body {
  margin: 0;
  padding: 0;
  background: #fff;
  font-family: sans-serif;
}

.gallery {
  display: flex;
  flex-direction: column;
  align-items: center;
}

.gallery img {
  width: 100%;
  max-width: 1123px; /* A4横幅(px換算) */
  margin: 40px 0;
  opacity: 0;
  transform: translateY(20px);
  transition: opacity 0.8s ease, transform 0.8s ease;
}

.gallery img.visible {
  opacity: 1;
  transform: translateY(0);
}