/* ----- reset & base ----- */
    * { margin: 0; padding: 0; box-sizing: border-box; }
    body {
      font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
      background: #f0f2f5;
      color: #1a2634;
      line-height: 1.6;
    }

    /* ----- primary color ----- */
    :root {
      --primary: #1a4a8a;
      --primary-dark: #2a5a9a;
      --bg-soft: #f8f5f1;
      --border-light: #e2ddd6;
      --sidebar-width: 300px;
    }

    /* ----- header ----- */
    .site-header {
      background: #ffffff;
      border-bottom: 1px solid var(--border-light);
      padding: 0.8rem 2rem;
      position: static;
      top: 0;
      z-index: 100;
      box-shadow: 0 2px 6px rgba(0,0,0,0.02);
    }
    .header-inner {
      max-width: 1400px;
      margin: 0 auto;
      display: flex;
      align-items: center;
      justify-content: space-between;
      flex-wrap: wrap;
      gap: 0.75rem 1rem;
    }
    .logo {
      display: flex;
      align-items: center;
      gap: 0.6rem;
      font-size: 1.5rem;
      font-weight: 700;
      letter-spacing: -0.02em;
      color: #1e1e2a;
      text-decoration: none;
    }
    .logo img {
      width: 38px;
      height: 38px;
      border-radius: 8px;
      object-fit: contain;
    }
    .logo span { color: var(--primary); }
    .nav {
      display: flex;
      align-items: center;
      gap: 1.5rem;
      flex-wrap: wrap;
    }
    .nav a {
      text-decoration: none;
      color: #2c2c3a;
      font-weight: 500;
      font-size: 0.95rem;
      transition: color 0.2s;
    }
    .nav a:hover { color: var(--primary); }
    .nav-button {
      background: var(--primary);
      color: #fff !important;
      padding: 0.5rem 1.4rem;
      border-radius: 40px;
      font-weight: 600;
      font-size: 0.9rem;
      transition: background 0.2s;
    }
    .nav-button:hover { background: var(--primary-dark) !important; }

    /* Mobile hamburger */
    .hamburger {
      display: none;
      background: none;
      border: none;
      font-size: 1.6rem;
      color: #1e1e2a;
      cursor: pointer;
      padding: 0.2rem 0.5rem;
    }
    .hamburger:hover { color: var(--primary); }

    /* ----- layout: article + sidebar (menu) ----- */
    .page-wrapper {
      max-width: 1400px;
      margin: 2rem auto;
      padding: 0 1.5rem;
      display: grid;
      grid-template-columns: 1fr var(--sidebar-width);
      gap: 2.5rem;
      align-items: start;
    }

    /* ----- article ----- */
    .article-wrapper {
      background: #ffffff;
      border-radius: 20px;
      padding: 2rem 2.2rem 2.8rem;
      box-shadow: 0 4px 16px rgba(0,0,0,0.03);
      border: 1px solid var(--border-light);
      min-width: 0;
    }
    .article-header { margin-bottom: 2rem; }
    .breadcrumb {
      font-size: 0.85rem;
      color: #6b6b7a;
      margin-bottom: 1rem;
    }
    .breadcrumb a { color: #6b6b7a; text-decoration: none; }
    .breadcrumb a:hover { color: var(--primary); }
    .breadcrumb span { margin: 0 0.3rem; }

    h1 {
      font-size: 2.2rem;
      font-weight: 700;
      letter-spacing: -0.02em;
      line-height: 1.2;
      margin: 0.5rem 0 0.75rem;
      color: #1e1e2a;
    }
    .article-intro {
      font-size: 1.1rem;
      color: #2f2f3d;
      max-width: 720px;
      margin: 0.5rem 0 1rem;
    }
    .article-meta {
      font-size: 0.9rem;
      color: #6b6b7a;
      display: flex;
      align-items: center;
      gap: 0.5rem;
      flex-wrap: wrap;
      border-top: 1px solid var(--border-light);
      padding-top: 1rem;
      margin-top: 0.5rem;
    }

    .article h2 {
      font-size: 1.7rem;
      font-weight: 600;
      margin: 2rem 0 1rem;
      letter-spacing: -0.01em;
      color: #1e1e2a;
    }
    .article h3 {
      font-size: 1.25rem;
      font-weight: 600;
      margin: 1.5rem 0 0.5rem;
      color: #1e1e2a;
    }
    .article p {
      margin: 0 0 1.2rem;
      color: #2a2a38;
    }
    .article ul, .article ol {
      margin: 0 0 1.5rem 1.5rem;
      color: #2a2a38;
    }
    .article li { margin-bottom: 0.4rem; }

    .note {
      background: var(--bg-soft);
      padding: 1.2rem 1.5rem;
      border-radius: 12px;
      border-left: 4px solid var(--primary);
      margin: 1.8rem 0;
    }
    .note strong { display: block; margin-bottom: 0.3rem; color: #1e1e2a; }
    .note p { margin: 0; }

    .article-cta, .final-cta {
      background: var(--bg-soft);
      padding: 1.8rem 2rem;
      border-radius: 18px;
      text-align: center;
      margin: 2.5rem 0 1.5rem;
      border: 1px solid var(--border-light);
    }
    .article-cta h3, .final-cta h2 {
      font-size: 1.4rem;
      margin-top: 0;
      margin-bottom: 0.5rem;
    }
    .article-cta p, .final-cta p { margin-bottom: 1.2rem; }

    .cta-button {
      display: inline-block;
      background: #1e1e2a;
      color: #fff;
      padding: 0.7rem 2.2rem;
      border-radius: 40px;
      font-weight: 600;
      text-decoration: none;
      font-size: 1rem;
      transition: background 0.2s;
    }
    .cta-button:hover { background: var(--primary-dark); }

    .faq details {
      border-bottom: 1px solid var(--border-light);
      padding: 1rem 0;
    }
    .faq summary {
      font-weight: 600;
      cursor: pointer;
      font-size: 1.05rem;
      color: #1e1e2a;
    }
    .faq summary:hover { color: var(--primary); }
    .faq details p { margin-top: 0.8rem; padding-right: 0.5rem; }

    /* ----- TOC as two columns (In this guide) ----- */
    .toc {
      background: var(--bg-soft);
      padding: 1.2rem 1.8rem;
      border-radius: 16px;
      margin: 1.8rem 0 2rem;
      border: 1px solid var(--border-light);
    }
    .toc-title {
      font-weight: 700;
      font-size: 1rem;
      margin-bottom: 0.75rem;
      color: #1e1e2a;
    }
    .toc-title i {
      margin-right: 0.4rem;
      color: var(--primary);
    }
    .toc-grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 0.2rem 1.8rem;
      list-style: none;
      margin: 0;
      padding: 0;
    }
    .toc-grid li {
      margin-bottom: 0.2rem;
    }
    .toc-grid li a {
      text-decoration: none;
      color: #2f2f3d;
      font-size: 0.92rem;
      border-bottom: 1px dotted #d0cac2;
      display: inline-block;
      padding: 0.1rem 0;
    }
    .toc-grid li a i {
      margin-right: 0.3rem;
      font-size: 0.75rem;
      color: var(--primary);
      opacity: 0.7;
    }
    .toc-grid li a:hover {
      color: var(--primary);
      border-bottom-color: var(--primary);
    }

    /* ===== SIDEBAR AS MENU ===== */
    .sidebar {
      background: #ffffff;
      border-radius: 20px;
      padding: 1.8rem 1.5rem 2rem;
      border: 1px solid var(--border-light);
      box-shadow: 0 4px 16px rgba(0,0,0,0.02);
      position: static;
      top: 6rem;
      align-self: start;
    }
    .sidebar-title {
      font-size: 1.2rem;
      font-weight: 700;
      letter-spacing: -0.01em;
      padding-bottom: 0.75rem;
      border-bottom: 2px solid var(--border-light);
      margin-bottom: 1.5rem;
      color: #1e1e2a;
      display: flex;
      align-items: center;
      gap: 0.5rem;
    }
    .sidebar-title i {
      color: var(--primary);
      font-size: 1.3rem;
    }

    /* menu items */
    .sidebar-menu {
      list-style: none;
      padding: 0;
      margin: 0;
    }
    .sidebar-menu > li {
      margin-bottom: 0.3rem;
    }
    .sidebar-menu > li > a {
      display: flex;
      align-items: center;
      gap: 0.7rem;
      padding: 0.6rem 0.8rem;
      border-radius: 12px;
      text-decoration: none;
      color: #2c2c3a;
      font-weight: 500;
      font-size: 0.95rem;
      transition: background 0.15s, color 0.15s;
      border-left: 3px solid transparent;
    }
    .sidebar-menu > li > a i {
      width: 1.4rem;
      text-align: center;
      color: var(--primary);
      opacity: 0.7;
      font-size: 1rem;
    }
    .sidebar-menu > li > a:hover {
      background: var(--bg-soft);
      color: var(--primary);
      border-left-color: var(--primary);
    }
    .sidebar-menu > li > a:hover i {
      opacity: 1;
    }
    .sidebar-menu > li > a.active {
      background: #f0ebe4;
      font-weight: 600;
      border-left-color: var(--primary);
      color: #1e1e2a;
    }
    .sidebar-menu > li > a.active i {
      opacity: 1;
    }

    /* sub-menu */
    .sidebar-menu .sub-menu {
      list-style: none;
      padding: 0;
      margin: 0.2rem 0 0.4rem 1.8rem;
    }
    .sidebar-menu .sub-menu li a {
      display: flex;
      align-items: center;
      gap: 0.5rem;
      padding: 0.4rem 0.8rem;
      border-radius: 8px;
      text-decoration: none;
      color: #3d3d4d;
      font-size: 0.9rem;
      transition: background 0.15s, color 0.15s;
    }
    .sidebar-menu .sub-menu li a i {
      width: 1.2rem;
      text-align: center;
      font-size: 0.75rem;
      color: var(--primary);
      opacity: 0.5;
    }
    .sidebar-menu .sub-menu li a:hover {
      background: var(--bg-soft);
      color: var(--primary);
    }
    .sidebar-menu .sub-menu li a:hover i {
      opacity: 0.9;
    }
    .sidebar-menu .sub-menu li a.active-sub {
      color: var(--primary);
      font-weight: 500;
    }
    .sidebar-menu .sub-menu li a.active-sub i {
      opacity: 1;
    }

    .sidebar-divider {
      height: 1px;
      background: var(--border-light);
      margin: 1.2rem 0;
    }

    .sidebar-tag {
      display: inline-block;
      background: var(--bg-soft);
      padding: 0.2rem 0.9rem;
      border-radius: 30px;
      font-size: 0.75rem;
      font-weight: 500;
      color: #4a4a5a;
      letter-spacing: 0.01em;
      margin-top: 0.5rem;
    }
    .sidebar-tag i {
      margin-right: 0.3rem;
      font-size: 0.7rem;
    }

    /* ----- footer ----- */
    .site-footer {
      background: #ffffff;
      border-top: 1px solid var(--border-light);
      padding: 1.5rem 2rem;
      margin-top: 2rem;
    }
    .footer-inner {
      max-width: 1400px;
      margin: 0 auto;
      display: flex;
      flex-wrap: wrap;
      justify-content: space-between;
      align-items: center;
      gap: 1rem;
      font-size: 0.9rem;
      color: #4a4a5a;
    }
    .footer-links {
      display: flex;
      gap: 1.8rem;
    }
    .footer-links a {
      text-decoration: none;
      color: #4a4a5a;
    }
    .footer-links a:hover { color: var(--primary); }
    .footer-links a i {
      margin-right: 0.3rem;
    }

    /* ===== RESPONSIVE ===== */
    @media (max-width: 1024px) {
      .page-wrapper {
        grid-template-columns: 1fr 280px;
        gap: 2rem;
      }
    }

    @media (max-width: 992px) {
      .page-wrapper {
        grid-template-columns: 1fr;
        gap: 2rem;
      }
      .sidebar {
        position: static;
        width: 100%;
        order: 2;
      }
      /* sidebar menu becomes horizontal accordion style on tablet */
      .sidebar-menu {
        display: grid;
        grid-template-columns: 1fr 1fr;
        gap: 0.3rem 1.5rem;
      }
      .sidebar-menu > li {
        margin-bottom: 0;
      }
      .sidebar-menu .sub-menu {
        margin-left: 1.2rem;
        grid-column: 1 / -1;
      }
      .sidebar-divider {
        display: none;
      }
      .sidebar-tag-wrap {
        grid-column: 1 / -1;
        margin-top: 0.5rem;
      }
    }

    @media (max-width: 768px) {
      .hamburger {
        display: block;
      }
      .nav {
        display: none;
        width: 100%;
        flex-direction: column;
        align-items: stretch;
        gap: 0.5rem;
        padding-top: 1rem;
        border-top: 1px solid var(--border-light);
      }
      .nav.open {
        display: flex;
      }
      .nav a {
        padding: 0.4rem 0;
      }
      .nav-button {
        text-align: center;
      }
      .header-inner {
        flex-wrap: wrap;
      }
      .logo {
        flex: 1;
      }
      .article-wrapper {
        padding: 1.2rem;
      }
      h1 {
        font-size: 1.6rem;
      }
      .toc-grid {
        grid-template-columns: 1fr;
      }
      .sidebar-menu {
        grid-template-columns: 1fr;
      }
      .sidebar-menu .sub-menu {
        margin-left: 1.2rem;
      }
      .footer-inner {
        flex-direction: column;
        text-align: center;
      }
      .footer-links {
        flex-wrap: wrap;
        justify-content: center;
      }
    }

    @media (max-width: 480px) {
      .logo {
        font-size: 1.2rem;
      }
      .logo img {
        width: 30px;
        height: 30px;
      }
      .article-cta, .final-cta {
        padding: 1.2rem 1rem;
      }
      .cta-button {
        padding: 0.6rem 1.5rem;
        font-size: 0.9rem;
      }
      .sidebar {
        padding: 1.2rem 1rem;
      }
    }

    /* small fix for sidebar tags on grid */
    .sidebar-tag-wrap {
      margin-top: 1.2rem;
      border-top: 1px solid var(--border-light);
      padding-top: 1.2rem;
      grid-column: 1 / -1;
    }