JDialog dialog = new JDialog();
Container container = dialog.getContentPane();

JPanel serverPanel = new JPanel();
JLabel serverLabel = new JLabel("Server ip: ");
serverLabel.setForeground(Color.green);
JTextField serverInput = new JTextField(20);
serverInput.setBackground(Color.black);
serverInput.setForeground(Color.white);
serverInput.setBorder(BorderFactory.createLineBorder(Color.green, 2));
serverPanel.add(serverLabel);
serverPanel.add(serverInput);

JPanel namePanel = new JPanel();
JLabel nameLabel = new JLabel("Ваш ник: ");
nameLabel.setForeground(Color.green);
JTextField nameInput = new JTextField(20);
nameInput.setBackground(Color.black);
nameInput.setForeground(Color.white);
nameInput.setBorder(BorderFactory.createLineBorder(Color.green, 2));
namePanel.add(nameLabel);
namePanel.add(nameInput);

JPanel authPanel = new JPanel();
JButton authBtn = new JButton("Авторизироваться");
authBtn.setForeground(Color.green);
authBtn.setBackground(Color.black);
authBtn.setBorder(BorderFactory.createCompoundBorder(
    BorderFactory.createLineBorder(Color.green, 2),
    BorderFactory.createEmptyBorder(10, 10, 10, 10)
));
authPanel.add(authBtn);

container.setLayout(new BoxLayout(container, BoxLayout.Y_AXIS));
container.add(serverPanel);
container.add(namePanel);
container.add(authPanel);

dialog.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
dialog.setLocationRelativeTo(null);
dialog.pack();
container.setBackground(Color.black);
dialog.setVisible(true);