body {
  font-family: monospace, Arial, Helvetica, sans-serif;
}

main {
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
}

input {
  display: block;
  border: 3px solid #000;
  padding: 6px;
  font-size: 20px;
  text-align: center;
}

button {
  display: block;
  margin-top: 4px;
  width: 100%;
  font-size: 18px;
}

.response {
  line-height: 30px;
}