#cosmic-bg {
  position: fixed;
  inset: 0;
  overflow: hidden;
  z-index: -1;
  background: radial-gradient(circle at top, #0f172a 0, #020617 55%, #000 100%);
}

/* simple layers */
.stars-layer,
.nebula-layer,
.grid-layer {
  position: absolute;
  inset: 0;
  opacity: 0.7;
}