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

.calculator {
  background: white;
  padding: 20px;
  border-radius: 12px;
  box-shadow: 0px 0px 15px rgba(0,0,0,0.1);
}

#display {
  width: 100%;
  height: 50px;
  font-size: 24px;
  text-align: right;
  padding-right: 10px;
  margin-bottom: 10px;
  border-radius: 5px;
  border: 1px solid #ddd;
}

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

button {
  height: 50px;
  font-size: 18px;
  border: none;
  background: #e0e0e0;
  border-radius: 8px;
  cursor: pointer;
  transition: 0.2s;
}

button:hover {
  background: #ccc;
}