#calculator {
  width: 240px;
  margin: 30px auto;
  background: #222;
  border-radius: 10px;
  padding: 10px;
  color: white;
  font-family: sans-serif;
}

#display {
  background: #000;
  color: #0f0;
  text-align: right;
  padding: 15px;
  border-radius: 5px;
  font-size: 24px;
  margin-bottom: 10px;
  overflow-x: auto;
}

#buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 8px;
}

.btn {
  padding: 15px;
  font-size: 18px;
  background: #444;
  border: none;
  border-radius: 5px;
  color: white;
  cursor: pointer;
}

.btn:hover {
  background: #666;
}