Main.java

import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.control.PasswordField;
import javafx.scene.control.Button;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class Main extends Application {
    @Override
    public void start(Stage stage) {

        Label titleLabel = new Label("login");

        TextField usernameField = new TextField();

        //USER NAME LABEL
        usernameField.setPromptText("Username");
        usernameField.setMaxWidth(280);

        PasswordField passwordField = new PasswordField();

        //PASSWORD LABEL
        passwordField.setPromptText("Password");
        passwordField.setMaxWidth(280);

        Button loginButton = new Button("Login");

        //LoginButton On Action
        loginButton.setOnAction(e -> {
            if (usernameField.getText().equals("yassine") && passwordField.getText().equals("123")) {
                System.out.println("Login successful !");
            } else {
                System.out.println("Wrong credentials try again ");
            }
        });

        VBox root = new VBox(10);// 10px margin

        //Root plays div role simple as that
        root.getChildren().addAll(titleLabel,usernameField,passwordField,loginButton);
        root.setStyle("-fx-alignment: center ;");// using css to center everything
        VBox.setMargin(titleLabel, new Insets(0,0,0,0));

        Scene scene = new Scene(root , 350 , 600);

        scene.getStylesheets().add(getClass().getResource("styles/MainStyle.css").toExternalForm());

        stage.setTitle("LinkedClone App");
        stage.setScene(scene);
        stage.setResizable(false);
        stage.show();
    }

    public  static void main(String[] args) {
        launch();
    }

}