.opening {
  position: fixed;
  top: 0;
  left: 0;

  width: 100vw;
  height: 100vh;

  /* iPhone等の動的Viewport対応 */
  height: 100dvh;

  z-index: 99999;

  overflow: hidden;

  background: #c6ff00;

  opacity: 1;
  visibility: visible;

  transition:
    opacity 0.7s ease,
    visibility 0.7s ease;
}

#opening-particles {
  position: absolute;
  inset: 0;

  display: block;

  width: 100%;
  height: 100%;
}

.opening.is-finished {
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
}