.rt-book-nav {
  display: inline-flex;
  align-items: center;
  gap: 0.55rem;
  margin-right: 0.7rem;
}

.rt-lang-switcher {
  display: inline-flex;
  align-items: stretch;
  border: 1px solid var(--theme-popup-border);
  border-radius: 999px;
  overflow: hidden;
  background: color-mix(in srgb, var(--theme-popup-bg) 92%, transparent);
  box-shadow: 0 10px 24px rgba(0, 0, 0, 0.08);
}

.rt-nav-pill,
.rt-book-menu > summary {
  min-height: 2rem;
  border: 0;
  color: var(--fg);
  background: transparent;
  text-decoration: none;
  cursor: pointer;
  font-size: 0.8rem;
  line-height: 1;
  font-weight: 700;
  letter-spacing: 0.01em;
}

.rt-nav-pill {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0 0.82rem;
}

.rt-nav-pill + .rt-nav-pill {
  border-left: 1px solid color-mix(in srgb, var(--theme-popup-border) 72%, transparent);
}

.rt-nav-pill:hover,
.rt-nav-pill:focus-visible,
.rt-book-menu > summary:hover,
.rt-book-menu > summary:focus-visible,
.rt-book-link:hover,
.rt-book-link:focus-visible {
  background: var(--theme-hover);
}

.rt-nav-pill.is-active {
  background: var(--sidebar-active);
  color: var(--bg);
  cursor: default;
  pointer-events: none;
}

.rt-book-menu {
  position: relative;
}

.rt-book-menu > summary {
  list-style: none;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.42rem;
  padding: 0 0.88rem;
  border: 1px solid var(--theme-popup-border);
  border-radius: 999px;
  background: color-mix(in srgb, var(--theme-popup-bg) 92%, transparent);
  user-select: none;
  box-shadow: 0 10px 24px rgba(0, 0, 0, 0.08);
}

.rt-book-menu > summary::-webkit-details-marker {
  display: none;
}

.rt-book-menu[open] > summary {
  background: var(--theme-hover);
}

.rt-book-menu-popup {
  position: absolute;
  top: calc(100% + 0.5rem);
  right: 0;
  z-index: 1000;
  width: min(24rem, 76vw);
  padding: 0.5rem;
  border: 1px solid var(--theme-popup-border);
  border-radius: 16px;
  background: color-mix(in srgb, var(--theme-popup-bg) 96%, transparent);
  box-shadow: 0 22px 44px rgba(0, 0, 0, 0.22);
  backdrop-filter: blur(10px);
}

.rt-book-menu-label {
  display: block;
  margin: 0.15rem 0.35rem 0.5rem;
  color: var(--sidebar-fg);
  font-size: 0.72rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.rt-book-list {
  display: grid;
  gap: 0.28rem;
}

.rt-book-link {
  display: block;
  padding: 0.72rem 0.82rem;
  border-radius: 12px;
  text-decoration: none;
  transition: background 0.15s ease, transform 0.15s ease;
}

.rt-book-link:hover,
.rt-book-link:focus-visible {
  transform: translateY(-1px);
}

.rt-book-link-main {
  display: block;
  color: var(--fg);
  font-size: 0.88rem;
  font-weight: 700;
  line-height: 1.3;
}

.rt-book-link-sub {
  display: block;
  margin-top: 0.18rem;
  color: var(--sidebar-fg);
  font-size: 0.76rem;
  line-height: 1.35;
  opacity: 0.88;
}

.rt-book-menu-caret {
  font-size: 0.72rem;
  opacity: 0.82;
}

.rust .rt-lang-switcher,
.rust .rt-book-menu > summary {
  border-color: color-mix(in srgb, var(--theme-popup-border) 72%, #6a4d3c 28%);
  background: color-mix(in srgb, var(--theme-popup-bg) 82%, #f2e7dc 18%);
}

.rust .rt-book-menu-popup {
  background: color-mix(in srgb, var(--theme-popup-bg) 90%, #f6efe6 10%);
}

@media (max-width: 980px) {
  .rt-book-nav {
    gap: 0.42rem;
    margin-right: 0.45rem;
  }

  .rt-nav-pill,
  .rt-book-menu > summary {
    min-height: 1.9rem;
    padding-left: 0.72rem;
    padding-right: 0.72rem;
    font-size: 0.76rem;
  }

  .rt-book-menu-popup {
    width: min(21rem, 82vw);
  }
}

@media (max-width: 720px) {
  .rt-book-nav {
    width: 100%;
    justify-content: flex-end;
    margin-right: 0;
    margin-top: 0.35rem;
  }

  .menu-bar .right-buttons {
    flex-wrap: wrap;
    row-gap: 0.35rem;
  }

  .rt-book-menu-popup {
    right: 0;
    width: min(19rem, 88vw);
  }
}