  const canvas = document.getElementById("canvas");
      // to test pow2 resizing
      canvas.height = 1000; canvas.width = 1000;
      const ctx = canvas.getContext("2d");
      ctx.font = "Bold " + canvas.width / 12 + "px 'Helvetica'";
      ctx.textAlign = "center";
      ctx.textBaseline = "top";

      const update = dt => {
        ctx.clearRect(0, 0, canvas.width, canvas.height);
        ctx.save();
        ctx.fillStyle = `hsl(${((dt / 20) % 360).toFixed(2)}, 100%, 50%)`;
        ctx.fillRect(0, 0