Run the code from an attached project.

There are 2 interesting places:

first:
        //You can comment out these lines.
        Font.loadFont(JavaApplication8.class.getResourceAsStream("arialw7.ttf"), 40);
        String cssFontUrl = JavaApplication8.class.getResource("custom_font.css").toExternalForm();
        scene.getStylesheets().add(cssFontUrl);
        
second:
        b.setFont(new Font(20));

When I have the first, the second doesn't affect.
comment out the first, the second will start working.