:root {
  --chapter-sticky-offset: 0px;
  --chapter-nav-height: 0px;
  --chapter-anchor-offset: 96px;
  --chapter-accent: var(--accent, #3f6654);
  --chapter-ink: var(--ink, #1f2d26);
  --chapter-muted: var(--muted, #68766f);
  --chapter-line: var(--line, rgba(63, 102, 84, 0.2));
  --chapter-panel: var(--panel, rgba(255, 255, 255, 0.96));
  --chapter-shadow: var(--shadow, 0 14px 36px rgba(31, 45, 38, 0.12));
}

[data-chapter-id] {
  scroll-margin-top: var(--chapter-anchor-offset, 96px);
}

.chapter-menu {
  position: sticky;
  top: var(--chapter-sticky-offset, 0px);
  z-index: 40;
  width: min(1120px, calc(100% - 32px));
  margin: 0 auto;
  padding: 10px 0;
}

.chapter-toggle {
  width: min(340px, 100%);
  min-height: 44px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  padding: 10px 12px;
  border: 1px solid color-mix(in srgb, var(--chapter-accent) 34%, transparent);
  border-radius: 10px;
  background: var(--chapter-panel);
  color: var(--chapter-ink);
  box-shadow: var(--chapter-shadow);
  font: inherit;
  cursor: pointer;
}

.chapter-toggle span {
  color: var(--chapter-muted);
  font-size: 13px;
  font-weight: 800;
}

.chapter-toggle strong {
  min-width: 0;
  overflow: hidden;
  color: var(--chapter-accent);
  font-size: 15px;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.chapter-toggle::after {
  content: "⌄";
  color: var(--chapter-accent);
  font-weight: 900;
}

.chapter-menu.open .chapter-toggle::after {
  content: "⌃";
}

.chapter-menu:not([data-chapter-mode="rail"]) .chapter-links {
  display: none;
  position: absolute;
  top: calc(100% - 8px);
  left: 0;
  width: min(340px, 100%);
  max-height: 58vh;
  overflow-y: auto;
  padding: 8px;
  border: 1px solid var(--chapter-line);
  border-radius: 10px;
  background: var(--chapter-panel);
  box-shadow: var(--chapter-shadow);
}

.chapter-menu:not([data-chapter-mode="rail"]).open .chapter-links {
  display: grid;
  gap: 4px;
}

.chapter-link {
  display: block;
  padding: 9px 10px;
  border-radius: 999px;
  color: var(--chapter-muted);
  text-decoration: none;
  font-weight: 800;
}

.chapter-link:hover,
.chapter-link.active {
  color: #fff;
  background: var(--chapter-accent);
}

.chapter-menu[data-chapter-mode="rail"] {
  width: 100%;
  padding: 9px max(16px, calc((100% - 1120px) / 2));
  border-block: 1px solid var(--chapter-line);
  background: color-mix(in srgb, var(--chapter-panel) 92%, transparent);
  box-shadow: 0 8px 26px rgba(31, 45, 38, 0.07);
  backdrop-filter: blur(14px);
}

.chapter-menu[data-chapter-mode="rail"] .chapter-current {
  display: flex;
  align-items: baseline;
  gap: 8px;
  margin-bottom: 7px;
  color: var(--chapter-muted);
  font-size: 12px;
  font-weight: 800;
}

.chapter-menu[data-chapter-mode="rail"] .chapter-current strong {
  min-width: 0;
  overflow: hidden;
  color: var(--chapter-accent);
  font-size: 14px;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.chapter-menu[data-chapter-mode="rail"] .chapter-links {
  position: static;
  display: flex;
  gap: 7px;
  width: 100%;
  overflow-x: auto;
  overflow-y: hidden;
  padding: 1px 0 5px;
  scroll-behavior: smooth;
  overscroll-behavior-inline: contain;
  scrollbar-width: none;
  -webkit-overflow-scrolling: touch;
}

.chapter-menu[data-chapter-mode="rail"] .chapter-links::-webkit-scrollbar {
  display: none;
}

.chapter-menu[data-chapter-mode="rail"] .chapter-link {
  flex: 0 0 auto;
  white-space: nowrap;
}

.chapter-dock {
  position: fixed;
  top: 50%;
  right: 18px;
  z-index: 45;
  display: flex;
  align-items: center;
  transform: translateY(-50%);
}

.chapter-dock-toggle {
  min-width: 46px;
  min-height: 46px;
  padding: 9px 10px;
  border: 1px solid var(--chapter-line);
  border-radius: 999px;
  background: var(--chapter-accent);
  color: #fff;
  box-shadow: var(--chapter-shadow);
  font: inherit;
  font-size: 13px;
  font-weight: 900;
  cursor: pointer;
  writing-mode: vertical-rl;
}

.chapter-dock-panel {
  width: min(290px, calc(100vw - 96px));
  max-height: min(70vh, 720px);
  margin-right: 8px;
  overflow-y: auto;
  padding: 10px;
  border: 1px solid var(--chapter-line);
  border-radius: 14px;
  background: var(--chapter-panel);
  box-shadow: var(--chapter-shadow);
  opacity: 0;
  pointer-events: none;
  transform: translateX(18px) scale(0.98);
  transition: opacity 160ms ease, transform 160ms ease;
}

.chapter-dock.is-open .chapter-dock-panel {
  opacity: 1;
  pointer-events: auto;
  transform: translateX(0) scale(1);
}

.chapter-dock-panel .chapter-link {
  border-radius: 9px;
}

@media (max-width: 1100px) {
  .chapter-dock {
    display: none;
  }
}

@media (max-width: 820px) {
  .chapter-menu[data-chapter-mode="rail"] {
    padding-inline: 12px;
  }

  .chapter-menu[data-chapter-mode="rail"] .chapter-current {
    margin-bottom: 5px;
  }

  .chapter-menu[data-chapter-mode="rail"] .chapter-link {
    padding: 8px 11px;
    font-size: 13px;
  }
}

@media (prefers-reduced-motion: reduce) {
  .chapter-menu[data-chapter-mode="rail"] .chapter-links {
    padding-inline: var(--chapter-edge-space, 0px);
    scroll-behavior: auto;
  }

  .chapter-dock-panel {
    transition: none;
  }
}