body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  margin: 0;
  background-color: #f0f0f0;
}

.calculator {
  border: 1px solid #ccc;
  border-radius: 5px;
  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.1);
  width: 300px;
}

.display {
  background-color: #222;
  color: white;
  text-align: right;
  padding: 20px;
  font-size: 2em;
}

.display input {
  width: 100%;
  border: none;
  background-color: #222;
  color: white;
  text-align: right;
  font-size: 1em;
}

.keys {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
}

button {
  border: 1px solid #ccc;
  padding: 20px;
  font-size: 1.5em;
  cursor: pointer;
}

button:hover {
  background-color: #ddd;
}

.operator {
  background-color: #f0ad4e;
  color: white;
}

.operator:hover {
  background-color: #ec971f;
}