* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: Arial, sans-serif;
}

body {
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  background: #121212;
}

.calculator {
  background: #1f1f1f;
  padding: 20px;
  border-radius: 16px;
  width: 280px;
  box-shadow: 0 15px 40px rgba(0, 0, 0, 0.6);
}

#display {
  width: 100%;
  height: 60px;
  margin-bottom: 15px;
  border: none;
  border-radius: 10px;
  background: #2b2b2b;
  color: #fff;
  font-size: 24px;
  text-align: right;
  padding: 10px;
}

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

button {
  height: 55px;
  border: none;
  border-radius: 12px;
  font-size: 18px;
  cursor: pointer;
  background: #333;
  color: #fff;
  transition: 0.2s;
}

button:hover {
  background: #444;
  transform: translateY(-2px);
}

button:active {
  transform: translateY(0);
}

.zero {
  grid-column: span 2;
}

button:last-child {
  background: #ff9800;
  color: #000;
}

button:last-child:hover {
  background: #ffa726;
}