div.luciole {
  position: absolute;
  left:calc(50% - 5px);
  top:calc(50% - 100px);
  width:10px;
  height:10px;
  border-radius: 50%;
  background-color: rgba(255,255,255,0);
  box-shadow: 0 0 12px 6px rgba(255,255,255,0);
  transition: left 0.50s ease, top 0.25s ease;
}