* { box-sizing: border-box; }
html, body { margin: 0; min-height: 100%; }
body { background: #000; }
.site {
  width: 100%;
  min-height: 100vh;
  min-height: 100dvh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #000;
}
.site img {
  display: block;
  width: min(90vw, 88vh, 640px);
  width: min(90vw, 88dvh, 640px);
  height: auto;
  object-fit: contain;
}