Javafx FXML - How to make GridPane the same height as the window? - javafx

Question

The intended outcome is that the element at (0,0) should resize to fill up the empty space around the GridPane. I have looked at other questions similar to this and the answers have not worked - I am trying to make the GridPane the same height as the VBox that is inside of. It works horizontally using hrow="always", but using vgrow="always" has not had the same affect.
I have coloured the VBox that the GridPane is within a different colour, so it is clear that the VBox is taking up the height of the stage, and therefore the GridPane is the issue here. How could I stretch the vertical height similar to the horizontal width?
<?xml version="1.0" encoding="UTF-8"?>
<?import java.net.*?>
<?import javafx.geometry.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.text.*?>
<?import javafx.scene.SubScene?>
<?import javafx.scene.Group?>
<VBox
fx:controller="Controller"
xmlns:fx="http://javafx.com/fxml"
styleClass="root" >
<MenuBar>
<menus>
<Menu text="File">
<items>
<MenuItem text="New" />
<MenuItem text="Save" />
<MenuItem text="Load" />
</items>
</Menu>
</menus>
</MenuBar>
<GridPane hgap="10" vgap="10">
<rowConstraints>
<RowConstraints vgrow="ALWAYS" />
</rowConstraints>
<columnConstraints>
<ColumnConstraints hgrow="ALWAYS" />
</columnConstraints>
<gridLinesVisible>true</gridLinesVisible>
<SubScene
GridPane.columnIndex="0" GridPane.rowIndex="0"
GridPane.rowSpan="6">
<root>
<Group />
</root>
</SubScene>
<Button text="Add"
GridPane.columnIndex="1" GridPane.rowIndex="0" />
<Button text="Edit"
GridPane.columnIndex="2" GridPane.rowIndex="0" />
<Button text="Delete"
GridPane.columnIndex="3" GridPane.rowIndex="0" />
<ScrollPane
GridPane.columnIndex="1" GridPane.rowIndex="1"
GridPane.columnSpan="3" />
<Label text="Speed"
GridPane.columnIndex="1" GridPane.rowIndex="2" />
<Slider
GridPane.columnIndex="2" GridPane.rowIndex="2"
GridPane.columnSpan="2" />
<Label text="Gravity"
GridPane.columnIndex="1" GridPane.rowIndex="3" />
<TextField
GridPane.columnIndex="2" GridPane.rowIndex="3"
GridPane.columnSpan="2" />
<HBox
GridPane.columnIndex="1" GridPane.rowIndex="4">
<Button text="<<" />
<Button text="<" />
</HBox>
<Text text="0.00"
GridPane.columnIndex="2" GridPane.rowIndex="4" />
<HBox
GridPane.columnIndex="3" GridPane.rowIndex="4">
<Button text=">" />
<Button text=">>" />
</HBox>
<Button text="Start"
GridPane.columnIndex="2" GridPane.rowIndex="5" />
</GridPane>
<stylesheets>
<URL value="#style.css" />
</stylesheets>
</VBox>