Scrollbar doesn't appear when scrolling - javafx

Question

I'm using HiddenSidesPane to show and hide scrollbar when needed. Scrollbar appears when I move mouse to the edge of the ScrollPane and hides when I move back. However, I have a problem to show scrollbar when the scrolling is detected. You can find my code below:
FXML:
<?import javafx.scene.control.ScrollPane?>
<?import javafx.scene.layout.VBox?>
<?import org.controlsfx.control.HiddenSidesPane?>
<?import java.net.URL?>
<ScrollPane xmlns:fx="http://javafx.com/fxml"
fx:controller="hypermap.components.featurespanel.view.properties.PropertiesTab" fx:id="propertyTabRoot"
fitToWidth="true" hbarPolicy="NEVER" vbarPolicy="NEVER">
<stylesheets>
<URL value="#Scrollbar.css"/>
</stylesheets>
<HiddenSidesPane fx:id="hiddenSidesPane" minWidth="280">
<content>
<VBox fx:id="vboxInsideScroll">
<VBox fx:id="groupsContainer"/>
<VBox fx:id="messageContainer"/>
</VBox>
</content>
</HiddenSidesPane>
</ScrollPane>
CSS file:
.scroll-pane{
-fx-focus-color: none;
-fx-background-color: transparent;
}
.scroll-bar > .increment-button, .decrement-button, .increment-arrow, .decrement-arrow{
-fx-pref-height: 0;
}
.scroll-bar:vertical{
-fx-background-color: transparent;
-fx-border-color: transparent;
-fx-pref-width: 10;
-fx-padding: 0;
}
.scroll-bar:vertical .thumb{
-fx-background-color: color-dark-slate;
-fx-border-radius: 100;
-fx-padding: 0 4 0 0;
-fx-opacity: 0.2
}
.scroll-bar:vertical .track{
-fx-background-color: transparent;
}
Controller file with method using HiddenSidesPane:
#FXML
private VBox groupsContainer;
#FXML
private VBox messageContainer;
#FXML
private ScrollPane propertyTabRoot;
#FXML
private HiddenSidesPane hiddenSidesPane;
private void makeScrollable(ScrollPane scrollPane) {
final Node scrollbar = scrollPane.lookup(".scroll-bar:vertical");
hiddenSidesPane.setRight(scrollbar);
hiddenSidesPane.setTriggerDistance(40);
hiddenSidesPane.setAnimationDuration(Duration.millis(500));
scrollPane.setOnScroll((event -> {
hiddenSidesPane.setRight(scrollbar);
event.consume();
}));
I would be very grateful for any help. Also, I don't know why the scrollbar's thumb has the same hight all the time, even if the content is so huge that it should be smaller.
Thank you!