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

.calculator {
  background: #fff;
  padding: 20px;
  border-radius: 10px;
  box-shadow: 0px 5px 20px rgba(0,0,0,0.2);
}

#result {
  width: 100%;
  height: 50px;
  font-size: 2rem;
  text-align: right;
  margin-bottom: 10px;
  padding-right: 10px;
  border: 1px solid #ccc;
  border-radius: 5px;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 70px);
  gap: 10px;
}

button {
  padding: 20px;
  font-size: 1.5rem;
  border: none;
  border-radius: 5px;
  cursor: pointer;
  background: #f0f0f0;
  transition: 0.2s;
}

button:hover {
  background: #ddd;
}

.equal {
  background: #4CAF50;
  color: white;
  grid-row: span 2;
}

.zero {
  grid-column: span 2;
}