.utility-nav {
  position: sticky;
  top: 0;
  z-index: 20;
  display: flex;
  flex-wrap: wrap;
  gap: 0.65rem;
  align-items: center;
  justify-content: space-between;
  padding: 0.9rem 1rem;
  background: rgba(255, 255, 255, 0.82);
  border-bottom: 1px solid var(--line);
  backdrop-filter: blur(10px);
}

.utility-nav__brand {
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  font-size: 0.82rem;
}

.utility-nav__brand-link {
  display: block;
  color: inherit;
  text-decoration: none;
}

.utility-nav__brand-link:hover,
.utility-nav__brand-link:focus-visible {
  color: inherit;
  text-decoration: none;
}

.utility-nav__menu-toggle {
  display: none;
}

.utility-nav__links {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  font-size: 0.95rem;
}

.utility-nav__cluster {
  display: flex;
  flex: 1 1 34rem;
  flex-wrap: wrap;
  gap: 0.75rem;
  align-items: center;
  justify-content: flex-end;
}

.utility-nav .site-language {
  position: relative;
  display: grid;
  gap: 0.3rem;
  min-inline-size: min(20rem, 100%);
}

.utility-nav .site-language__toggle {
  display: none;
}

.utility-nav .site-language__label {
  margin: 0;
  color: var(--muted);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

.utility-nav .site-language__list {
  display: flex;
  flex-wrap: wrap;
  gap: 0.3rem;
}

.utility-nav .site-language__link {
  display: inline-flex;
  flex: 0 1 auto;
  align-items: center;
  justify-content: center;
  min-inline-size: 6.25rem;
  min-block-size: 2.45rem;
  padding-inline: 0.7rem;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: rgba(255, 255, 255, 0.68);
  color: var(--muted);
  font-size: 0.88rem;
  font-weight: 700;
  text-align: center;
  text-decoration: none;
}

.utility-nav .site-language__link[aria-current="page"] {
  border-color: transparent;
  background: linear-gradient(135deg, #22303f, #566c7c);
  color: #f7f3ed;
  text-decoration: none;
}

.utility-nav .site-language--interactive {
  justify-items: end;
  min-inline-size: auto;
}

.utility-nav .site-language--interactive .site-language__label {
  display: none;
}

.utility-nav .site-language--interactive .site-language__toggle {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  align-self: end;
  gap: 0.32rem;
  min-block-size: 1.95rem;
  padding: 0.15rem 0;
  border: none;
  border-radius: 0;
  background: none;
  color: var(--muted);
  font-size: 0.94rem;
  font-weight: 600;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  box-shadow: none;
  white-space: nowrap;
}

.utility-nav .site-language--interactive .site-language__toggle::after {
  content: "";
  inline-size: 0.46rem;
  block-size: 0.46rem;
  border-right: 2px solid currentColor;
  border-bottom: 2px solid currentColor;
  transform: translateY(-0.08rem) rotate(45deg);
  transition: transform 180ms ease;
}

.utility-nav .site-language--interactive.is-open .site-language__toggle::after {
  transform: translateY(0.1rem) rotate(-135deg);
}

.utility-nav .site-language--interactive .site-language__list {
  display: none;
  position: absolute;
  inset-inline-end: 0;
  top: calc(100% + 0.4rem);
  z-index: 40;
  min-inline-size: 11rem;
  max-inline-size: min(16rem, calc(100vw - 1.5rem));
  padding: 0.4rem;
  border: 1px solid rgba(72, 84, 95, 0.14);
  border-radius: 1rem;
  background: rgba(249, 247, 243, 0.97);
  box-shadow: 0 18px 34px rgba(19, 26, 33, 0.18);
  backdrop-filter: blur(16px);
  flex-direction: column;
  gap: 0.3rem;
}

.utility-nav .site-language--interactive.is-open .site-language__list {
  display: flex;
}

.utility-nav .site-language--interactive .site-language__link {
  width: 100%;
  min-inline-size: 0;
  justify-content: flex-start;
  white-space: normal;
  text-decoration: none;
}

.utility-nav--compact {
  position: sticky;
  top: 0;
  min-block-size: 4.1rem;
  padding: 0.85rem 1rem;
  gap: 0.75rem;
}

.utility-nav--compact .utility-nav__brand {
  display: block;
  position: absolute;
  inset-inline-start: 50%;
  transform: translateX(-50%);
  z-index: 0;
  max-inline-size: calc(100% - 8.8rem);
  overflow: hidden;
  color: var(--ink);
  font-size: 0.9rem;
  font-weight: 700;
  letter-spacing: 0.14em;
  text-align: center;
  text-overflow: ellipsis;
  text-transform: uppercase;
  white-space: nowrap;
}

.utility-nav--compact .utility-nav__cluster {
  inline-size: 100%;
  flex: 1 1 auto;
  align-items: center;
  justify-content: space-between;
  gap: 0.6rem;
}

.utility-nav--compact .utility-nav__menu-toggle {
  display: inline-flex;
  order: 1;
  align-items: center;
  justify-content: center;
  gap: 0;
  inline-size: 2.65rem;
  block-size: 2.65rem;
  padding: 0;
  border: 1px solid rgba(72, 84, 95, 0.14);
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.72);
  color: var(--muted);
  font-size: 1.34rem;
  font-weight: 700;
  line-height: 1;
  box-shadow: 0 10px 24px rgba(19, 26, 33, 0.08);
  transition:
    transform 180ms ease,
    background 180ms ease,
    border-color 180ms ease,
    color 180ms ease,
    box-shadow 180ms ease;
}

.utility-nav--compact .utility-nav__menu-toggle::after {
  content: none;
}

.utility-nav--compact .utility-nav__menu-toggle:hover,
.utility-nav--compact .utility-nav__menu-toggle:focus-visible {
  transform: translateY(-1px);
  border-color: rgba(72, 84, 95, 0.22);
  background: rgba(255, 255, 255, 0.92);
  color: var(--ink);
  box-shadow: 0 14px 28px rgba(19, 26, 33, 0.12);
}

.utility-nav--compact .utility-nav__menu-toggle[aria-expanded="true"] {
  background: rgba(255, 255, 255, 0.96);
  color: var(--ink);
}

.utility-nav--compact .site-language {
  order: 2;
  inline-size: auto;
  min-inline-size: auto;
  margin-inline-start: auto;
}

.utility-nav--compact .utility-nav__links--interactive {
  display: none;
  position: absolute;
  inset-inline-start: 1rem;
  top: calc(100% + 0.45rem);
  z-index: 40;
  min-inline-size: min(16rem, calc(100vw - 2rem));
  max-inline-size: min(20rem, calc(100vw - 2rem));
  padding: 0.45rem;
  border: 1px solid rgba(72, 84, 95, 0.14);
  border-radius: 1rem;
  background: rgba(249, 247, 243, 0.97);
  box-shadow: 0 18px 34px rgba(19, 26, 33, 0.18);
  backdrop-filter: blur(16px);
  flex-direction: column;
  gap: 0.2rem;
}

.utility-nav--compact .utility-nav__links--interactive.is-open {
  display: flex;
}

.utility-nav--compact .utility-nav__links--interactive a {
  padding: 0.72rem 0.8rem;
  border-radius: 0.8rem;
  background: rgba(255, 255, 255, 0.68);
  text-decoration: none;
}

.utility-nav--compact .utility-nav__links--interactive .nav-link--mobile-secondary {
  display: inline-flex;
}

.utility-nav--compact .utility-nav__links--interactive a:hover,
.utility-nav--compact .utility-nav__links--interactive a:focus-visible {
  text-decoration: none;
}

.shell {
  display: grid;
  grid-template-columns: minmax(240px, 320px) minmax(0, 1fr);
  gap: 0;
  max-width: 1600px;
  margin: 0 auto;
}

.sidebar {
  position: sticky;
  top: 0;
  align-self: start;
  height: 100vh;
  overflow: auto;
  padding: 2rem 1.5rem 2rem 1.75rem;
  border-right: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.55);
  backdrop-filter: blur(10px);
}

.sidebar h1 {
  margin: 0 0 0.25rem 0;
  font-size: 1.35rem;
  line-height: 1.08;
}

.sidebar .sub {
  color: var(--muted);
  font-size: 0.95rem;
  margin-bottom: 0.2rem;
}

.sidebar .by {
  color: var(--muted);
  margin: 0 0 1.2rem 0;
}

.toc-title {
  font-size: 0.72rem;
  text-transform: uppercase;
  letter-spacing: 0.14em;
  color: var(--muted);
  margin: 1.4rem 0 0.75rem;
}

.sidebar-note {
  margin: 0 0 1rem;
  color: var(--muted);
  font-size: 0.92rem;
  line-height: 1.55;
}

.sidebar-note strong {
  color: var(--ink);
  font-weight: 600;
}

.toc,
.toc ul {
  list-style: none;
  padding: 0;
  margin: 0;
}

.toc > li {
  margin-bottom: 0.75rem;
}

.toc > li > a {
  display: block;
  font-weight: 600;
  color: var(--ink);
  text-decoration: none;
}

.toc ul {
  margin-top: 0.35rem;
  padding-left: 0.8rem;
  border-left: 1px solid var(--line);
}

.toc ul li {
  position: relative;
  margin: 0.32rem 0;
}

.toc ul a {
  display: block;
  margin-inline-start: -0.45rem;
  padding: 0.28rem 0.45rem;
  border-radius: 0.75rem;
  text-decoration: none;
  color: var(--muted);
  transition:
    color 180ms ease,
    background 180ms ease,
    box-shadow 180ms ease;
}

.toc > li > a.is-current-parent {
  color: var(--ink);
  font-weight: 700;
}

.toc > li.is-current-parent > a {
  color: var(--ink);
  font-weight: 700;
}

.toc ul li.is-current {
  z-index: 1;
}

.toc ul li.is-current::before {
  content: "";
  position: absolute;
  inset-inline-start: -1rem;
  top: 0.68rem;
  inline-size: 0.44rem;
  block-size: 0.44rem;
  border-radius: 999px;
  background: linear-gradient(135deg, #8d4f31, #6a3041);
  box-shadow:
    0 0 0 0.24rem rgba(141, 79, 49, 0.14),
    0 0.18rem 0.9rem rgba(106, 48, 65, 0.18);
}

.toc ul a.is-current {
  color: var(--ink);
  font-weight: 700;
  background: linear-gradient(135deg, rgba(255, 251, 247, 0.98), rgba(250, 239, 233, 0.95));
  box-shadow:
    inset 0 0 0 1px rgba(122, 94, 73, 0.16),
    0 0.45rem 1rem rgba(122, 94, 73, 0.1);
}

.mobile-endmatter {
  display: none;
}

.end-link-note {
  margin-top: 1.25rem;
}

.end-link-note p {
  margin: 0;
}

.mobile-download-links {
  display: grid;
  gap: 0.55rem;
}

.mobile-download-links a {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-block-size: 2.7rem;
  padding: 0.75rem 1rem;
  border: 1px solid rgba(72, 84, 95, 0.16);
  border-radius: 0.95rem;
  background: rgba(248, 247, 243, 0.96);
  color: var(--ink);
  font-weight: 600;
  text-decoration: none;
}

.main {
  min-width: 0;
  padding: 3rem clamp(1.2rem, 3vw, 3rem) 5rem;
}

.cover-meta h1,
.title-page h1 {
  font-size: clamp(2rem, 4vw, 3.2rem);
}

.subtitle {
  font-size: clamp(1.05rem, 2vw, 1.35rem);
}

.chapter-title {
  font-size: clamp(1.8rem, 3vw, 2.7rem);
}

.subchapter h3 {
  font-size: clamp(1.25rem, 2vw, 1.6rem);
}

@media (max-width: 980px) {
  .cover-card {
    grid-template-columns: 1fr;
  }

  .utility-nav {
    position: static;
  }

  .utility-nav__cluster {
    inline-size: 100%;
    justify-content: space-between;
  }

  .shell {
    grid-template-columns: 1fr;
  }

  .sidebar {
    position: static;
    height: auto;
    border-right: none;
    border-bottom: 1px solid var(--line);
  }
}

@media (max-width: 640px) {
  .utility-nav__brand {
    display: none;
  }

  .utility-nav__cluster {
    position: relative;
    inline-size: 100%;
    flex: 1 1 auto;
    align-items: center;
    justify-content: space-between;
    gap: 0.5rem;
  }

  .utility-nav .site-language {
    order: 2;
    inline-size: auto;
    min-inline-size: auto;
    margin-inline-start: auto;
  }

  .utility-nav .site-language--interactive {
    justify-items: end;
    min-inline-size: auto;
  }

  .utility-nav .site-language--interactive .site-language__label {
    display: none;
  }

  .utility-nav .site-language--interactive .site-language__toggle {
    min-block-size: 1.85rem;
    font-size: 0.9rem;
  }

  .utility-nav__menu-toggle {
    display: inline-flex;
    order: 1;
    align-items: center;
    justify-content: center;
    gap: 0.32rem;
    min-block-size: 1.85rem;
    padding: 0.15rem 0;
    border: none;
    background: none;
    color: var(--muted);
    font-size: 0.9rem;
    font-weight: 600;
    letter-spacing: 0.02em;
  }

  .utility-nav__menu-toggle::after {
    content: "";
    inline-size: 0.46rem;
    block-size: 0.46rem;
    border-right: 2px solid currentColor;
    border-bottom: 2px solid currentColor;
    transform: translateY(-0.08rem) rotate(45deg);
    transition: transform 180ms ease;
  }

  .utility-nav__links--interactive {
    display: none;
    position: absolute;
    inset-inline-start: 0;
    inset-inline-end: 0;
    top: calc(100% + 0.4rem);
    z-index: 40;
    min-inline-size: 0;
    padding: 0.45rem;
    border: 1px solid rgba(72, 84, 95, 0.14);
    border-radius: 1rem;
    background: rgba(249, 247, 243, 0.97);
    box-shadow: 0 18px 34px rgba(19, 26, 33, 0.18);
    backdrop-filter: blur(16px);
    flex-direction: column;
    gap: 0.1rem;
  }

  .utility-nav__links--interactive.is-open {
    display: flex;
  }

  .utility-nav__menu-toggle[aria-expanded="true"]::after {
    transform: translateY(0.1rem) rotate(-135deg);
  }

  .utility-nav__links--interactive a {
    padding: 0.55rem 0.35rem;
  }

  .utility-nav__links--interactive .nav-link--mobile-secondary {
    display: none;
  }

  .utility-nav .site-language--interactive .site-language__link {
    width: 100%;
    min-inline-size: 0;
    justify-content: flex-start;
    white-space: normal;
  }

  .utility-nav__links {
    font-size: 0.92rem;
  }

  .main {
    padding: 1rem 0.8rem 3rem;
  }

  .sidebar {
    display: none;
  }

  .mobile-endmatter {
    display: grid;
    gap: 1.25rem;
    margin: 2rem 0 0;
  }

  .mobile-endmatter .toc > li:last-child {
    margin-bottom: 0;
  }

  .sidebar {
    padding: 1.25rem 1rem;
  }

  .title-page,
  .copyright-page,
  .dedication-page,
  .subchapter {
    padding: 1.35rem 1.1rem;
  }

  .chapter-header {
    padding: 2rem 1rem 1.4rem;
  }
}