/* CSS-only noise using SVG filter (no external image needed, very performant) */
#noise-overlay {
  position: fixed;
  inset: 0;
  z-index: 9999;
  pointer-events: none;
  opacity: 0.06;
  mix-blend-mode: overlay;
}

#noise-overlay::before {
  content: '';
  position: absolute;
  inset: -50%;
  width: 200%;
  height: 200%;
  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 256 256' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='4' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)'/%3E%3C/svg%3E");
  background-size: 256px 256px;
  animation: grainShift 0.5s steps(4) infinite;
}

@keyframes grainShift {
  0%   { transform: translate(0, 0); }
  25%  { transform: translate(-64px, -32px); }
  50%  { transform: translate(32px, -64px); }
  75%  { transform: translate(-32px, 64px); }
  100% { transform: translate(64px, 32px); }
}