:root {
    --white: #ffffff;
    --gray-50: #fafafa;
    --gray-100: #f5f5f7;
    --gray-200: #e8e8ed;
    --gray-300: #d2d2d7;
    --gray-400: #adadb8;
    --gray-500: #86868b;
    --gray-700: #424245;
    --gray-900: #1d1d1f;
    --blue: #0071e3;
    --blue-light: #e8f0fb;
    --blue-hover: #0077ed;
    --green: #30d158;
    --orange: #ff9f0a;
    --red: #ff453a;
    --sidebar-width: 260px;
  }

  * { margin: 0; padding: 0; box-sizing: border-box; }
  html { scroll-behavior: smooth; }

  body {
    font-family: -apple-system, BlinkMacSystemFont, 'SF Pro Text', 'Helvetica Neue', sans-serif;
    background: var(--white);
    color: var(--gray-900);
    -webkit-font-smoothing: antialiased;
  }

  /* ── TOP NAV ── */
  .topnav {
    position: fixed; top: 0; left: 0; right: 0; z-index: 200;
    height: 52px;
    background: rgba(255,255,255,0.92);
    backdrop-filter: saturate(180%) blur(20px);
    -webkit-backdrop-filter: saturate(180%) blur(20px);
    border-bottom: 1px solid var(--gray-200);
    display: flex; align-items: center; justify-content: space-between;
    padding: 0 24px;
  }
  .topnav-left { display: flex; align-items: center; gap: 8px; }
  .topnav-brand { font-size: 15px; font-weight: 600; color: var(--gray-900); text-decoration: none; letter-spacing: -0.2px; }
  .topnav-sep { color: var(--gray-300); font-size: 18px; font-weight: 200; }
  .topnav-section { font-size: 15px; color: var(--gray-500); font-weight: 400; }
  .topnav-right { display: flex; align-items: center; gap: 16px; }
  .topnav-right a { font-size: 13px; color: var(--gray-500); text-decoration: none; transition: color 0.2s; }
  .topnav-right a:hover { color: var(--gray-900); }
  .topnav-right a.active { color: var(--blue); font-weight: 500; }
  .back-link { display: flex; align-items: center; gap: 5px; font-size: 13px; color: var(--blue); text-decoration: none; }
  .back-link:hover { text-decoration: underline; }

  /* ── LAYOUT ── */
  .layout {
    display: flex;
    padding-top: 52px;
    min-height: 100vh;
  }

  /* ── SIDEBAR ── */
  .sidebar {
    width: var(--sidebar-width);
    flex-shrink: 0;
    position: fixed;
    top: 52px; left: 0; bottom: 0;
    overflow-y: auto;
    border-right: 1px solid var(--gray-200);
    padding: 24px 0 48px;
    background: var(--gray-50);
  }
  .sidebar::-webkit-scrollbar { width: 4px; }
  .sidebar::-webkit-scrollbar-thumb { background: var(--gray-300); border-radius: 2px; }

  .sidebar-section { margin-bottom: 28px; }
  .sidebar-section-title {
    font-size: 11px; font-weight: 600; text-transform: uppercase;
    letter-spacing: 0.08em; color: var(--gray-400);
    padding: 0 20px; margin-bottom: 6px;
  }
  .sidebar-link {
    display: flex; align-items: center; gap: 8px;
    padding: 6px 20px; font-size: 14px; color: var(--gray-700);
    text-decoration: none; border-radius: 0;
    transition: background 0.15s, color 0.15s;
    cursor: pointer; border: none; background: none; width: 100%; text-align: left;
  }
  .sidebar-link:hover { background: var(--gray-200); color: var(--gray-900); }
  .sidebar-link.active { background: var(--blue-light); color: var(--blue); font-weight: 500; }
  .sidebar-link .dot { width: 6px; height: 6px; border-radius: 50%; flex-shrink: 0; }
  .dot-green { background: var(--green); }
  .dot-orange { background: var(--orange); }
  .dot-gray { background: var(--gray-300); }

  /* ── MAIN CONTENT ── */
  .main {
    margin-left: var(--sidebar-width);
    flex: 1;
    min-width: 0;
  }

  /* ── PAGE ── */
  .page { display: none; }
  .page.active { display: block; }

  /* ── CONTENT AREA ── */
  .content {
    max-width: 740px;
    margin: 0 auto;
    padding: 48px 48px 96px;
  }

  /* ── TYPOGRAPHY ── */
  .page-eyebrow { font-size: 13px; font-weight: 500; color: var(--blue); text-transform: uppercase; letter-spacing: 0.06em; margin-bottom: 10px; }
  .page-title { font-size: clamp(28px, 4vw, 40px); font-weight: 700; letter-spacing: -0.025em; line-height: 1.1; margin-bottom: 10px; }
  .page-sub { font-size: 17px; color: var(--gray-500); line-height: 1.6; margin-bottom: 40px; padding-bottom: 40px; border-bottom: 1px solid var(--gray-200); }

  h2.doc-h2 { font-size: 22px; font-weight: 600; letter-spacing: -0.02em; margin: 48px 0 14px; }
  h3.doc-h3 { font-size: 17px; font-weight: 600; margin: 28px 0 10px; }
  p.doc-p { font-size: 16px; color: var(--gray-700); line-height: 1.7; margin-bottom: 16px; }
  ul.doc-ul { padding-left: 20px; margin-bottom: 16px; display: flex; flex-direction: column; gap: 7px; }
  ul.doc-ul li { font-size: 15px; color: var(--gray-700); line-height: 1.6; }
  ol.doc-ol { padding-left: 20px; margin-bottom: 16px; display: flex; flex-direction: column; gap: 8px; }
  ol.doc-ol li { font-size: 15px; color: var(--gray-700); line-height: 1.6; }

  /* callout boxes */
  .callout {
    border-radius: 12px; padding: 16px 20px;
    margin: 24px 0; display: flex; gap: 12px; align-items: flex-start;
  }
  .callout.info { background: var(--blue-light); border-left: 3px solid var(--blue); }
  .callout.warning { background: rgba(255,159,10,0.1); border-left: 3px solid var(--orange); }
  .callout.success { background: rgba(48,209,88,0.1); border-left: 3px solid var(--green); }
  .callout-icon { font-size: 17px; flex-shrink: 0; margin-top: 1px; }
  .callout-text { font-size: 14px; color: var(--gray-700); line-height: 1.6; }
  .callout-text strong { color: var(--gray-900); }

  /* code inline */
  code {
    background: var(--gray-100); border: 1px solid var(--gray-200);
    border-radius: 5px; padding: 2px 7px;
    font-family: 'SF Mono', 'Menlo', monospace; font-size: 13px;
    color: var(--gray-900);
  }

  /* step list */
  .steps { display: flex; flex-direction: column; gap: 16px; margin: 24px 0; }
  .step { display: flex; gap: 16px; align-items: flex-start; }
  .step-num {
    width: 28px; height: 28px; border-radius: 50%;
    background: var(--blue); color: white;
    font-size: 13px; font-weight: 600;
    display: flex; align-items: center; justify-content: center;
    flex-shrink: 0; margin-top: 1px;
  }
  .step-text { font-size: 15px; color: var(--gray-700); line-height: 1.6; padding-top: 3px; }
  .step-text strong { color: var(--gray-900); }

  /* divider */
  .doc-divider { border: none; border-top: 1px solid var(--gray-200); margin: 40px 0; }

  /* ── CHANGELOG ── */
  .changelog-entry { margin-bottom: 56px; }
  .changelog-header { display: flex; align-items: center; gap: 12px; margin-bottom: 20px; padding-bottom: 16px; border-bottom: 1px solid var(--gray-200); }
  .version-badge {
    font-size: 15px; font-weight: 600; color: white;
    background: var(--gray-900); border-radius: 8px;
    padding: 4px 12px; letter-spacing: -0.02em;
  }
  .version-badge.latest { background: var(--blue); }
  .changelog-date { font-size: 14px; color: var(--gray-500); }
  .changelog-tag {
    font-size: 11px; font-weight: 600; text-transform: uppercase; letter-spacing: 0.06em;
    padding: 3px 8px; border-radius: 6px; margin-left: auto;
  }
  .tag-major { background: rgba(0,113,227,0.1); color: var(--blue); }
  .tag-minor { background: rgba(48,209,88,0.1); color: #1a7f37; }
  .tag-patch { background: var(--gray-100); color: var(--gray-500); }

  .changelog-items { display: flex; flex-direction: column; gap: 10px; }
  .changelog-item { display: flex; gap: 10px; align-items: flex-start; }
  .changelog-item-type {
    font-size: 11px; font-weight: 600; text-transform: uppercase; letter-spacing: 0.05em;
    padding: 2px 7px; border-radius: 5px; flex-shrink: 0; margin-top: 2px;
  }
  .type-new { background: rgba(48,209,88,0.12); color: #1a7f37; }
  .type-fix { background: rgba(255,159,10,0.12); color: #b25000; }
  .type-improved { background: rgba(0,113,227,0.1); color: var(--blue); }
  .type-removed { background: rgba(255,69,58,0.1); color: var(--red); }
  .changelog-item-text { font-size: 15px; color: var(--gray-700); line-height: 1.5; }

  /* ── VERSION HISTORY TABLE ── */
  .version-table { width: 100%; border-collapse: collapse; margin: 24px 0; }
  .version-table th { font-size: 12px; font-weight: 600; text-transform: uppercase; letter-spacing: 0.06em; color: var(--gray-500); text-align: left; padding: 10px 14px; border-bottom: 1px solid var(--gray-200); }
  .version-table td { font-size: 14px; color: var(--gray-700); padding: 12px 14px; border-bottom: 1px solid var(--gray-200); vertical-align: top; }
  .version-table tr:last-child td { border-bottom: none; }
  .version-table tr:hover td { background: var(--gray-50); }
  .vtag { display: inline-flex; align-items: center; gap: 5px; font-size: 13px; font-weight: 600; color: var(--gray-900); }
  .vcurrent { font-size: 11px; font-weight: 600; background: var(--blue); color: white; padding: 2px 7px; border-radius: 5px; }

  /* ── FAQ ── */
  .faq-item { border-bottom: 1px solid var(--gray-200); }
  .faq-question {
    width: 100%; text-align: left; background: none; border: none;
    padding: 18px 0; cursor: pointer;
    display: flex; align-items: center; justify-content: space-between; gap: 16px;
    font-size: 16px; font-weight: 500; color: var(--gray-900);
    transition: color 0.2s;
  }
  .faq-question:hover { color: var(--blue); }
  .faq-chevron { font-size: 12px; color: var(--gray-400); transition: transform 0.25s; flex-shrink: 0; }
  .faq-item.open .faq-chevron { transform: rotate(180deg); }
  .faq-answer { font-size: 15px; color: var(--gray-700); line-height: 1.7; max-height: 0; overflow: hidden; transition: max-height 0.35s ease, padding 0.25s ease; }
  .faq-item.open .faq-answer { max-height: 400px; padding-bottom: 20px; }

  /* ── RESPONSIVE ── */
  @media (max-width: 768px) {
    .sidebar { display: none; }
    .main { margin-left: 0; }
    .content { padding: 32px 24px 64px; }
    .topnav-right { display: none; }
  }
  .form-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; margin-bottom: 16px; }
  .form-group { display: flex; flex-direction: column; gap: 6px; margin-bottom: 16px; }
  .form-group.full { grid-column: span 2; }
  .form-label { font-size: 13px; font-weight: 500; color: var(--gray-700); }
  .form-input, .form-select, .form-textarea {
    width: 100%;
    background: var(--gray-100);
    border: 1px solid var(--gray-200);
    border-radius: 10px;
    padding: 11px 14px;
    font-size: 15px;
    font-family: inherit;
    color: var(--gray-900);
    transition: border-color 0.2s, box-shadow 0.2s;
    outline: none;
    appearance: none;
  }
  .form-input:focus, .form-select:focus, .form-textarea:focus {
    border-color: var(--blue);
    box-shadow: 0 0 0 3px rgba(0,113,227,0.15);
    background: var(--white);
  }
  .form-input::placeholder, .form-textarea::placeholder { color: var(--gray-400); }
  .form-textarea { resize: vertical; min-height: 130px; line-height: 1.6; }
  .form-select { background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='8' viewBox='0 0 12 8'%3E%3Cpath d='M1 1l5 5 5-5' stroke='%2386868b' stroke-width='1.5' fill='none' stroke-linecap='round'/%3E%3C/svg%3E"); background-repeat: no-repeat; background-position: right 14px center; padding-right: 36px; cursor: pointer; }
  .form-btn {
    background: var(--blue); color: white;
    font-size: 16px; font-weight: 500;
    padding: 12px 28px; border-radius: 980px;
    border: none; cursor: pointer;
    font-family: inherit;
    transition: background 0.2s, transform 0.15s;
    display: inline-flex; align-items: center; gap: 8px;
  }
  .form-btn:hover { background: var(--blue-hover); transform: scale(1.02); }
  .form-btn:active { transform: scale(0.99); }
  .form-footer-note { font-size: 13px; color: var(--gray-500); margin-top: 12px; }

  .contact-cards { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; margin-bottom: 48px; }
  .contact-card {
    background: var(--gray-100); border-radius: 14px; padding: 24px;
    display: flex; flex-direction: column; gap: 8px;
  }
  .contact-card-icon { font-size: 24px; }
  .contact-card-title { font-size: 15px; font-weight: 600; }
  .contact-card-desc { font-size: 13px; color: var(--gray-500); line-height: 1.5; }
  .contact-card a { color: var(--blue); text-decoration: none; font-size: 13px; font-weight: 500; }
  .contact-card a:hover { text-decoration: underline; }

  .success-banner {
    display: none;
    background: rgba(48,209,88,0.1); border: 1px solid rgba(48,209,88,0.3);
    border-radius: 12px; padding: 16px 20px;
    margin-bottom: 28px;
    align-items: center; gap: 12px;
  }
  .success-banner.visible { display: flex; }
  .success-banner-text { font-size: 15px; color: #1a7f37; font-weight: 500; }
  .success-banner-sub { font-size: 13px; color: #2d9e4f; }

  @media (max-width: 600px) {
    .form-grid { grid-template-columns: 1fr; }
    .form-group.full { grid-column: span 1; }
    .contact-cards { grid-template-columns: 1fr; }
  }