Beesandbombs's spiral animation

@grid: 1x13 / 60vmin / #f5f5f5 @svg(
  viewBox: -5 -5 10 10;
  fill: none;
  stroke-width: .035;
  polygon*13-1 {
    stroke: hsl(@nN(*360), 80%, 50%);
    points: @Plot(
      points: @n2;
      r: $(.7 / cos(@n(*π, /@n2, /2)));
      rotate: @n(*90, /@n2);
    );
  }
);

@size: 2% auto 1;
border-radius: 50%;
background: #000;

offset-path: @shape(
  points: @i2;
  turn: -1;
  r: $(.14 / cos(@i(*π, /@i2, /2)));
  rotate: @i(*90, /@i2);
);

offset-distance: calc(
  60vmin/@I3 + @t(/160%, *@I2(-@i))
);