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

.calculator {
  background: white;
  padding: 20px;
  border-radius: 12px;
  box-shadow: 0 0 20px rgba(0, 0, 0, 0.2);
}

#display {
  width: 100%;
  padding: 10px;
  font-size: 1.5em;
  margin-bottom: 10px;
  text-align: right;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 60px);
  gap: 10px;
}

button {
  padding: 15px;
  font-size: 1.2em;
  cursor: pointer;
}