Here is my simple application:

```
public class MainFrame extends JFrame{
    private Dimension size;
    private JPanel buttonPanel;
    private JButton button;

public MainFrame() throws ClassNotFoundException{
    super("Applikacja1");

    try {
        UIManager.setLookAndFeel("com.formdev.flatlaf.FlatDarkLaf");
    } catch (Exception ex) {

    }
    JFrame.setDefaultLookAndFeelDecorated(true);
    size = new Dimension(350, 530);
    setPreferredSize(size);
    setMinimumSize(size);
    setLocationRelativeTo(null);
    setLayout(new BorderLayout());
    pack();

    //setting button 
    button = new JButton("Start programu");
    button.setVisible(true);
    this.add(button);

    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);
    setResizable(false);
}
}

```

![Sample program](https://i.stack.imgur.com/z91dt.png)

What I need to do in order to change look of this program to FlatLaf and use their libraries?
What i need to download from internet? I tried download whole code(from here <https://www.formdev.com/flatlaf/>) next add it as libraries to netbeans and it didn't work. Can someone do a little totally-newbie tutorial how to do it?