firefly.css

@supports (--firefly: 9) {
  .firefly *,
  .firefly {
    --firefly-hyper: -36deg;
    --firefly-hover: -72deg;
    --firefly-focus: -108deg;
    --firefly-angle: 0deg;
    --firefly-image: none;
    --firefly-glow: #528;
    --firefly-feel: #fa8;
    --firefly-film: hue-rotate(
      var(--firefly-angle)
    );
    color: var(--firefly-glow);
    outline-color: var(--firefly-glow);
    background-color: var(--firefly-feel);
    background-image: var(--firefly-image);
    filter: var(--firefly-film);
  }

  .firefly:any-link,
  .firefly :any-link {
    --firefly-angle: -60deg;
  }

  .firefly:focus,
  .firefly :focus {
    --firefly-angle: -30deg;
  }

  .firefly:any-link:hover,
  .firefly :any-link:hover {
    --firefly-angle: -72deg;
  }
}

/* wait for attr angle support instead of this
[data-firefly=30deg] { --firefly-angle: 30deg }
[data-firefly=36deg] { --firefly-angle: 36deg }
... sparks fly
*/