body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: #f4f4f4;
  font-family: Arial, sans-serif;
}

.calculator {
  background: #c4c8c6;
  padding: 20px;
  border-radius: 12px;
  width: 260px;
  box-shadow: 0 6px 15px rgba(0, 0, 0, 0.15);
}

#display {
  width: 100%;
  height: 50px;
  border: none;
  border-radius: 8px;
  font-size: 20px;
  text-align: right;
  padding-right: 10px;
  margin-bottom: 15px;
  background: #ffffff;
}

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

button {
  height: 50px;
  border: none;
  border-radius: 8px;
  font-size: 18px;
  background: #ffffff;
  cursor: pointer;
}

button:hover {
  background: #ececec;
}

.zero {
  grid-column: span 2;
}