html,
body {
  height: 100%;
  margin: 0;
}

body {
  display: grid;
  place-items: center;
  background: #111;
  color: #fff;
  font-family: Arial, sans-serif;
  text-align: center;
}

h1 {
  margin: 0 0 1rem;
  font-size: clamp(3rem, 10vw, 7rem);
}

#datum-tijd {
  margin: 0;
  font-size: clamp(1.2rem, 4vw, 2rem);
}