:root {
      --paper: #eef3f6;
      --sheet: #ffffff;
      --ink: #16222e;
      --ink-soft: #52616f;
      --ink-faint: #93a1ad;
      --grid: rgba(29, 95, 191, 0.07);
      --line: #d5dee6;
      --line-blue: #b9cde8;
      --blue: #1d5fbf;
      --blue-deep: #123d7d;
      --blue-wash: #e8f0fb;
      --orange: #e8641f;
      --orange-wash: #fdeadd;
      --green: #218a5b;
      --green-wash: #e6f3ec;
      --red: #d64545;
      --font-body: "Noto Sans SC", sans-serif;
      --font-mono: "JetBrains Mono", monospace;
    }

    * { margin: 0; padding: 0; box-sizing: border-box; }
    html { scroll-behavior: smooth; }
    body {
      background: var(--paper);
      color: var(--ink);
      font-family: var(--font-body);
      font-size: 16px;
      line-height: 1.8;
      overflow-x: hidden;
    }
    body::before {
      content: "";
      position: fixed;
      inset: 0;
      background-image:
        linear-gradient(var(--grid) 1px, transparent 1px),
        linear-gradient(90deg, var(--grid) 1px, transparent 1px);
      background-size: 28px 28px;
      pointer-events: none;
      z-index: 0;
    }
    ::selection { background: var(--blue); color: #fff; }
    a { color: inherit; text-decoration: none; }
    ul, ol { list-style: none; }
    button { font-family: inherit; }

    .wrap { max-width: 1220px; margin: 0 auto; padding: 0 28px; position: relative; z-index: 1; }
    .mono { font-family: var(--font-mono); }

    .reveal {
      opacity: 0;
      transform: translateY(24px);
      transition: opacity 0.7s ease, transform 0.7s cubic-bezier(0.22, 1, 0.36, 1);
    }
    .reveal.is-in { opacity: 1; transform: none; }

    .ticks { position: relative; }
    .ticks::before, .ticks::after,
    .ticks > .tk::before, .ticks > .tk::after {
      content: "";
      position: absolute;
      width: 14px; height: 14px;
      border-color: var(--blue);
      border-style: solid;
      border-width: 0;
      opacity: 0.75;
      pointer-events: none;
      z-index: 3;
    }
    .ticks::before { top: -1px; left: -1px; border-top-width: 2px; border-left-width: 2px; }
    .ticks::after { top: -1px; right: -1px; border-top-width: 2px; border-right-width: 2px; }
    .ticks > .tk::before { bottom: -1px; left: -1px; border-bottom-width: 2px; border-left-width: 2px; }
    .ticks > .tk::after { bottom: -1px; right: -1px; border-bottom-width: 2px; border-right-width: 2px; }

    /* ============ Top bar (shared) ============ */
    .topbar {
      position: sticky; top: 0; z-index: 50;
      background: rgba(255, 255, 255, 0.92);
      backdrop-filter: blur(10px);
      border-bottom: 1px solid var(--line-blue);
    }
    .topbar__inner { display: flex; align-items: center; gap: 26px; height: 62px; }
    .brand { display: flex; align-items: center; gap: 11px; font-weight: 900; font-size: 20px; letter-spacing: 0.04em; }
    .brand__mark {
      width: 36px; height: 36px;
      border: 1.5px dashed var(--blue);
      border-radius: 8px;
      display: grid; place-items: center;
      background: var(--blue-wash);
      overflow: hidden;
    }
    .brand__mark img { width: 27px; height: 27px; object-fit: contain; display: block; }
    .brand__sheet {
      font-family: var(--font-mono); font-size: 10px; font-weight: 400;
      color: var(--blue); border: 1px solid var(--line-blue); background: var(--blue-wash);
      padding: 2px 8px; border-radius: 3px; letter-spacing: 0.14em;
    }
    .main-nav { display: flex; align-items: center; gap: 2px; margin-left: 8px; }
    .main-nav a {
      font-size: 14px; padding: 6px 16px; color: var(--ink-soft); border-radius: 4px;
      transition: color 0.2s, background 0.2s; font-weight: 500;
    }
    .main-nav a .no { font-family: var(--font-mono); font-size: 10px; color: var(--ink-faint); margin-right: 6px; }
    .main-nav a:hover { color: var(--blue); background: var(--blue-wash); }
    .main-nav a.is-active { color: var(--blue); font-weight: 700; }
    .main-nav a.is-active .no { color: var(--orange); }
    .topbar__right { margin-left: auto; display: flex; align-items: center; gap: 12px; }

    .lang-switch { position: relative; }
    .lang-switch__btn {
      display: flex; align-items: center; gap: 7px; background: transparent;
      border: 1px solid var(--line); color: var(--ink-soft); font-size: 12.5px;
      font-family: var(--font-mono); cursor: pointer; padding: 7px 13px; border-radius: 4px;
      transition: border-color 0.2s, color 0.2s;
    }
    .lang-switch__btn:hover { border-color: var(--blue); color: var(--blue); }
    .lang-switch__menu {
      position: absolute; top: calc(100% + 8px); right: 0; min-width: 142px;
      background: var(--sheet); border: 1px solid var(--line-blue); border-radius: 6px;
      box-shadow: 0 12px 28px rgba(18, 61, 125, 0.14); padding: 6px; display: none; z-index: 60;
    }
    .lang-switch__menu.is-open { display: block; }
    .lang-switch__menu li { border-radius: 4px; overflow: hidden; }
    .lang-switch__menu li > a,
    .lang-switch__menu li.is-current {
      padding: 8px 12px; font-size: 13px; color: var(--ink-soft); cursor: pointer;
      border-radius: 4px; display: flex; justify-content: space-between; align-items: center;
      text-decoration: none;
    }
    .lang-switch__menu li > a:hover { background: var(--blue-wash); color: var(--ink); }
    .lang-switch__menu li.is-current { color: var(--blue); font-weight: 700; }
    .lang-switch__menu li.is-current::after { content: "✓"; font-size: 11px; }

    .nav-burger {
      display: none; background: var(--sheet); border: 1px solid var(--line); color: var(--ink);
      width: 38px; height: 38px; border-radius: 6px; font-size: 15px; cursor: pointer;
    }

    .btn {
      display: inline-flex; align-items: center; gap: 10px; font-size: 15px; font-weight: 700;
      padding: 14px 28px; border-radius: 6px; cursor: pointer; border: 1.5px solid transparent;
      transition: transform 0.18s, box-shadow 0.18s, background 0.18s, color 0.18s;
    }
    .btn--primary { background: var(--blue); color: #fff; box-shadow: 0 10px 24px rgba(29, 95, 191, 0.3); }
    .btn--primary:hover { transform: translateY(-3px); box-shadow: 0 16px 30px rgba(29, 95, 191, 0.38); background: var(--blue-deep); }
    .btn--ghost { background: var(--sheet); color: var(--ink); border-color: var(--line); }
    .btn--ghost:hover { transform: translateY(-3px); border-color: var(--blue); color: var(--blue); }

    /* ============ Page header: sheet ============ */
    .faq-hero { padding: 46px 0 0; }
    .sheet {
      background: var(--sheet);
      border: 1.5px solid var(--blue);
      box-shadow: 0 24px 60px rgba(18, 61, 125, 0.12);
      position: relative;
      background-image:
        linear-gradient(var(--grid) 1px, transparent 1px),
        linear-gradient(90deg, var(--grid) 1px, transparent 1px);
      background-size: 28px 28px;
    }
    .sheet::before { content: ""; position: absolute; inset: 10px; border: 1px solid var(--line-blue); pointer-events: none; }
    .sheet__body { padding: 52px 54px 40px; position: relative; }
    .sheet__label {
      font-family: var(--font-mono); font-size: 11px; letter-spacing: 0.28em; color: var(--blue);
      display: flex; align-items: flex-start; gap: 8px; margin-bottom: 20px;
      padding-right: 170px;
    }
    .sheet__label i { margin-top: 2px; }
    .sheet__rev {
      position: absolute; top: 22px; right: 54px; font-family: var(--font-mono);
      font-size: 11px; color: var(--ink-faint); letter-spacing: 0.14em;
    }
    .sheet__rev b { color: var(--orange); font-weight: 600; }

    .faq-hero h1 {
      font-weight: 900;
      font-size: clamp(30px, 4.2vw, 48px);
      line-height: 1.35;
      max-width: 760px;
    }
    .faq-hero h1 span { color: var(--blue); }
    .faq-hero__sub {
      margin-top: 18px; color: var(--ink-soft); font-size: 15.5px; max-width: 660px;
    }
    .faq-hero__sub strong { color: var(--ink); }

    .jump-row { margin-top: 30px; display: flex; flex-wrap: wrap; gap: 10px; }
    .jump-row a {
      display: flex; align-items: center; gap: 9px;
      border: 1px solid var(--line);
      border-radius: 999px;
      padding: 9px 18px 9px 14px;
      font-size: 13.5px;
      font-weight: 600;
      color: var(--ink-soft);
      background: var(--paper);
      transition: all 0.2s;
    }
    .jump-row a i { color: var(--blue); font-size: 14px; }
    .jump-row a:hover { border-color: var(--blue); color: var(--blue); background: var(--blue-wash); transform: translateY(-2px); }
    .jump-row a .jc { font-family: var(--font-mono); font-size: 10.5px; color: var(--ink-faint); }

    .titleblock {
      display: grid;
      grid-template-columns: 1.6fr 1fr 1fr 1fr 1fr;
      border-top: 1.5px solid var(--blue);
      background: var(--sheet);
      position: relative;
      z-index: 1;
    }
    .titleblock > div { padding: 10px 18px 12px; border-right: 1px solid var(--line-blue); }
    .titleblock > div:last-child { border-right: none; }
    .titleblock dt { font-family: var(--font-mono); font-size: 9.5px; letter-spacing: 0.2em; color: var(--ink-faint); }
    .titleblock dd { font-size: 13.5px; font-weight: 700; color: var(--ink); font-family: var(--font-mono); }
    .titleblock dd a { color: var(--blue); border-bottom: 1px dashed var(--line-blue); }

    /* ============ Section heads ============ */
    .faq-sec { padding: 70px 0 10px; scroll-margin-top: 80px; }
    .sec-head { margin-bottom: 32px; display: flex; align-items: flex-start; gap: 20px; }
    .sec-head__no {
      font-family: var(--font-mono); font-size: 30px; font-weight: 700; color: var(--line-blue);
      line-height: 1; flex-shrink: 0; padding-top: 4px;
    }
    .sec-head__tag {
      font-family: var(--font-mono); font-size: 11px; letter-spacing: 0.28em; color: var(--blue);
      display: flex; align-items: center; gap: 12px; margin-bottom: 10px;
    }
    .sec-head__tag::after { content: ""; width: 90px; height: 1px; background: var(--blue); }
    .sec-head h2 { font-weight: 900; font-size: clamp(22px, 2.8vw, 30px); line-height: 1.4; }
    .sec-head p { color: var(--ink-soft); font-size: 14px; max-width: 620px; margin-top: 6px; }

    /* ============ FAQ accordion ============ */
    .faq__list { display: flex; flex-direction: column; gap: 12px; margin-bottom: 20px; }
    .faq__item {
      background: var(--sheet);
      border: 1px solid var(--line-blue);
      border-radius: 6px;
    }
    .faq__item summary {
      list-style: none;
      cursor: pointer;
      padding: 18px 24px;
      font-weight: 700;
      font-size: 15px;
      display: flex;
      align-items: center;
      gap: 14px;
    }
    .faq__item summary::-webkit-details-marker { display: none; }
    .faq__item summary .q-no {
      font-family: var(--font-mono); font-size: 11px; color: var(--blue);
      background: var(--blue-wash); border: 1px solid var(--line-blue); border-radius: 4px;
      padding: 2px 7px; flex-shrink: 0;
    }
    .faq__item summary::after {
      content: "\f078";
      font-family: "Font Awesome 6 Free";
      font-weight: 900;
      margin-left: auto;
      font-size: 12px;
      color: var(--ink-faint);
      transition: transform 0.2s;
    }
    .faq__item[open] summary::after { transform: rotate(180deg); }
    .faq__item .faq__a {
      padding: 0 24px 20px 68px;
      font-size: 14px;
      color: var(--ink-soft);
    }
    .faq__item .faq__a code {
      font-family: var(--font-mono); font-size: 12px; background: var(--paper);
      border: 1px solid var(--line); border-radius: 4px; padding: 2px 7px; color: var(--blue-deep);
    }

    /* ============ Still stuck strip ============ */
    .still-stuck { padding: 20px 0 96px; }
    .still-stuck__box {
      border: 1.5px dashed var(--blue);
      background: var(--sheet);
      padding: 36px 40px;
      display: flex;
      align-items: center;
      justify-content: space-between;
      gap: 24px;
      flex-wrap: wrap;
    }
    .still-stuck__box h2 { font-weight: 900; font-size: 20px; margin-bottom: 6px; }
    .still-stuck__box p { color: var(--ink-soft); font-size: 13.5px; max-width: 480px; }
    .still-stuck__actions { display: flex; gap: 12px; flex-wrap: wrap; }

    /* ============ Footer (shared) ============ */
    .site-foot { border-top: 1.5px solid var(--blue); background: var(--sheet); padding: 62px 0 0; position: relative; z-index: 1; }
    .foot-grid { display: grid; grid-template-columns: 1.4fr 1fr 1fr 1.1fr; gap: 44px; padding-bottom: 50px; }
    .foot-brand p { color: var(--ink-soft); font-size: 13.5px; margin-top: 16px; max-width: 300px; }
    .foot-col h4 {
      font-family: var(--font-mono); font-size: 10.5px; letter-spacing: 0.26em; color: var(--blue);
      margin-bottom: 18px; font-weight: 400; display: flex; align-items: center; gap: 10px;
    }
    .foot-col h4::after { content: ""; flex: 1; height: 1px; background: var(--line); }
    .foot-col ul li { margin-bottom: 11px; }
    .foot-col ul a { font-size: 14px; color: var(--ink-soft); transition: color 0.2s, padding-left 0.2s; }
    .foot-col ul a:hover { color: var(--blue); padding-left: 6px; }
    .foot-col ul a i { font-size: 11px; margin-right: 8px; color: var(--ink-faint); }
    .foot-langs { display: flex; flex-wrap: wrap; gap: 8px; }
    .foot-langs span {
      font-family: var(--font-mono); font-size: 11.5px; border: 1px solid var(--line); border-radius: 4px;
      padding: 5px 13px; color: var(--ink-soft); cursor: pointer; transition: all 0.2s; background: var(--paper);
    }
    .foot-langs span:hover, .foot-langs span.on { color: #fff; background: var(--blue); border-color: var(--blue); }
    .foot-word {
      font-weight: 900; font-size: clamp(70px, 12.5vw, 172px); line-height: 1; text-align: center;
      color: transparent; -webkit-text-stroke: 1px var(--line-blue); user-select: none;
      letter-spacing: 0.08em; transform: translateY(8px);
    }
    .foot-base {
      border-top: 1px solid var(--line); padding: 20px 0; display: flex; justify-content: space-between;
      align-items: center; gap: 16px; flex-wrap: wrap; font-family: var(--font-mono); font-size: 11.5px; color: var(--ink-faint);
    }
    .foot-base a { color: var(--ink-soft); }
    .foot-base a:hover { color: var(--blue); }

    @media (max-width: 1024px) {
      .titleblock { grid-template-columns: 1.6fr 1fr 1fr; }
      .titleblock > div:nth-child(n+4) { border-top: 1px solid var(--line-blue); }
      .foot-grid { grid-template-columns: 1fr 1fr; }
    }

    @media (max-width: 720px) {
      .wrap { padding: 0 18px; }
      .brand__sheet { display: none; }
      .main-nav {
        display: none; position: absolute; top: 62px; left: 0; right: 0;
        flex-direction: column; align-items: stretch; background: var(--sheet);
        border-bottom: 1.5px solid var(--blue); padding: 10px 20px 18px; margin-left: 0;
      }
      .main-nav.is-open { display: flex; }
      .main-nav a { padding: 12px 8px; font-size: 16px; }
      .nav-burger { display: block; }

      .sheet__body { padding: 44px 22px 28px; }
      .sheet__label { padding-right: 118px; font-size: 9.5px; letter-spacing: 0.16em; }
      .sheet__rev { right: 22px; top: 18px; }
      .titleblock { grid-template-columns: 1fr 1fr; }
      .titleblock > div:nth-child(n+3) { border-top: 1px solid var(--line-blue); }

      .sec-head { flex-direction: column; gap: 8px; }
      .faq__item .faq__a { padding: 0 20px 18px 20px; }
      .still-stuck__box { padding: 28px 22px; }
      .foot-grid { grid-template-columns: 1fr; gap: 32px; }
      .foot-base { justify-content: center; text-align: center; }
    }

    @media (prefers-reduced-motion: reduce) {
      *, *::before, *::after { animation-duration: 0.01ms !important; transition-duration: 0.01ms !important; }
      html { scroll-behavior: auto; }
    }