* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  background: #333333;
  color: #efefef;
  font-family: Helvetica Neue;
  line-height: 1.5;
}

.container {
  margin: auto;
  max-width: 768px;
  padding: 20px;
}

.heading {
  padding: 2em;
  text-align: center;
}

.button-container {
  text-align: center;
}

.button {
  background: #486f48;
  border: 2px solid #5d8c56;
  border-radius: 5px;
  color: #efefef;
  cursor: pointer;
  font-size: 24px;
  padding: 10px 20px;
}

.button[disabled] {
  background: transparent;
  border: none;
  opacity: 0.5;
}

#result:not(.empty) {
  background: #666666;
  border-radius: 10px;
  font-size: 56px;
  margin-top: 2em;
  padding: 1em;
}

@media (max-width: 768px) {
  .button {
    font-size: 18px;
    width: 100%;
  }

  .heading {
    padding: 1em;
  }

  #result:not(.empty) {
    font-size: 32px;
    margin-top: 1em;
    padding: 0.5em;
  }
}