html,
body {
  background-color: rgb(20, 20, 20);
  height: 100vh;
  font-family: sans-serif;
  display: flex;
  flex-direction: column;
  justify-content: center;
  vertical-align: center;
  align-items: center;
}

.button {
  color: white;
  font-size: 2.5rem;
  font-family: sans-serif;
  font-weight: 300;

  height: 17rem;
  width: 17rem;

  border-radius: 50%;
  border: 1px solid #707070;
  background-color: transparent;

  cursor: pointer;
}

.button:hover {
  border-color: #4dbda7;
  transition: 0.4s ease-out;
}

.button span {
  min-width: 2ch;
}

.active {
  border: 7px solid #4dbda7;
  transition: 0.6s ease-out;
}