* {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
    }

    body {
      font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
      background-color: #f4f6f8;
      min-height: 100vh;
      color: #333;
      line-height: 1.6;
      padding: 2rem;
    }

    .container {
      max-width: 800px;
      margin: 0 auto;
    }

    .header {
      text-align: center;
      margin-bottom: 3rem;
    }

    .page-title {
      font-size: 2.5rem;
      font-weight: 700;
      background: linear-gradient(45deg, #0066cc, #004a99);
      -webkit-background-clip: text;
      -webkit-text-fill-color: transparent;
      background-clip: text;
      margin-bottom: 0.5rem;
    }

    .page-subtitle {
      color: #666;
      font-size: 1.1rem;
      font-style: italic;
    }

    .top-bar {
      position: fixed;
      top: 2rem;
      left: 2rem;
      z-index: 100;
    }

    .top-bar .btn {
      background: rgba(255, 255, 255, 0.95);
      backdrop-filter: blur(10px);
      color: #0066cc;
      border: 2px solid rgba(0, 102, 204, 0.3);
      padding: 0.75rem 1.5rem;
      border-radius: 50px;
      font-weight: 600;
      text-decoration: none;
      display: inline-flex;
      align-items: center;
      gap: 0.5rem;
      transition: all 0.3s ease;
      box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
    }

    .top-bar .btn:hover {
      background: rgba(0, 102, 204, 0.1);
      border-color: #0066cc;
      transform: translateY(-2px);
      box-shadow: 0 8px 25px rgba(0, 0, 0, 0.15);
    }

    .config-box, .card, .controls {
      background: rgba(255, 255, 255, 0.95);
      backdrop-filter: blur(10px);
      border-radius: 20px;
      padding: 2rem;
      box-shadow: 0 20px 40px rgba(0, 0, 0, 0.1);
      border: 1px solid rgba(255, 255, 255, 0.2);
      margin-bottom: 2rem;
      transition: all 0.3s ease;
    }

    .config-box {
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 1.5rem;
      text-align: center;
    }

    .config-box h3 {
      font-size: 1.5rem;
      font-weight: 700;
      color: #0066cc;
      margin-bottom: 0.5rem;
    }

    .config-controls {
      display: flex;
      align-items: center;
      gap: 1rem;
      flex-wrap: wrap;
      justify-content: center;
    }

    .config-controls label {
      font-weight: 600;
      color: #333;
    }

    .config-controls input {
      padding: 0.5rem 1rem;
      border: 2px solid rgba(0, 0, 0, 0.1);
      border-radius: 10px;
      font-size: 1rem;
      width: 80px;
      text-align: center;
      transition: border-color 0.3s ease;
    }

    .config-controls input:focus {
      outline: none;
      border-color: #0066cc;
    }

    .card {
      min-height: 300px;
      cursor: pointer;
      display: flex;
      flex-direction: column;
      justify-content: center;
      position: relative;
      overflow: hidden;
    }

    .card:hover {
      transform: translateY(-2px);
      box-shadow: 0 25px 50px rgba(0, 0, 0, 0.15);
    }

    .card-header {
      display: flex;
      justify-content: between;
      align-items: center;
      margin-bottom: 1.5rem;
      padding-bottom: 1rem;
      border-bottom: 2px solid rgba(0, 102, 204, 0.1);
    }

    .card-type {
      font-size: 1.2rem;
      font-weight: 700;
      color: #0066cc;
      display: flex;
      align-items: center;
      gap: 0.5rem;
    }

    .card-type::before {
      content: '';
      width: 4px;
      height: 20px;
      background: linear-gradient(45deg, #0066cc, #004a99);
      border-radius: 2px;
    }

    .card-progress {
      position: absolute;
      top: 1rem;
      right: 1.5rem;
      background: rgba(102, 126, 234, 0.1);
      color: #0066cc;
      padding: 0.5rem 1rem;
      border-radius: 25px;
      font-size: 0.9rem;
      font-weight: 600;
      border: 1px solid rgba(0, 102, 204, 0.2);
    }

    .card-content {
      font-size: 1.1rem;
      line-height: 1.7;
      color: #555;
      white-space: pre-wrap;
      flex-grow: 1;
    }

    .card-hint {
      position: absolute;
      bottom: 1.5rem;
      left: 50%;
      transform: translateX(-50%);
      background: rgba(0, 102, 204, 0.9);
      color: white;
      padding: 0.5rem 1rem;
      border-radius: 25px;
      font-size: 0.9rem;
      opacity: 0.8;
      animation: pulse 2s infinite;
    }

    @keyframes pulse {
      0%, 100% { opacity: 0.8; }
      50% { opacity: 1; }
    }

    .controls {
      display: flex;
      gap: 1rem;
      justify-content: center;
      flex-wrap: wrap;
    }

    .btn {
      padding: 0.75rem 2rem;
      border: none;
      border-radius: 50px;
      font-weight: 600;
      cursor: pointer;
      transition: all 0.3s ease;
      font-size: 1rem;
      font-family: inherit;
      text-decoration: none;
      display: inline-flex;
      align-items: center;
      gap: 0.5rem;
      min-width: 120px;
      justify-content: center;
    }

    .btn-primary {
      background: linear-gradient(45deg, #0066cc, #004a99);
      color: white;
      box-shadow: 0 5px 15px rgba(0, 102, 204, 0.4);
    }

    .btn-primary:hover {
      transform: translateY(-2px);
      box-shadow: 0 8px 25px rgba(0, 102, 204, 0.6);
    }

    .btn-secondary {
      background: rgba(255, 255, 255, 0.9);
      color: #0066cc;
      border: 2px solid rgba(0, 102, 204, 0.3);
    }

    .btn-secondary:hover {
      background: rgba(0, 102, 204, 0.1);
      border-color: #0066cc;
    }

    .btn-success {
      background: linear-gradient(45deg, #4CAF50, #45a049);
      color: white;
    }

    .btn-warning {
      background: linear-gradient(45deg, #ff9800, #f57c00);
      color: white;
    }

    .btn-danger {
      background: linear-gradient(45deg, #f44336, #da190b);
      color: white;
    }

    .btn-easy {
      background: linear-gradient(45deg, #2196F3, #1976D2);
      color: white;
    }

    .rating-controls {
      display: grid;
      grid-template-columns: repeat(4, 1fr);
      gap: 1rem;
      margin-bottom: 2rem;
    }

    .completion-card {
      text-align: center;
      padding: 3rem 2rem;
    }

    .completion-icon {
      font-size: 4rem;
      margin-bottom: 1rem;
    }

    .completion-title {
      font-size: 2rem;
      font-weight: 700;
      color: #4CAF50;
      margin-bottom: 1rem;
    }

    .completion-stats {
      background: rgba(76, 175, 80, 0.1);
      padding: 1rem;
      border-radius: 10px;
      margin: 2rem 0;
      color: #4CAF50;
      font-weight: 600;
    }

    .completion-actions {
      display: flex;
      gap: 1rem;
      justify-content: center;
      flex-wrap: wrap;
    }

    .loading-indicator {
      text-align: center;
      padding: 2rem;
      color: #666;
    }

    .loading-spinner {
      display: inline-block;
      width: 40px;
      height: 40px;
      border: 4px solid rgba(0, 102, 204, 0.2);
      border-radius: 50%;
      border-top-color: #0066cc;
      animation: spin 1s ease-in-out infinite;
      margin-bottom: 1rem;
    }

    @keyframes spin {
      to { transform: rotate(360deg); }
    }

    .due-cards-info {
      background: rgba(102, 126, 234, 0.1);
      color: #0066cc;
      padding: 1rem 1.5rem;
      border-radius: 10px;
      margin-bottom: 1.5rem;
      text-align: center;
      font-weight: 600;
      border: 1px solid rgba(0, 102, 204, 0.2);
    }

    /* MathJax styling */
    .MathJax {
      font-size: 1.1em !important;
    }

    /* Code blocks */
    code {
      background: rgba(0, 102, 204, 0.1);
      padding: 0.2rem 0.4rem;
      border-radius: 4px;
      font-family: 'Monaco', 'Menlo', monospace;
      font-size: 0.9em;
    }

    /* Responsive design */
    @media (max-width: 768px) {
      body {
        padding: 1rem;
      }

      .top-bar {
        position: static;
        margin-bottom: 2rem;
        text-align: center;
      }

      .page-title {
        font-size: 2rem;
      }

      .config-controls {
        flex-direction: column;
        align-items: stretch;
      }

      .rating-controls {
        grid-template-columns: repeat(2, 1fr);
      }

      .controls {
        flex-direction: column;
      }

      .completion-actions {
        flex-direction: column;
        align-items: center;
      }

      .btn {
        width: 100%;
        max-width: 300px;
      }

      .card {
        min-height: 250px;
        padding: 1.5rem;
      }

      .card-progress {
        position: static;
        margin-bottom: 1rem;
        align-self: flex-start;
      }
    }

    /* Animations */
    .card, .config-box, .controls {
      animation: slideUp 0.6s ease-out;
    }

    @keyframes slideUp {
      from {
        opacity: 0;
        transform: translateY(30px);
      }
      to {
        opacity: 1;
        transform: translateY(0);
      }
    }