how to make an existing JButton (from palette) into a custom one?

i'm making a simple calculator application using intellij. i've got it to work well, now i'm trying to customise it in order for it to look aesthetically pleasing.

the problem is that i've made the entire gui using intellij's gui designer. for example, the current JButton colour is a default blue-ish gradient, and i've been trying to change it to a green gradient.

using the gui designer, i changed the colour but it becomes flat coloured rather than a gradient. i searched online to see whether there was something i could do but most sites require me to have coded a custom button manually, which i haven't done.

could someone please guide me through how i can change my existing button to one that can be more customised?

https://i.sstatic.net/fhWWoR6t.jpg

To apply a custom gradient to your button, you can override the paintComponent(...) method and disable the default fill like this:

import javax.swing.*;
import java.awt.*;

public class GradientButton extends JButton {

    public GradientButton(String text) {
        super(text);
        setContentAreaFilled(false);
    }

    @Override
    protected void paintComponent(Graphics g) {
        Graphics2D g2 = (Graphics2D) g.create();
        int width = getWidth();
        int height = getHeight();

        GradientPaint gradient = new GradientPaint(
                0, 0, new Color(0x6DD5FA),
                0, height, new Color(0x2980B9)
        );
        g2.setPaint(gradient);
        g2.fillRect(0, 0, width, height);
        g2.dispose();

        super.paintComponent(g);
    }
}

Then, in the IntelliJ GUI Designer you can create this GradientButton class and select your button, then enable "Custom Create", and use:

new GradientButton("My Button");

This way you can still use the GUI designer but customize specific components with your own rendering.