u2-spot {
  position: absolute;
  pointer-events: none;
  z-index: -1;
  background-color: rgba(0,0,0,0.15);
  opacity: 0;
  will-change:transform;
  transition-duration: .3s;
  transition-property: width, height, transform, opacity, border-radius;
  transition-timing-function: ease;
  border-radius: var(--target-border-radius);
  inset: 0;
}

@supports (position-anchor: --test) {
  u2-spot {
    inset: anchor(top) anchor(right) anchor(bottom) anchor(left);
    width: auto;
    height: auto;
    transform: none;
    transition-property: opacity, border-radius, inset;
  }
}