Customise JOptionPane

[Lakshmi Anantharaman]

I ned a confirm optionpane with white backgraoud ,black text with Monospaced font . But my attempts to customize the option pane never goes through .
Why ?
Is there a way I can achieve this ?
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My code
public int onWindowClose(){
message="Do you want to Exit Dictionary Admin ?";
messageType=JOptionPane.QUESTION_MESSAGE;
optionType=JOptionPane.YES_NO_OPTION;
title = " Test ";
Object [] options ={"Yes" ,"No" };
Object initialValue = "Yes";
Icon icon = null;
chosen = getOptionPane().showConfirmDialog(mainFrame, message, title,optionType,messageType, icon);
return chosen;
}
private JOptionPane getOptionPane(){
JOptionPane optionPane = new JOptionPane();
optionPane.setBackground(Color.white);
optionPane.setForeground(Color.black);
optionPane.setFont(new Font("Monospaced", Font.PLAIN,10));
return optionPane;

}