html {
  height: 100%;
}

body {
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100%;
  background-image: url(/pics/seahorse-modified.jpg);
}

a {
  font-size: 8em;
  color: red;
  background-color: black;
  padding: .1em;
}