/* --- Global Styles --- */
    body {
      font-family: 'Vazirmatn', sans-serif;
      background-color: #f4f7f6; /* Soft, professional background */
      color: #333;
      line-height: 1.6;
    }
    .container {
      max-width: 960px; /* Standard professional width */
    }

    /* --- Header & Footer --- */
    .site-header {
      background-color: #ffffff;
      box-shadow: 0 2px 5px rgba(0, 0, 0, 0.05);
      padding: 1rem 0;
    }
    .site-header .nav-link {
      color: #555;
      font-weight: 500;
      transition: color 0.3s ease;
    }
    .site-header .nav-link:hover {
      color: #28a745; /* Green accent */
    }
    .site-footer {
      background-color: #343a40; /* Dark footer */
      color: #f8f9fa;
      padding: 2rem 0;
      font-size: 0.9rem;
    }
    .site-footer p {
      margin-bottom: 0.5rem;
    }

    /* --- Main Content Card --- */
    .content-card {
      border: none;
      border-radius: 12px;
      box-shadow: 0 4px 12px rgba(0, 0, 0, 0.05);
      transition: transform 0.2s ease-in-out, box-shadow 0.2s ease-in-out;
    }
    .content-card:hover {
      transform: translateY(-5px);
      box-shadow: 0 8px 18px rgba(0, 0, 0, 0.1);
    }
    .card-header-custom {
      background-color: #e9ecef;
      border-bottom: 1px solid #dee2e6;
      padding: 1.5rem;
      border-top-left-radius: 12px;
      border-top-right-radius: 12px;
    }
    .card-body-custom {
      padding: 2rem;
    }

    /* --- Headings & Titles --- */
    h1, h2, h3, h4, h5, h6 {
      font-weight: 700;
      color: #28a745; /* Primary green */
    }
    .section-title {
      font-size: 1.75rem;
      margin-bottom: 1rem;
      color: #218838; /* Darker green */
    }
    .subsection-title {
      font-size: 1.25rem;
      color: #343a40;
      margin-bottom: 1.5rem;
      border-bottom: 2px solid #28a745;
      padding-bottom: 0.5rem;
    }

    /* --- Navigation Tabs --- */
    .nav-tabs-custom .nav-link {
      border: none;
      padding: 15px 25px;
      font-weight: 600;
      color: #555;
      transition: color 0.3s ease, border-bottom 0.3s ease;
      border-bottom: 3px solid transparent;
    }
    .nav-tabs-custom .nav-link:hover {
      color: #28a745;
    }
    .nav-tabs-custom .nav-link.active {
      color: #218838; /* Darker green for active */
      border-bottom: 3px solid #28a745;
    }

    /* --- Form Elements --- */
    .form-label {
      font-weight: 600;
      color: #444;
      margin-bottom: 10px;
    }
    .form-control, .form-select {
      border-radius: 8px;
      padding: 12px 15px;
      font-size: 1rem;
      border: 1px solid #ced4da;
      transition: border-color 0.3s ease, box-shadow 0.3s ease;
    }
    .form-control:focus, .form-select:focus {
      border-color: #80bdff; /* Bootstrap focus blue */
      box-shadow: 0 0 0 0.25rem rgba(40, 167, 69, 0.25); /* Focus shadow with green */
    }
    .input-group-text {
      background-color: #e9ecef;
      border-color: #ced4da;
      border-radius: 8px;
      font-size: 0.95rem;
      font-weight: 500;
    }
    .form-text {
      font-size: 0.85rem;
      color: #6c757d;
      margin-top: 8px;
    }

    /* --- Result Display Box --- */
    .result-display {
      background-color: #ffffff; /* White background for results */
      border: 1px solid #dee2e6;
      border-radius: 10px;
      padding: 20px;
      margin-top: 15px;
      min-height: 180px; /* Adjusted height */
      display: flex;
      flex-direction: column;
      justify-content: center;
      transition: box-shadow 0.3s ease;
    }
    .result-display:hover {
       box-shadow: 0 2px 8px rgba(0, 0, 0, 0.08);
    }
    .result-placeholder {
      display: flex;
      justify-content: center;
      align-items: center;
      height: 100%;
      color: #adb5bd;
      font-size: 1.1rem;
      text-align: center;
    }
    .result-item {
      margin-bottom: 1.5rem;
      transition: opacity 0.3s ease;
    }
     .result-item:last-child {
       margin-bottom: 0;
     }
    .result-label {
      font-size: 0.9rem;
      color: #495057;
      font-weight: 600;
      margin-bottom: 8px;
      text-transform: uppercase; /* Uppercase labels */
      letter-spacing: 0.5px;
    }
    .result-value {
      font-size: 1.6rem; /* Larger value */
      font-weight: 700;
      color: #007bff; /* Primary blue for values */
      display: block; /* Ensure it takes full width */
    }
    .result-unit {
      font-size: 0.95rem;
      color: #6c757d;
      font-weight: 500;
      margin-left: 8px;
    }
    .result-sub-unit {
      font-size: 0.8rem;
      color: #6c757d;
      margin-left: 5px;
      display: block; /* Sub unit on new line */
    }

    /* --- Buttons --- */
    .btn-submit {
      background-color: #28a745; /* Green */
      border-color: #28a745;
      color: white;
      padding: 12px 30px;
      font-weight: 700;
      border-radius: 8px;
      transition: background-color 0.3s ease, border-color 0.3s ease;
      font-size: 1.1rem;
    }
    .btn-submit:hover {
      background-color: #218838;
      border-color: #1e7e34;
    }
    .btn-reset {
      background-color: #6c757d; /* Grey */
      border-color: #6c757d;
      color: white;
      padding: 12px 30px;
      font-weight: 700;
      border-radius: 8px;
      transition: background-color 0.3s ease, border-color 0.3s ease;
      font-size: 1.1rem;
    }
    .btn-reset:hover {
      background-color: #5a6268;
      border-color: #545b62;
    }

    /* --- Responsive adjustments --- */
    @media (max-width: 768px) {
      .content-card {
        margin-bottom: 20px;
      }
      .nav-tabs-custom .nav-link {
        padding: 10px 15px;
        font-size: 0.9rem;
      }
      .result-value {
        font-size: 1.3rem;
      }
      .result-unit {
         font-size: 0.9rem;
      }
    }