protected JPanel buildMainPanel() {
		JPanel mainPanel = new JPanel(new PairLayout(5, 5));
		mainPanel.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));

		label = new GDLabel("Label: ");
		myChoice = new GhidraComboBox<>();
		myChoice.setName("MYCHOICE");
		myChoice.setEditable(true);
		myChoice.addActionListener(ev -> okCallback());
		myChoice.getAccessibleContext().setAccessibleName("My Choice");
		mainPanel.add(label);
		mainPanel.add(myChoice);
		mainPanel.getAccessibleContext().setAccessibleName("Operand Label");
		return mainPanel;
	}
Define the Main panel for the dialog here.
@return JPanel the completed Main Panel
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/label/OperandLabelDialog.java