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

    html,
    body {
      height: 100%;
    }

    body {
      font-family: 'Inter', sans-serif;
      background: var(--bg-color);
      color: var(--text-color);
      line-height: 1.6;
      transition: background 0.3s, color 0.3s;
    }

    /* Theme Variables */
    :root {
      /* Light Theme */
      --bg-color: #f0f4f8;
      --text-color: #333;
      --container-bg: #ffffff;
      --border-color: #e2e8f0;
      --button-bg: #4F46E5;
      --button-hover: #4338CA;
      --category-header: #4F46E5;
      --output-bg: #F1F5F9;
      --icon-color: #333;
      --card-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
    }

    [data-theme="dark"] {
      --bg-color: #1a202c;
      --text-color: #e2e8f0;
      --container-bg: #2d3748;
      --border-color: #4a5568;
      --button-bg: #667eea;
      --button-hover: #5a67d8;
      --category-header: #667eea;
      --output-bg: #4a5568;
      --icon-color: #e2e8f0;
      --card-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
    }

    /* Layout */
    header {
      text-align: center;
      padding: 2rem 1rem;
      animation: fadeIn 1s ease-out;
    }

    header h1 {
      font-size: 2.5rem;
      font-weight: 600;
    }

    main {
      max-width: 1200px;
      margin: 0 auto;
      padding: 1rem;
    }

    .card {
      background: var(--container-bg);
      border: 1px solid var(--border-color);
      border-radius: 12px;
      padding: 30px;
      box-shadow: var(--card-shadow);
      margin-bottom: 20px;
      animation: slideUp 0.5s ease-out;
    }

    /* Category Cards */
    .categories {
      display: grid;
      grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
      gap: 20px;
      margin: 20px 0;
    }

    .category {
      background: var(--container-bg);
      border: 1px solid var(--border-color);
      border-radius: 10px;
      padding: 15px;
      transition: transform 0.2s ease, box-shadow 0.2s ease;
    }

    .category:hover {
      transform: translateY(-4px);
      box-shadow: 0 8px 16px rgba(0, 0, 0, 0.15);
    }

    .category h3 {
      margin-bottom: 15px;
      font-size: 1.3rem;
      font-weight: 600;
      color: var(--category-header);
      border-bottom: 2px solid var(--category-header);
      padding-bottom: 5px;
    }

    /* Checkbox Group */
    .checkbox-group {
      display: flex;
      flex-direction: column;
      gap: 10px;
    }

    .checkbox-group label {
      display: flex;
      align-items: center;
      gap: 10px;
      font-size: 1.1rem;
      line-height: 1.4;
      cursor: pointer;
      padding: 5px 8px;
      border-radius: 5px;
      transition: background 0.2s ease;
      word-break: break-word;
    }

    .checkbox-group label:hover {
      background: rgba(79, 70, 229, 0.1);
    }

    .checkbox-group input[type="checkbox"] {
      width: 20px;
      height: 20px;
      cursor: pointer;
      margin: 0;
    }

    /* Buttons */
    .btn {
      background: var(--button-bg);
      border: none;
      border-radius: 50px;
      padding: 14px 20px;
      color: #fff;
      font-size: 1.1rem;
      font-weight: 600;
      cursor: pointer;
      width: 100%;
      transition: background 0.3s, transform 0.2s;
      margin-top: 20px;
    }

    .btn:hover {
      background: var(--button-hover);
      transform: scale(1.03);
    }

    .btn:disabled {
      background: #888;
      cursor: not-allowed;
      opacity: 0.6;
    }

    /* Output Area */
    .output {
      background: var(--output-bg);
      border-radius: 10px;
      padding: 20px;
      font-family: monospace;
      white-space: pre-wrap;
      margin-top: 20px;
      font-size: 1.3rem;
    }

    /* Theme Toggle (Top-Right) */
    .theme-toggle {
      position: fixed;
      top: 20px;
      right: 20px;
      width: 50px;
      height: 50px;
      background: var(--button-bg);
      color: var(--icon-color);
      border: none;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 1.5rem;
      cursor: pointer;
      box-shadow: var(--card-shadow);
      transition: background 0.3s, transform 0.2s;
      z-index: 2000;
      /* Ensure it's on top */
    }

    .theme-toggle:hover {
      background: var(--button-hover);
      transform: scale(1.1);
    }

    /* Toast Popup */
    .toast {
      position: fixed;
      bottom: 80px;
      right: 20px;
      background: var(--button-bg);
      color: #fff;
      padding: 12px 24px;
      border-radius: 8px;
      opacity: 0;
      visibility: hidden;
      transition: opacity 0.3s, visibility 0.3s;
      z-index: 1000;
      font-size: 1rem;
    }

    .toast.show {
      opacity: 1;
      visibility: visible;
    }

    /* Animations */
    @keyframes fadeIn {
      from {
        opacity: 0;
      }

      to {
        opacity: 1;
      }
    }

    @keyframes slideUp {
      from {
        transform: translateY(20px);
        opacity: 0;
      }

      to {
        transform: translateY(0);
        opacity: 1;
      }
    }

    /* Responsive Adjustments */
    @media (max-width: 600px) {
      header h1 {
        font-size: 2rem;
      }

      .btn {
        font-size: 1rem;
        padding: 12px 16px;
      }

      .output {
        font-size: 1.1rem;
      }
    }

    /* Footer Styling */
    .app-footer {
      display: flex;
      justify-content: space-between;
      align-items: center;
      background: var(--container-bg);
      border-top: 1px solid var(--border-color);
      padding: 20px 30px;
      border-radius: 12px 12px 0 0;
      box-shadow: 0 -4px 12px rgba(0, 0, 0, 0.05);
      margin-top: 40px;
    }

    .app-footer p {
      margin: 0;
      font-size: 1rem;
      color: var(--text-color);
      font-weight: 500;
    }

    .buy-me-a-coffee a img {
      width: 160px;
      transition: transform 0.2s, box-shadow 0.2s;
      border-radius: 6px;
    }

    .buy-me-a-coffee a img:hover {
      transform: scale(1.05);
      box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
    }