body {
  font-family: Arial, sans-serif;
  background: linear-gradient(to right, #4facfe, #00f2fe);
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  margin: 0;
}

.calculator {
  background: #fff;
  padding: 30px;
  border-radius: 12px;
  box-shadow: 0px 4px 20px rgba(0,0,0,0.3);
  text-align: center;
  width: 300px;
}

h1 {
  margin-bottom: 20px;
  color: #333;
}

#display {
  width: 100%;
  height: 50px;
  font-size: 24px;
  text-align: right;
  padding: 5px 10px;
  margin-bottom: 20px;
  border-radius: 6px;
  border: 1px solid #ccc;
}

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

button {
  padding: 15px;
  font-size: 18px;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  background: #4facfe;
  color: white;
  transition: 0.3s;
}

button:hover {
  background: #00c6fb;
}

button.equal {
  grid-row: span 2;
  background: #ff6b6b;
}

button.zero {
  grid-column: span 2;
}