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

.calculator {
  background: #fff;
  border-radius: 10px;
  box-shadow: 0 10px 20px rgba(0, 0, 0, 0.2);
  padding: 20px;
}

.display {
  background: #222;
  color: #fff;
  font-size: 2em;
  padding: 10px;
  border-radius: 5px;
  text-align: right;
  margin-bottom: 20px;
}

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

.btn {
  background: #00bcd4;
  color: #fff;
  border: none;
  border-radius: 5px;
  font-size: 1.5em;
  padding: 20px;
  cursor: pointer;
  transition: background 0.3s ease;
}

.btn:hover {
  background: #0097a7;
}

.btn:active {
  background: #00796b;
}