* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: 'Segoe UI', sans-serif;
  background-color: #f0f0f0;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
}

.calculator {
  background-color: #1e1e1e;
  border-radius: 12px;
  padding: 20px;
  width: 300px;
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.3);
}

#display {
  width: 100%;
  height: 60px;
  background-color: #333;
  color: white;
  border: none;
  border-radius: 8px;
  font-size: 2rem;
  text-align: right;
  padding: 0 15px;
  margin-bottom: 15px;
  outline: none;
}

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

button {
  border: none;
  border-radius: 8px;
  font-size: 1.2rem;
  cursor: pointer;
  background-color: #505050;
  color: white;
  padding: 15px;
  transition: background-color 0.2s;
}

button:hover {
  background-color: #666;
}

button:active {
  background-color: #444;
}

.equals {
  background-color: #ff9500;
}

.equals:hover {
  background-color: #ffaa33;
}

.zero {
  grid-column: span 2;
}

.operator {
  background-color: #ff9500;
}

.operator:hover {
  background-color: #ffaa33;
}