.lightbox {
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,.85);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 9999;
}

.lightbox img {
  max-width: 90%;
  max-height: 90%;
}

.lightbox .prev,
.lightbox .next {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
  font-size: 3rem;
  color: #fff;
  cursor: pointer;
  user-select: none;
}

.lightbox .prev { left: 30px; }
.lightbox .next { right: 30px; }