html, body {
  margin: 0;
  padding: 0;
  height: 100%;
  width: 100%;
  background: #220824;
  overflow: hidden;
}

/* Container fills viewport */
.container {
  height: 100dvh; /* dynamic viewport height (mobile-safe) */
  width: 100vw;

  display: flex;
  align-items: center;      /* vertical centering */
  justify-content: center;  /* horizontal centering */
}

/* Picture behaves like a wrapper */
picture {
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
}

/* THIS is the key */
img {
  height: 100%;   /* fill vertical space */
  width: auto;    /* maintain aspect ratio */
  display: block;
}