html, body { margin: 0; height: 100%; }
body {
  background: #14254F radial-gradient(ellipse at 50% 45%, #1d3366 0, #14254F 55%, #0f1c3d 100%) fixed;
  display: grid;
  place-items: center;
}
h1 { margin: 0; padding: 0 16px; }
h1 img { display: block; width: min(620px, 84vw); height: auto; }