.container {
  width: 100%;
  height: 300px;
}

h1 {
  text-align: center;
  border-bottom: 1px solid #ff0505;
}

#display {
  width: 100%;
  font-size: 72px;
  text-align: center;
  margin: 0px auto;
}

.buttons {
  text-align: center;
}

button {
  color: #fff;
  background: #000;
  border: none;
  width: 60px;
  height: 30px;
}