* {
  box-sizing: border-box;
  font-family: 'Poppins', sans-serif;
}

body {
  background: linear-gradient(135deg, #4facfe, #00f2fe);
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
  margin: 0;
}

.calculator {
  background: #fff;
  border-radius: 15px;
  box-shadow: 0 5px 15px rgba(0,0,0,0.2);
  width: 280px;
  padding: 20px;
}

#display {
  width: 100%;
  height: 50px;
  border: none;
  outline: none;
  text-align: right;
  font-size: 24px;
  margin-bottom: 15px;
  padding-right: 10px;
  border-radius: 8px;
  background: #f1f1f1;
}

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

.btn {
  padding: 15px;
  font-size: 18px;
  border: none;
  border-radius: 8px;
  background: #e0e0e0;
  cursor: pointer;
  transition: background 0.2s;
}

.btn:hover {
  background: #d4d4d4;
}

.equal {
  grid-column: span 2;
  background: #4facfe;
  color: white;
  font-weight: bold;
}

.equal:hover {
  background: #00c3ff;
}