Change border of JScrollPane/JScrollBar button

Question

Hi all. I want to change the border height of a JScrollPane/JScrollBar down button.
If you look here
image
you will see that the down button has a two pixel line border at the bottom. I would like that to be only a one pixel line border.
Does anyone know how this can be done?
Thanks...
import javax.swing.*;
public class ScrollPaneTest extends JFrame {
    public ScrollPaneTest() {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        JList list = new JList(new String[] {"bla bla bla","bla bla bla","bla bla bla","bla bla bla","bla bla bla","bla bla bla","bla bla bla","bla bla bla","bla bla bla","bla bla bla"});
        JScrollPane scrollPane = new JScrollPane(list);
        JPanel mainPanel = new JPanel();
        mainPanel.add(scrollPane);
        add(mainPanel);
        pack();
        setLocationRelativeTo(null);
        setVisible(true);
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new ScrollPaneTest();
}

Answer 1

Thanks for the response but that isn't quite what I'm looking for.
I'm happy with the bottom line (border) of the JScrollPane. What I need to get rid of is one pixels worth of border from the bottom of the down button.
Also, it is only for one particular JScrollPane, and not application wide.
Thanks ...