-fx-hgap & -fx-vgap does not work for flowpane

defining hgap and vgap within css has no effect

.main #imagesPane {
    -fx-hgap: 4;
    -fx-vgap: 4;
}

defining in fxml works as expected
<ScrollPane VBox.vgrow="ALWAYS" fitToHeight="true" fitToWidth="true">
                        <FlowPane fx:id="imagesPane" VBox.vgrow="ALWAYS" vgap="4" hgap="4" />
                    </ScrollPane>