How do I set a border around /background image under the minimap? [Phaser Javascript]

I have a minimap on the top right of my screen, and would like to add a border/background under it that way I can see it more clearly! Is there anyway to add an image under the minimap?

Everything I have tried doesn’t stay where it is relative with the window, and just moves with the floor. I have tried using an image, phaser built it graphics, but nothing has seemed to stay with the minimap. I have also tried locking the scroll to (0, 0) but that just ends up making the object on the center of the main camera.

Code:

    this.cameras.main.startFollow(this.player);
    
    //border image here maybe?
    
    this.minimap = this.cameras.add(config.width-210, 10, 200, 200).setZoom(0.1).setName("minimap");
    this.minimap.scrollY = 250;
    this.minimap.scrollX = Phaser.Math.Clamp(this.player.x-100, 800, 2000);
    this.minimap.setBackgroundColor("#000000");
    this.minimap.startFollow(this.player);