* {
  box-sizing: border-box;
}

body {
  font-family: 'Segoe UI', sans-serif;
  background: #f5f5f5;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  margin: 0;
}

.calculator {
  background: #222;
  border-radius: 12px;
  width: 320px;
  padding: 20px;
  box-shadow: 0 10px 25px rgba(0, 0, 0, 0.3);
}

.display {
  background: #111;
  color: #0f0;
  font-size: 2.2em;
  padding: 20px;
  border-radius: 6px;
  text-align: right;
  margin-bottom: 10px;
  overflow: hidden;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
}

.btn {
  font-size: 1.2em;
  padding: 20px;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  background-color: #333;
  color: white;
  transition: background 0.2s;
}

.btn:hover {
  background-color: #444;
}

.operator {
  background-color: #ff9500;
  color: white;
}

.operator:hover {
  background-color: #e68a00;
}

.equal {
  background-color: #28a745;
  grid-column: span 2;
  color: white;
}

.equal:hover {
  background-color: #218838;
}

.clear {
  background-color: #dc3545;
  grid-column: span 4;
  margin-top: 10px;
}

.clear:hover {
  background-color: #c82333;
}