body {
      background: linear-gradient(135deg, #6a11cb 0%, #2575fc 100%);
      min-height: 100vh;
      display: flex;
      align-items: center;
      padding: 20px 0;
    }
    .calculator-card {
      background: rgba(255, 255, 255, 0.92);
      border-radius: 20px;
      box-shadow: 0 10px 30px rgba(0, 0, 0, 0.2);
      overflow: hidden;
      max-width: 500px;
      margin: 0 auto;
    }
    .card-header {
      background: linear-gradient(to right, #3498db, #2c3e50);
      color: white;
      padding: 25px 20px;
      text-align: center;
    }
    .card-body {
      padding: 30px;
    }
    .btn-operation {
      background: linear-gradient(to right, #3498db, #2c3e50);
      border: none;
      transition: all 0.3s;
      font-weight: 600;
      margin: 5px;
      color: white;
    }
    .btn-operation:hover {
      transform: translateY(-2px);
      box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
      color: white;
    }
    .result-box {
      background-color: #f8f9fa;
      border-radius: 5px;
      padding: 15px;
      margin-top: 20px;
      border-left: 4px solid #3498db;
      font-weight: bold;
      text-align: center;
      font-size: 1.2rem;
    }
    .bi-calculator {
      font-size: 1.8rem;
      margin-bottom: 10px;
      color: #3498db;
    }
    .operations-grid {
      display: grid;
      grid-template-columns: repeat(2, 1fr);
      gap: 10px;
      margin-top: 20px;
    }