body {
  background-color: black;
}
.clock {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translateX(-50%) translateY(-50%);
  font-size: 7em;
  letter-spacing: 9px;
  color: #39b0ef;
  font-family: "Exo", sans-serif;
  font-weight: 700;
}

@media screen and (max-width: 720px) {
  .clock {
    font-size: 4em;
  }
}