html, body {
    -webkit-touch-callout: none;
    -webkit-user-select: none;
    -khtml-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    user-select: none;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-direction: column;
    height: 100%;
    font: 100%;
}

div {
  font-size: 10em;
}

button {
  font-size: 1.5em;
  padding: 0.8em;
}

.negative {
  color: red;
}

.positive {
  color: black;
}

@media only screen and (max-width: 600px) {
  div {
    font-size: 6em;
  }
}