
        root.getChildren().add(newCat);
    }
    for (Dish d: dishes) {
        categoryMap.get(d.getCategory()).getChildren().add(new TreeItem<>(d));
    }
}

TreeTableView uses the rowFactory to create the TreeTableRows. At some time later it assigns a TreeItem to a TreeTableRow. This may happen again with different TreeItems for the same row. For this reason you need to handle changes those changes which can be done by adding a ChangeHandler to the TreeTableRow.treeItem property. If a new TreeItem is assigned to the row, you can check for top-level nodes by checking the children of the (invisible) root item for the row item.

I prefer the approach that does not require searching the child list though. It's possible to compare the parent of the item with the root.

public static class Item {

    private final String value1;
    private final String value2;

    public Item(String value1, String value2) {
        this.value1 = value1;
        this.value2 = value2;
    }

    public String getValue1() {
        return value1;
    }

    public String getValue2() {
        return value2;
    }

}

@Override
public void start(Stage primaryStage) {
    final TreeItem<Item> root = new TreeItem<>(null);
    TreeTableView<Item> ttv = new TreeTableView<>(root);
    ttv.setShowRoot(false);

    TreeTableColumn<Item, String> column1 = new TreeTableColumn<>();
    column1.setCellValueFactory(new TreeItemPropertyValueFactory<>("value1"));

    TreeTableColumn<Item, String> column2 = new TreeTableColumn<>();
    column2.setCellValueFactory(new TreeItemPropertyValueFactory<>("value2"));

    ttv.getColumns().addAll(column1, column2);

    final PseudoClass topNode = PseudoClass.getPseudoClass("top-node");
    ttv.setRowFactory(t -> {
        final TreeTableRow<Item> row = new TreeTableRow<>();

        // every time the TreeItem changes, check, if the new item is a
        // child of the root and set the pseudoclass accordingly
        row.treeItemProperty().addListener((o, oldValue, newValue) -> {
            boolean tn = false;
            if (newValue != null) {
                tn = newValue.getParent() == root;
            }
            row.pseudoClassStateChanged(topNode, tn);
        });
        return row;
    });

    // fill tree structure
    TreeItem<Item> c1 = new TreeItem<>(new Item("category 1", null));
    c1.getChildren().addAll(
            new TreeItem<>(new Item("sub1.1", "foo")),
            new TreeItem<>(new Item("sub1.2", "bar")));

    TreeItem<Item> c2 = new TreeItem<>(new Item("category 2", null));
    c2.getChildren().addAll(
            new TreeItem<>(new Item("sub2.1", "answer")),
            new TreeItem<>(new Item("sub2.2", "42")));

    root.getChildren().addAll(c1, c2);

    Scene scene = new Scene(ttv);
    scene.getStylesheets().add("style.css");

    primaryStage.setScene(scene);
    primaryStage.show();
}

style.css

.tree-table-row-cell:top-node {
    -fx-background: orange;
}

Moving the images a bit to the left would also be nice.

Usually you do this from a custom TreeTableCell returned by a TreeTableColumn.cellFactory. Depending on the behavior you want to implement setting fitWidth/fitHeight may be sufficient, but in other cases dynamically modifying those values based on the cell size may be required.