const canvas = document.querySelector("#board canvas");
const ctx = canvas.getContext("2d");
const { width: w, height: h } = canvas;
ctx.fillStyle = "black";
ctx.fillRect(0, 0, w, h);
ctx.fillStyle = "#555";

let x, y, radius;

for (let i = 0; i < 550; i++) {
  x = Math.random() * w;
  y = Math.random() * h;
  radius = Math.random() * 3;
  ctx.beginPath();
  ctx.arc(x, y, radius, 0, Math.PI*2, false);
  ctx.fill();
}