body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  margin: 0;
  font-family: Arial, sans-serif;
  background: #f4f4f4;
}
.calculator {
  background: #fff;
  padding: 1rem;
  border-radius: 8px;
  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
  max-width: 400px;
  width: 100%;
}
.display {
  width: 100%;
  height: 3rem;
  text-align: right;
  font-size: 1.5rem;
  padding: 0.5rem;
  margin-bottom: 0.5rem;
  border: 1px solid #ccc;
  border-radius: 4px;
}
.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.5rem;
}
.buttons button {
  padding: 1rem;
  font-size: 1.25rem;
  border: none;
  border-radius: 4px;
  background: #e0e0e0;
  cursor: pointer;
}
.buttons button:hover {
  background: #d5d5d5;
}
.buttons .clear {
  grid-column: span 4;
  background: #ff6666;
  color: #fff;
}
.buttons .clear:hover {
  background: #ff4d4d;
}