/* ==========================================================================
   nav.css — fixed glass bar, sliding scrollspy pill, tools, progress hairline,
   mobile full-screen menu.  Markup is rendered by nav.js into #site-nav.
   ========================================================================== */

.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: var(--z-nav);
  height: var(--nav-h);
}

/* ---------------------------------------------------------------- the bar */
.nav__bar {
  position: relative;
  z-index: 1;
  height: 100%;
  border-bottom: 1px solid transparent;
  background: transparent;
  background: color-mix(in srgb, var(--bg) 26%, transparent);
  -webkit-backdrop-filter: blur(12px) saturate(140%);
  backdrop-filter: blur(12px) saturate(140%);
  transition: background-color 0.45s var(--ease), border-color 0.45s var(--ease), transform 0.6s var(--ease-out),
    box-shadow 0.45s var(--ease);
}
.nav.is-scrolled .nav__bar {
  background: var(--veil);
  background: color-mix(in srgb, var(--bg) 76%, transparent);
  border-bottom-color: var(--line);
  box-shadow: var(--shadow-lg);
}
.nav.is-hidden .nav__bar {
  transform: translate3d(0, -101%, 0);
}
.nav.is-menu-open .nav__bar {
  background: transparent;
  border-bottom-color: transparent;
  box-shadow: none;
  -webkit-backdrop-filter: none;
  backdrop-filter: none;
}

.nav__inner {
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  gap: var(--s-4);
  height: 100%;
  max-width: calc(var(--container) + var(--gutter) * 2);
  margin-inline: auto;
  padding-inline: var(--gutter);
}

/* entrance (fill-mode: backwards only, so .is-hidden's transform is never overridden) */
html.js .nav.is-mounted .nav__bar {
  animation: nav-drop 0.9s var(--ease-out) backwards;
}
html.js .nav.is-mounted .nav__logo,
html.js .nav.is-mounted .nav__links .nav__link,
html.js .nav.is-mounted .nav__tools > * {
  animation: nav-in 0.8s var(--ease-out) backwards;
  animation-delay: calc(0.18s + var(--i, 0) * 55ms);
}
html.js .nav.is-mounted .nav__tools > :nth-child(2) { --i: 6; }
html.js .nav.is-mounted .nav__tools > :nth-child(3) { --i: 7; }
html.js .nav.is-mounted .nav__tools > :nth-child(1) { --i: 5; }
@keyframes nav-drop {
  from {
    opacity: 0;
    transform: translate3d(0, -100%, 0);
  }
}
@keyframes nav-in {
  from {
    opacity: 0;
    transform: translate3d(0, -8px, 0);
  }
}

/* ------------------------------------------------------- progress hairline */
.nav__progress {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  z-index: 3;
  height: 2px;
  pointer-events: none;
}
.nav__progress-bar {
  display: block;
  width: 100%;
  height: 100%;
  background: var(--accent-grad);
  box-shadow: 0 0 14px rgba(var(--accent-rgb), 0.7);
  transform-origin: 0 50%;
  transform: scaleX(var(--p, 0));
  opacity: 0;
  transition: opacity 0.3s var(--ease);
}
.nav__progress.is-on .nav__progress-bar {
  opacity: 1;
}

/* ------------------------------------------------------------------- logo */
.nav__logo {
  display: inline-flex;
  align-items: center;
  gap: 12px;
  padding: 4px 6px 4px 2px;
  margin-left: -2px;
  border-radius: var(--r-sm);
}
.nav__mark {
  position: relative;
  display: grid;
  place-items: center;
  flex: none;
  width: 36px;
  height: 36px;
  background: rgba(var(--accent-rgb), 0.06);
  color: var(--accent);
  transition: background-color var(--dur-2), box-shadow var(--dur-3);
}
/* viewfinder corners */
.nav__mark::before {
  content: "";
  position: absolute;
  inset: 0;
  pointer-events: none;
  transition: inset var(--dur-3) var(--ease-out);
  background:
    linear-gradient(var(--accent), var(--accent)) top left / 9px 1.5px no-repeat,
    linear-gradient(var(--accent), var(--accent)) top left / 1.5px 9px no-repeat,
    linear-gradient(var(--accent), var(--accent)) top right / 9px 1.5px no-repeat,
    linear-gradient(var(--accent), var(--accent)) top right / 1.5px 9px no-repeat,
    linear-gradient(var(--accent), var(--accent)) bottom left / 9px 1.5px no-repeat,
    linear-gradient(var(--accent), var(--accent)) bottom left / 1.5px 9px no-repeat,
    linear-gradient(var(--accent), var(--accent)) bottom right / 9px 1.5px no-repeat,
    linear-gradient(var(--accent), var(--accent)) bottom right / 1.5px 9px no-repeat;
}
.nav__mark-txt {
  font-family: var(--font-sans);
  font-size: 1.2rem;
  font-weight: 700;
  line-height: 1;
  letter-spacing: 0;
  background: var(--accent-grad);
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
  -webkit-text-fill-color: transparent;
  filter: drop-shadow(0 0 8px rgba(var(--accent-rgb), 0.45));
}
.nav__word {
  font-size: 0.95rem;
  font-weight: 600;
  letter-spacing: -0.02em;
  white-space: nowrap;
  color: var(--text);
}
.nav__word::after {
  content: "";
  display: inline-block;
  width: 0.5em;
  height: 1em;
  margin-left: 0.22em;
  vertical-align: -0.14em;
  background: var(--accent);
  opacity: 0;
}
@media (hover: hover) and (pointer: fine) {
  .nav__logo:hover .nav__mark::before {
    inset: -3px;
  }
  .nav__logo:hover .nav__mark {
    background: rgba(var(--accent-rgb), 0.12);
  }
  .nav__logo:hover .nav__word::after {
    opacity: 1;
    animation: caret-blink 1.05s steps(1) infinite;
  }
}
.nav__logo:focus-visible {
  border-radius: var(--r-sm);
}

/* ------------------------------------------------- section links + indicators */
.nav__links {
  justify-self: center;
  min-width: 0;
}
.nav__track {
  position: relative;
  display: inline-block;
}
.nav__list {
  display: flex;
  align-items: center;
  gap: 2px;
}
.nav__item {
  display: block;
}
.nav__link {
  position: relative;
  z-index: 1;
  display: inline-flex;
  align-items: center;
  gap: 7px;
  height: 36px;
  padding: 0 13px;
  border-radius: var(--r-pill);
  color: var(--text-2);
  font-size: 0.8125rem;
  font-weight: 500;
  letter-spacing: 0.005em;
  white-space: nowrap;
  transition: color 0.25s var(--ease);
}
.nav__link.is-active {
  color: var(--text);
}
@media (hover: hover) and (pointer: fine) {
  .nav__link:hover {
    color: var(--text);
  }
}
.nav__idx {
  color: var(--text-3);
  font-size: var(--fs-micro);
  letter-spacing: 0.04em;
  transition: color 0.3s var(--ease);
}
.nav__link.is-active .nav__idx {
  color: var(--accent);
}
@media (hover: hover) and (pointer: fine) {
  .nav__link:hover .nav__idx {
    color: var(--accent);
  }
}
:root[data-lang="zh"] .nav__label {
  letter-spacing: 0.04em;
}

.nav__pill,
.nav__ghost {
  position: absolute;
  left: 0;
  top: 50%;
  width: var(--w, 0px);
  height: var(--h, 36px);
  border-radius: var(--r-pill);
  opacity: 0;
  pointer-events: none;
  transform: translate3d(var(--x, 0px), -50%, 0);
  transition: transform 0.55s var(--ease-out), width 0.55s var(--ease-out), height 0.3s var(--ease), opacity 0.3s var(--ease);
}
.nav__pill.is-on,
.nav__ghost.is-on {
  opacity: 1;
}
.nav__pill.no-anim,
.nav__ghost.no-anim {
  transition: opacity 0.3s var(--ease);
}
.nav__pill {
  background: rgba(var(--accent-rgb), 0.09);
  border: 1px solid rgba(var(--accent-rgb), 0.24);
}
.nav__pill::after {
  content: "";
  position: absolute;
  left: 24%;
  right: 24%;
  bottom: -1px;
  height: 2px;
  border-radius: 2px;
  background: var(--accent-grad);
  box-shadow: 0 0 12px rgba(var(--accent-rgb), 0.85);
}
.nav__ghost {
  background: var(--line);
  background: color-mix(in srgb, var(--text) 7%, transparent);
}

/* ------------------------------------------------------------------ tools */
.nav__tools {
  display: flex;
  align-items: center;
  gap: 8px;
}
.nav__cmdk {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  height: 36px;
  padding: 0 8px 0 12px;
  border: 1px solid var(--line);
  border-radius: var(--r-pill);
  background: rgba(var(--accent-rgb), 0.02);
  color: var(--text-2);
  font-size: 0.8125rem;
  transition: color var(--dur-1), border-color var(--dur-2), background-color var(--dur-2);
}
@media (hover: hover) and (pointer: fine) {
  .nav__cmdk:hover {
    border-color: var(--line-accent);
    background: rgba(var(--accent-rgb), 0.07);
    color: var(--text);
  }
}
.nav__cmdk-ico {
  display: inline-flex;
}
.nav__cmdk-ico .icon {
  width: 15px;
  height: 15px;
}
.nav__cmdk-text {
  min-width: 4.4em;
  text-align: left;
}
.nav__cmdk .kbd {
  margin-left: 2px;
}

.nav__lang {
  position: relative;
  display: inline-grid;
  grid-template-columns: 1fr 1fr;
  height: 36px;
  padding: 3px;
  border: 1px solid var(--line);
  border-radius: var(--r-pill);
}
.nav__lang-thumb {
  position: absolute;
  top: 3px;
  bottom: 3px;
  left: 3px;
  width: calc((100% - 6px) / 2);
  border-radius: var(--r-pill);
  background: rgba(var(--accent-rgb), 0.14);
  box-shadow: inset 0 0 0 1px rgba(var(--accent-rgb), 0.38);
  transition: transform 0.45s var(--ease-out);
}
.nav__lang[data-active="zh"] .nav__lang-thumb {
  transform: translateX(100%);
}
.nav__lang-btn {
  position: relative;
  z-index: 1;
  min-width: 34px;
  padding: 0 9px;
  border-radius: var(--r-pill);
  color: var(--text-3);
  font-size: var(--fs-micro);
  font-weight: 600;
  letter-spacing: 0.04em;
  transition: color var(--dur-2);
}
@media (hover: hover) and (pointer: fine) {
  .nav__lang-btn:hover {
    color: var(--text);
  }
}
.nav__lang-btn[aria-pressed="true"] {
  color: var(--accent);
}

.nav__theme {
  position: relative;
  flex: none;
  width: 36px;
  height: 36px;
  border: 1px solid var(--line);
  border-radius: 50%;
  color: var(--text-2);
  transition: color var(--dur-2), border-color var(--dur-2), background-color var(--dur-2);
}
@media (hover: hover) and (pointer: fine) {
  .nav__theme:hover {
    border-color: var(--line-accent);
    background: rgba(var(--accent-rgb), 0.07);
    color: var(--accent);
  }
}
.nav__theme-ico {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
  transition: transform 0.65s var(--ease-out), opacity 0.35s var(--ease);
}
.nav__theme-ico .icon {
  width: 17px;
  height: 17px;
}
/* morph: the icon of the ACTIVE theme is shown; the other one spins away */
html[data-theme="dark"] .nav__theme-sun {
  opacity: 0;
  transform: rotate(-90deg) scale(0.35);
}
html[data-theme="light"] .nav__theme-moon {
  opacity: 0;
  transform: rotate(90deg) scale(0.35);
}

/* ----------------------------------------------------------------- burger */
.nav__burger {
  display: none;
  position: relative;
  width: 44px;
  height: 44px;
  margin-right: -10px;
  border-radius: 50%;
}
.nav__burger-box {
  position: absolute;
  left: 50%;
  top: 50%;
  width: 22px;
  height: 11px;
  transform: translate(-50%, -50%);
}
.nav__burger-box i {
  position: absolute;
  left: 0;
  right: 0;
  height: 1.5px;
  border-radius: 2px;
  background: var(--text);
  transition: transform 0.5s var(--ease-out), top 0.35s var(--ease-out);
}
.nav__burger-box i:nth-child(1) {
  top: 0;
}
.nav__burger-box i:nth-child(2) {
  top: calc(100% - 1.5px);
}
.nav.is-menu-open .nav__burger-box i:nth-child(1) {
  top: calc(50% - 0.75px);
  transform: rotate(45deg);
}
.nav.is-menu-open .nav__burger-box i:nth-child(2) {
  top: calc(50% - 0.75px);
  transform: rotate(-45deg);
}

/* ------------------------------------------------------------ mobile menu */
.nav__menu {
  position: fixed;
  inset: 0;
  z-index: 0;
  display: none;
  flex-direction: column;
  padding: calc(var(--nav-h) + 12px) var(--gutter) max(28px, env(safe-area-inset-bottom));
  overflow-y: auto;
  overscroll-behavior: contain;
  background: var(--panel-solid);
  background: color-mix(in srgb, var(--bg) 90%, transparent);
  -webkit-backdrop-filter: blur(28px) saturate(150%);
  backdrop-filter: blur(28px) saturate(150%);
  visibility: hidden;
  opacity: 0;
  transition: opacity 0.4s var(--ease), visibility 0s linear 0.4s;
}
.nav.is-menu-open .nav__menu {
  visibility: visible;
  opacity: 1;
  transition-delay: 0s;
}
.nav__menu::before {
  /* faint scanline grid — echoes the terminal / viewfinder motif */
  content: "";
  position: absolute;
  inset: 0;
  z-index: -1;
  pointer-events: none;
  opacity: 0.5;
  background:
    linear-gradient(var(--line), var(--line)) 0 0 / 1px 100% no-repeat,
    radial-gradient(600px circle at 100% 0%, rgba(var(--accent-rgb), 0.1), transparent 60%),
    radial-gradient(500px circle at 0% 100%, rgba(var(--accent-2-rgb), 0.1), transparent 60%);
}
.nav__menu-nav .nav__list {
  display: block;
  border-top: 1px solid var(--line);
}
.nav__menu .nav__link {
  display: grid;
  grid-template-columns: 2.4rem minmax(0, 1fr) auto;
  align-items: baseline;
  gap: 14px;
  width: 100%;
  height: auto;
  padding: clamp(11px, 2.3vh, 18px) 0;
  border-bottom: 1px solid var(--line);
  border-radius: 0;
  color: var(--text);
  font-size: clamp(1.9rem, 8.4vw, 2.7rem);
  font-weight: 600;
  line-height: 1.1;
  letter-spacing: var(--tracking-tight);
  opacity: 0;
  transform: translate3d(0, 26px, 0);
  transition: opacity 0.35s var(--ease), transform 0.5s var(--ease-out), color var(--dur-2);
}
.nav.is-menu-open .nav__menu .nav__link {
  opacity: 1;
  transform: none;
  transition: opacity 0.6s var(--ease-out), transform 0.8s var(--ease-out), color var(--dur-2);
  transition-delay: calc(90ms + var(--i, 0) * 55ms), calc(90ms + var(--i, 0) * 55ms), 0s;
}
.nav__menu .nav__idx {
  font-size: var(--fs-micro);
  letter-spacing: 0.08em;
}
.nav__menu .nav__link.is-active {
  color: var(--accent);
}
.nav__arrow {
  display: inline-flex;
  align-self: center;
  color: var(--text-3);
  opacity: 0.6;
  transform: translateX(-6px);
  transition: transform var(--dur-3) var(--ease-out), color var(--dur-2), opacity var(--dur-2);
}
.nav__arrow .icon {
  width: 22px;
  height: 22px;
}
.nav__menu .nav__link.is-active .nav__arrow {
  color: var(--accent);
  opacity: 1;
  transform: none;
}
/* current-section marker: a 6px dot left of the arrow (space is always reserved, so rows never jump) */
.nav__menu .nav__arrow {
  align-items: center;
  gap: 10px;
}
.nav__menu .nav__arrow::before {
  content: "";
  flex: none;
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--accent);
  box-shadow: 0 0 10px rgba(var(--accent-rgb), 0.55);
  opacity: 0;
  transform: scale(0.4);
  transition: opacity var(--dur-2), transform var(--dur-3) var(--ease-out);
}
.nav__menu .nav__link.is-active .nav__arrow::before {
  opacity: 1;
  transform: none;
}

.nav__menu-tools {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 12px;
  margin-top: auto;
  padding-top: 28px;
  opacity: 0;
  transform: translate3d(0, 18px, 0);
  transition: opacity 0.3s var(--ease), transform 0.4s var(--ease-out);
}
.nav.is-menu-open .nav__menu-tools {
  opacity: 1;
  transform: none;
  transition: opacity 0.6s var(--ease-out) 0.5s, transform 0.8s var(--ease-out) 0.5s;
}
.nav__menu-cmdk {
  flex: 1 1 100%;
  height: 52px;
  padding: 0 14px;
  font-size: 0.95rem;
}
.nav__menu-cmdk .nav__cmdk-text {
  flex: 1;
}
.nav__menu-cmdk .kbd {
  margin-left: auto;
}
.nav__menu-lang,
.nav__menu-theme {
  height: 52px;
}
.nav__menu-lang {
  flex: 1 1 auto;
}
.nav__menu-lang .nav__lang-btn {
  min-width: 56px;
  min-height: var(--tap);
  font-size: 0.8rem;
}
.nav__menu-theme {
  width: 52px;
}
.nav__menu-meta {
  margin-top: 22px;
  color: var(--text-3);
  font-size: var(--fs-xs);
  letter-spacing: 0.06em;
  opacity: 0;
  transition: opacity 0.3s var(--ease);
}
.nav.is-menu-open .nav__menu-meta {
  opacity: 1;
  transition: opacity 0.8s var(--ease-out) 0.65s;
}

/* -------------------------------------------------------------- responsive
   Breakpoints are in em (= the browser's default font size, not the page's), so a larger
   default font switches to the compact / mobile layouts earlier instead of colliding. */
@media (max-width: 59.99em) {
  .nav__inner {
    grid-template-columns: 1fr auto;
  }
  .nav__links,
  .nav__tools > :not(.nav__burger) {
    display: none;
  }
  .nav__burger {
    display: block;
  }
  .nav__menu {
    display: flex;
  }
}
@media (min-width: 60em) and (max-width: 67.49em) {
  .nav__word,
  .nav__idx {
    display: none;
  }
  .nav__link {
    padding: 0 11px;
  }
}
@media (min-width: 60em) and (max-width: 73.74em) {
  .nav__tool .nav__cmdk-text {
    display: none;
  }
  .nav__cmdk.nav__tool {
    padding: 0 8px 0 11px;
  }
}
@media (min-width: 60em) and (max-width: 73.74em) and (pointer: coarse) {
  .nav__cmdk.nav__tool {
    min-width: var(--tap);
    justify-content: center;
    padding: 0 10px;
  }
}
@media (hover: none) {
  .nav__cmdk-kbd {
    display: none;
  }
}
/* touch-sized controls on coarse pointers (hybrid / tablet widths) */
@media (pointer: coarse) {
  .nav__cmdk,
  .nav__link {
    height: var(--tap);
  }
  .nav__lang {
    height: 52px; /* 44px buttons + 3px padding + 1px border */
  }
  .nav__lang-btn {
    min-width: var(--tap);
    min-height: var(--tap);
  }
  .nav__theme {
    width: var(--tap);
    height: var(--tap);
  }
}

/* fade at the bottom edge while the mobile menu still has content below the fold (takes no layout space) */
.nav__menu::after {
  content: "";
  display: none;
  flex: none;
  grid-column: 1 / -1;
  position: sticky;
  bottom: calc(-1 * max(28px, env(safe-area-inset-bottom)));
  height: 56px;
  margin: -56px calc(-1 * var(--gutter)) 0;
  pointer-events: none;
  background: linear-gradient(to bottom, transparent, var(--bg));
}
.nav__menu.has-more::after {
  display: block;
}

/* landscape phones: the menu is short, so the links and the tools sit side by side and every row stays tappable */
@media (max-width: 59.99em) and (max-height: 500px) and (orientation: landscape) {
  .nav__menu {
    display: grid;
    grid-template-columns: minmax(0, 1.35fr) minmax(0, 1fr);
    grid-template-rows: auto 1fr;
    column-gap: clamp(20px, 5vw, 48px);
    align-content: start;
    padding-top: calc(var(--nav-h) + 4px);
    padding-bottom: max(16px, env(safe-area-inset-bottom));
  }
  .nav__menu-nav {
    grid-column: 1;
    grid-row: 1 / span 2;
  }
  .nav__menu .nav__link {
    padding: 0;
    min-height: var(--tap);
    align-items: center;
    font-size: clamp(1.15rem, 3.6vh, 1.5rem);
  }
  .nav__menu .nav__arrow .icon {
    width: 18px;
    height: 18px;
  }
  .nav__menu-tools {
    grid-column: 2;
    grid-row: 1;
    margin-top: 0;
    padding-top: 0;
    align-content: start;
  }
  .nav__menu-cmdk {
    height: var(--tap);
  }
  .nav__menu-meta {
    grid-column: 2;
    grid-row: 2;
    align-self: end;
    margin-top: 14px;
  }
}

/* ------------------------------------------- theme switch: circular reveal */
html.theme-vt::view-transition-old(root),
html.theme-vt::view-transition-new(root) {
  animation: none;
  mix-blend-mode: normal;
}
html.theme-vt::view-transition-old(root) {
  z-index: 1;
}
html.theme-vt::view-transition-new(root) {
  z-index: 2;
}


/* --------------------------------------------------------------------------
   Calm dark — dark theme only (the light theme keeps the rules above untouched):
   one soft accent, no glow on the progress line, the active underline or the G mark.
   -------------------------------------------------------------------------- */
:root:not([data-theme="light"]) .nav__progress-bar {
  background: var(--accent);
  box-shadow: none;
}
:root:not([data-theme="light"]) .nav__pill::after {
  background: var(--accent);
  box-shadow: none;
}
:root:not([data-theme="light"]) .nav__mark-txt {
  filter: none;
}
:root:not([data-theme="light"]) .nav__menu::before {
  background: linear-gradient(var(--line), var(--line)) 0 0 / 1px 100% no-repeat;
}
:root:not([data-theme="light"]) .nav__menu .nav__arrow::before {
  box-shadow: none;
}