Swirl

@grid: 1 / 100vw 100vh;

@content: @pattern(
  r: length(pos);
  a: atan(pos.y, pos.x) + 3 / (r + .2) + .4t;
  g: smoothstep(.3, .55, fract(2a / π + 9r - .5t));
  c: hsl(.55 + .25sin(4r - .2t), .8, mix(.06, .92, g));
  c: mix(c, #9be8ff, .35exp(-2.2r));
  fill: c * (1 - .65smoothstep(.4, .75, r));
);