body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: linear-gradient(135deg, #667eea, #764ba2);
  font-family: Arial, sans-serif;
}

.calculator {
  background: #1e1e2f;
  padding: 20px;
  border-radius: 15px;
  box-shadow: 0 10px 25px rgba(0,0,0,0.3);
  text-align: center;
}

.calculator h2 {
  color: white;
  margin-bottom: 10px;
}

#display {
  width: 100%;
  height: 60px;
  color: black;
  font-size: 24px;
  margin-bottom: 15px;
  text-align: right;
  padding: 5px;
  border-radius: 10px;
  border: none;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 70px);
  gap: 10px;
}

button {
  height: 60px;
  font-size: 18px;
  border: none;
  border-radius: 10px;
  cursor: pointer;
  background: #2d2d44;
  color: white;
  transition: 0.2s;
}

.green {
  background-color: green;
}

.red {
  background-color: red;
}

button:hover {
  background: #3d3d5c;
}

.equal {
  background: #00c9a7;
}

.equal:hover {
  background: #00a98b;
}

.clear {
  background: #ff4d4d;
}

.zero {
  grid-column: span 2;
}