body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: linear-gradient(135deg, #1c5066, #203a43, #69b3d5);
  font-family: Arial, sans-serif;
}

.calculator {
  background: #1e272e;
  border-radius: 20px;
  box-shadow: 0 10px 25px rgba(0,0,0,0.4);
  padding: 20px;
  width: 320px;
}

.display {
  width: 100%;
  height: 60px;
  font-size: 24px;
  text-align: right;
  padding: 10px;
  margin-bottom: 15px;
  border: none;
  border-radius: 10px;
  background: #dfe6e9;
}

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

.btn {
  height: 60px;
  border: none;
  border-radius: 12px;
  font-size: 20px;
  cursor: pointer;
  transition: background 0.2s;
}

.btn.number {
  background: #0984e3;
  color: white;
}

.btn.operator {
  background: #6c5ce7;
  color: white;
}

.btn.function {
  background: #00b894;
  color: white;
}

.btn.equals {
  background: #d63031;
  color: white;
  grid-column: span 1;
}

.btn:hover {
  opacity: 0.8;
}