* {
  box-sizing: border-box;
}

body {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  margin: 0;
  background: #f4f4f4;
  font-family: Arial, sans-serif;
}

.calculator {
  background: #fff;
  padding: 1rem;
  border-radius: 0.5rem;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
  width: 100%;
  max-width: 400px;
}

#display {
  width: 100%;
  height: 3rem;
  font-size: 1.5rem;
  text-align: right;
  padding: 0.5rem;
  margin-bottom: 1rem;
  border: 1px solid #ccc;
  border-radius: 0.25rem;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.5rem;
}

button {
  padding: 1rem;
  font-size: 1.2rem;
  border: none;
  border-radius: 0.25rem;
  background: #e0e0e0;
  cursor: pointer;
  transition: background 0.2s;
}

button:hover {
  background: #d5d5d5;
}

button:active {
  background: #c0c0c0;
}

[data-action="operator"] {
  background: #ff9500;
  color: #fff;
}

[data-action="operator"]:hover {
  background: #e08e00;
}

[data-action="calculate"] {
  background: #007aff;
  color: #fff;
}

[data-action="calculate"]:hover {
  background: #006ae6;
}

[data-action="clear"] {
  background: #ff3b30;
  color: #fff;
}

[data-action="clear"]:hover {
  background: #e03228;
}