body {
  font-family: Arial, sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: #f4f4f9;
}

.calculator {
  background: #fff;
  padding: 15px;
  border-radius: 10px;
  box-shadow: 0 4px 10px rgba(0,0,0,0.1);
}

#display {
  width: 100%;
  height: 50px;
  margin-bottom: 15px;
  text-align: right;
  font-size: 22px;
  padding: 5px;
  border: 1px solid #ccc;
  border-radius: 5px;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 60px);
  gap: 10px;
  justify-content: center;
}

button {
  height: 50px;
  font-size: 18px;
  border: none;
  border-radius: 5px;
  cursor: pointer;
  background: #eee;
  transition: background 0.2s;
}
button:hover {
  background: #ddd;
}
.operator {
  background: #ff9500;
  color: #fff;
}
.equal {
  background: #28a745;
  color: #fff;
  grid-column: span 2;
}
.clear {
  background: red;
  color: #fff;
  grid-column: span 2;
}