html, body {
  margin: 0;
  min-height: 100%;
  background: #111;
}
body {
  padding: 18px;
  box-sizing: border-box;
  font-family: Arial, Helvetica, sans-serif;
}
img.rounded-corners {
  display: block;
  width: 100%;
  max-width: 800px;
  height: auto;
  margin: 0 auto;
  border: 1px solid #444;
  border-radius: 14px;
  box-sizing: border-box;
}