body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: #1e1e2e;
  font-family: Arial, sans-serif;
  margin: 0;
}

.calculator {
  background: #2a2a3b;
  padding: 20px;
  border-radius: 15px;
  box-shadow: 0px 4px 12px rgba(0, 0, 0, 0.5);
  width: 320px;
}

#display {
  width: 100%;
  height: 60px;
  background: #111;
  color: #0f0;
  font-size: 1.5rem;
  text-align: right;
  border: none;
  border-radius: 10px;
  padding: 10px;
  margin-bottom: 15px;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}

button {
  padding: 15px;
  font-size: 1.1rem;
  border: none;
  border-radius: 10px;
  background: #3c3c4d;
  color: white;
  cursor: pointer;
  transition: background 0.2s;
}

button:hover {
  background: #5a5a75;
}