Can't run the file - Javafx error

Hello. I've created the file and passed the test at task number one, howeover it does not work. When I try to run the file I get error:

Error:(4, 8) java: cannot access javafx.application.Application
  class file for javafx.application.Application not found

My code:

package com.codegym.games.minesweeper;
import com.codegym.engine.cell.*;

public class MinesweeperGame extends Game {
    public static void main(String[] args) {

    }
}

I have compiled many files before and everything was working fine, nonetheless my programs didn't use javafx. Thank you for any help. UPDATE: I have found that JDK 12 doesnt contain JavaFX. So I have downloaded that and added paths and in InteliJ project structure I have added the lib also. Now the file compiles, but there's no window or anything.