/* ============================================================================
   nav.css — sticky navigation, scroll progress, chapter badge
   ========================================================================== */

.site-nav {
  position: fixed;
  inset-block-start: 0;
  inset-inline: 0;
  z-index: 100;
  height: var(--nav-h);
  display: flex;
  align-items: center;
  transition: background-color 0.4s var(--ease-out-power3),
              border-color 0.4s var(--ease-out-power3),
              color 0.4s var(--ease-out-power3);
  border-bottom: 1px solid transparent;
}

/* Over a navy chapter the bar is light-on-dark; over a light chapter it flips.
   data-on is set from the chapter currently under the bar. */
.site-nav[data-on="navy"] {
  color: var(--white);
  --nav-fg: var(--white);
  --nav-muted: rgba(255, 255, 255, 0.62);
  --nav-line: rgba(255, 255, 255, 0.16);
  --nav-veil: rgba(0, 10, 64, 0.9);
}

.site-nav[data-on="light"] {
  color: var(--navy-900);
  --nav-fg: var(--navy-900);
  --nav-muted: var(--slate-500);
  --nav-line: var(--slate-200);
  --nav-veil: rgba(255, 255, 255, 0.92);
}

.site-nav.is-stuck {
  background: var(--nav-veil);
  backdrop-filter: blur(14px) saturate(160%);
  -webkit-backdrop-filter: blur(14px) saturate(160%);
  border-bottom-color: var(--nav-line);
}

.site-nav__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-6);
  width: 100%;
}

/* -- Logo ----------------------------------------------------------------- */

.nav-logo {
  display: inline-flex;
  align-items: center;
  gap: var(--space-3);
  flex: none;
}

.nav-logo__mark {
  width: 28px;
  height: 28px;
  flex: none;
}

.nav-logo__word {
  font-family: var(--font-sans);
  font-size: 19px;
  font-weight: var(--weight-extrabold);
  letter-spacing: -0.02em;
  color: var(--nav-fg);
}

/* -- Links ---------------------------------------------------------------- */

.nav-links {
  display: none;
  align-items: center;
  gap: var(--space-1);
}

/* Seven links need ~810px; below 1280 they would push the actions off the
   bar, so the burger panel covers everything narrower. */
@media (min-width: 1280px) {
  .nav-links { display: flex; }
}

.nav-link {
  position: relative;
  padding: 8px 12px;
  font-family: var(--font-sans);
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
  color: var(--nav-muted);
  cursor: pointer;
  transition: color var(--dur-base) ease;
  white-space: nowrap;
}

.nav-link::after {
  content: "";
  position: absolute;
  left: 12px;
  right: 12px;
  bottom: 2px;
  height: 3px;
  background: var(--yellow-500);
  border-radius: 2px;
  transform: scaleX(0);
  transform-origin: left;
  transition: transform var(--dur-base) var(--ease-out-power3);
}

@media (min-width: 1280px) and (max-width: 1439px) {
  .nav-link { padding-inline: 9px; font-size: 13px; }
  .nav-link::after { left: 9px; right: 9px; }
}

.nav-link:hover { color: var(--nav-fg); }
.nav-link:hover::after,
.nav-link[aria-current="true"]::after { transform: scaleX(1); }
.nav-link[aria-current="true"] { color: var(--nav-fg); font-weight: var(--weight-bold); }

/* -- Right cluster -------------------------------------------------------- */

.nav-actions {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  flex: none;
}

.lang-toggle {
  display: inline-flex;
  align-items: center;
  border: 1px solid var(--nav-line);
  border-radius: var(--radius-full);
  padding: 2px;
}

.lang-toggle button {
  padding: 5px 12px;
  border-radius: var(--radius-full);
  font-family: var(--font-mono);
  font-size: 11px;
  font-weight: var(--weight-semibold);
  letter-spacing: 0.06em;
  color: var(--nav-muted);
  cursor: pointer;
  transition: background-color var(--dur-base) ease, color var(--dur-base) ease;
}

.lang-toggle button[aria-pressed="true"] {
  background: var(--yellow-500);
  color: var(--navy-900);
}

.nav-cta { display: none; }

@media (min-width: 640px) {
  .nav-cta { display: inline-flex; }
}

/* -- Mobile menu ---------------------------------------------------------- */

.nav-burger {
  display: inline-flex;
  flex-direction: column;
  justify-content: center;
  gap: 5px;
  width: 40px;
  height: 40px;
  padding: 0 9px;
  border-radius: var(--radius-sm);
  cursor: pointer;
}

@media (min-width: 1280px) {
  .nav-burger { display: none; }
}

.nav-burger span {
  display: block;
  height: 2px;
  background: var(--nav-fg);
  border-radius: 2px;
  transition: transform var(--dur-base) var(--ease-out-power3),
              opacity var(--dur-fast) ease;
}

.nav-burger[aria-expanded="true"] span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.nav-burger[aria-expanded="true"] span:nth-child(2) { opacity: 0; }
.nav-burger[aria-expanded="true"] span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

.nav-panel {
  position: fixed;
  inset-block-start: var(--nav-h);
  inset-inline: 0;
  z-index: 99;
  padding: var(--space-6) var(--gutter-sm) var(--space-10);
  background: var(--navy-900);
  color: var(--white);
  border-bottom: 1px solid rgba(255, 255, 255, 0.14);
  display: flex;
  flex-direction: column;
  gap: var(--space-1);
  transform: translateY(-8px);
  opacity: 0;
  pointer-events: none;
  transition: transform var(--dur-base) var(--ease-out-power3),
              opacity var(--dur-base) ease;
}

.nav-panel.is-open {
  transform: translateY(0);
  opacity: 1;
  pointer-events: auto;
}

@media (min-width: 1280px) {
  .nav-panel { display: none; }
}

.nav-panel a {
  display: flex;
  align-items: baseline;
  gap: var(--space-4);
  padding: 14px 4px;
  border-bottom: 1px solid rgba(255, 255, 255, 0.08);
  font-family: var(--font-sans);
  font-size: var(--text-lg);
  font-weight: var(--weight-semibold);
}

/* Only the leading chapter number is mono/yellow; the label stays as-is. */
.nav-panel a span:first-child {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  color: var(--yellow-500);
}

/* -- Scroll progress ------------------------------------------------------ */

.scroll-progress {
  position: fixed;
  inset-block-start: 0;
  inset-inline: 0;
  z-index: 101;
  height: 3px;
  background: var(--yellow-500);
  transform: scaleX(0);
  transform-origin: left;
  will-change: transform;
}

/* -- Chapter badge -------------------------------------------------------- */

.chapter-badge {
  position: fixed;
  inset-block-end: 24px;
  inset-inline-start: 24px;
  z-index: 90;
  display: none;
  align-items: center;
  gap: var(--space-2);
  padding: 8px 14px;
  border-radius: var(--radius-full);
  background: rgba(0, 10, 64, 0.82);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  border: 1px solid rgba(255, 255, 255, 0.16);
  font-family: var(--font-mono);
  font-size: 11px;
  font-weight: var(--weight-semibold);
  letter-spacing: 0.1em;
  color: var(--white);
  opacity: 0;
  transition: opacity var(--dur-base) ease;
}

.chapter-badge.is-visible { opacity: 1; }

.chapter-badge__dot {
  width: 6px;
  height: 6px;
  border-radius: var(--radius-full);
  background: var(--yellow-500);
  flex: none;
}

@media (min-width: 1024px) {
  .chapter-badge { display: inline-flex; }
}