repositories {
    mavenCentral()
}

dependencies {
    implementation 'org.kordamp.bootstrapfx:bootstrapfx-core:0.4.0'
}

<dependencies>
    <dependency>
        <groupId>org.kordamp.bootstrapfx</groupId>
        <artifactId>bootstrapfx-core</artifactId>
        <version>0.4.0</version>
    </dependency>
</dependencies>

import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;
import org.kordamp.bootstrapfx.BootstrapFX;
import org.kordamp.bootstrapfx.scene.layout.Panel;

public class Sampler extends Application {
    @Override
    public void start(Stage primaryStage) throws Exception {                   //(1)
        Panel panel = new Panel("This is the title");
        panel.getStyleClass().add("panel-primary");                            //(2)
        BorderPane content = new BorderPane();
        content.setPadding(new Insets(20));
        Button button = new Button("Hello BootstrapFX");
        button.getStyleClass().setAll("btn","btn-danger");                     //(2)
        content.setCenter(button);
        panel.setBody(content);

        Scene scene = new Scene(panel);
        scene.getStylesheets().add(BootstrapFX.bootstrapFXStylesheet());       //(3)

        primaryStage.setTitle("BootstrapFX");
        primaryStage.setScene(scene);
        primaryStage.sizeToScene();
        primaryStage.show();
    }
}