* {
  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;
}

.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 {
  font-size: 56px;
  padding: 2.5em;
}