clock.css

* {
  box-sizing: border-box;
}

html, body {
  height: 100%;
  width: 100%;
  color: white;
}

#clock {
  text-align: center;
  position: relative;
  top: 50%;
  font-family: 'Karla', sans-serif;
  font-size: 4.5rem;
  margin-top: -2.25rem;
}