add border-radius:50%; style to this: createRandomPlatform() {
const x = Math.random() * this.canvas.width;
const y = Math.random() * this.canvas.height;
const r = 5 + Math.random() * 10;
this.ctx.beginPath();
this.ctx.arc(x, y, r, 0, 2 * Math.PI);
this.ctx.fill();
this.platforms.push(new Platform(x - r, y - r, 2 * r, 2 * r));
}