MainWindow.fxml

<?xml version="1.0" encoding="UTF-8"?>

<?import java.net.URL?>
<?import javafx.geometry.Insets?>
<?import javafx.scene.Scene?>
<?import javafx.scene.control.Menu?>
<?import javafx.scene.control.MenuBar?>
<?import javafx.scene.control.MenuItem?>
<?import javafx.scene.image.Image?>
<?import javafx.scene.layout.StackPane?>
<?import javafx.scene.layout.VBox?>
<?import javafx.scene.control.TabPane?>
<?import javafx.scene.control.Tab?>
<?import javafx.scene.layout.HBox?>

<fx:root type="javafx.stage.Stage" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1"
         title="Jarvis" minWidth="1000" minHeight="600" onCloseRequest="#handleExit">

    <icons>
        <Image url="@/images/jarvis.png"/>
    </icons>

    <scene>
        <Scene>

            <stylesheets>
                <URL value="@cssfiles/CustomLightTheme.css"/>
<!--                <URL value="@CustomExtensions.css"/>-->
            </stylesheets>

            <VBox>

                <MenuBar fx:id="menuBar" VBox.vgrow="NEVER">
                    <Menu mnemonicParsing="false" text="File">
                        <MenuItem mnemonicParsing="false" onAction="#handleExit" text="Exit"/>
                    </Menu>
                    <Menu mnemonicParsing="false" text="Help">
                        <MenuItem fx:id="helpMenuItem" mnemonicParsing="false" onAction="#handleHelp" text="Help"/>
                    </Menu>
                </MenuBar>

                <HBox VBox.vgrow="ALWAYS" styleClass="main">

                    <StackPane fx:id="helpDeskWindowPlaceholder" minWidth="200" maxWidth="200"  VBox.vgrow="ALWAYS">
                    </StackPane>

                    <VBox id="parentVBox" HBox.hgrow="ALWAYS">

                        <TabPane fx:id="tabPanePlaceHolder"
                                 VBox.vgrow="ALWAYS"
                                 tabClosingPolicy="UNAVAILABLE"
                                 stylesheets="@cssfiles/CustomTabPane.css">

                            <Tab text="Planner">
                                <StackPane fx:id="plannerContentPlaceholder" VBox.vgrow="ALWAYS"/>
                            </Tab>
                            <Tab text="Finances">
                                <StackPane fx:id="financeContentPlaceholder" VBox.vgrow="ALWAYS"/>
                            </Tab>
                            <Tab text="Ccas">
                                <StackPane fx:id="ccaContentPlaceholder" VBox.vgrow="ALWAYS"/>
                            </Tab>
                            <Tab text="Courses">
                                <StackPane fx:id="moduleContentPlaceholder" VBox.vgrow="ALWAYS"/>
                            </Tab>

                        </TabPane>

                        <StackPane VBox.vgrow="NEVER" fx:id="resultDisplayPlaceholder" styleClass="pane-with-border"
                                   minHeight="100" prefHeight="100" maxHeight="100">
                            <padding>
                                <Insets top="5" right="10" bottom="5" left="10"/>
                            </padding>
                        </StackPane>

                        <StackPane VBox.vgrow="NEVER" fx:id="commandBoxPlaceholder" styleClass="pane-with-border">
                            <padding>
                                <Insets top="5" right="10" bottom="5" left="10"/>
                            </padding>
                        </StackPane>
                        <StackPane fx:id="statusbarPlaceholder" VBox.vgrow="NEVER"/>
                    </VBox>

                </HBox>
            </VBox>
        </Scene>
    </scene>
</fx:root>