body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: #f0f2f5;
  font-family: Arial, sans-serif;
}

.calculator {
  background: white;
  padding: 20px;
  border-radius: 15px;
  box-shadow: 0px 4px 20px rgba(0,0,0,0.2);
  width: 300px;
}

#result {
  width: 100%;
  height: 50px;
  text-align: right;
  font-size: 1.5rem;
  margin-bottom: 15px;
  padding: 10px;
  border: none;
  border-radius: 10px;
  background: #f9f9f9;
}

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

button {
  padding: 15px;
  font-size: 1.2rem;
  border: none;
  border-radius: 10px;
  cursor: pointer;
  background: #007bff;
  color: white;
  transition: 0.2s;
}

button:hover {
  background: #0056b3;
}