/* 小黑 product site
   Design read: calm premium consumer Android assistant, warm paper + ink + sparse star-blue.
   Dials: variance 7 / motion 4 / density 3.
   Accent locked to star-blue. Radius: 8px controls, 28px device only.
*/

:root {
  color-scheme: light dark;
  --paper: #f3ede3;
  --paper-2: #e8e0d2;
  --ink: #1b1e23;
  --ink-soft: #4e545c;
  --line: #c9c0b3;
  --star: #2e5f8c;
  --star-soft: #5a86ab;
  --on-star: #f3ede3;
  --shadow: color-mix(in srgb, #1b1e23 14%, transparent);
  --radius: 8px;
  --radius-device: 28px;
  --header-h: 4.25rem;
  --font: "PingFang SC", "Hiragino Sans GB", "Noto Sans SC", "Source Han Sans SC",
    "Microsoft YaHei UI", "Microsoft YaHei", system-ui, sans-serif;
  --ease: cubic-bezier(0.16, 1, 0.3, 1);
  --z-star: 0;
  --z-content: 1;
  --z-header: 10;
  --z-nav: 20;
}

@media (prefers-color-scheme: dark) {
  :root {
    --paper: #121820;
    --paper-2: #1a2330;
    --ink: #e6edf4;
    --ink-soft: #a8b4c0;
    --line: #2a3544;
    --star: #7eadd4;
    --star-soft: #5a8cb5;
    --on-star: #121820;
    --shadow: color-mix(in srgb, #000 38%, transparent);
  }
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  hanging-punctuation: first last;
  text-autospace: normal;
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  .site-nav,
  .btn,
  .faq-list summary::after {
    transition: none;
  }
}

body {
  margin: 0;
  min-width: 320px;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--font);
  font-size: 1.0625rem;
  line-height: 1.75;
  letter-spacing: 0.01em;
  overflow-wrap: break-word;
}

img,
svg {
  max-width: 100%;
  height: auto;
}

a {
  color: var(--star);
  text-decoration-thickness: 1px;
  text-underline-offset: 0.18em;
}

a:hover {
  color: var(--ink);
}

:focus {
  outline: none;
}

:focus-visible {
  outline: 2px solid var(--star);
  outline-offset: 3px;
}

.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.skip {
  position: absolute;
  left: 1rem;
  top: 0.75rem;
  z-index: calc(var(--z-nav) + 1);
  transform: translateY(-150%);
  background: var(--ink);
  color: var(--paper);
  padding: 0.6rem 0.9rem;
  border-radius: var(--radius);
  min-height: 44px;
}

.skip:focus {
  transform: none;
  color: var(--paper);
}

.wrap {
  width: min(72rem, calc(100% - 2rem));
  margin-inline: auto;
}

@media (min-width: 768px) {
  .wrap {
    width: min(72rem, calc(100% - 3rem));
  }
}

@media (min-width: 1440px) {
  .wrap {
    width: min(76rem, calc(100% - 5rem));
  }
}

.site-header {
  position: sticky;
  top: 0;
  z-index: var(--z-header);
  height: var(--header-h);
  background: color-mix(in srgb, var(--paper) 92%, transparent);
  border-bottom: 1px solid var(--line);
}

@supports (backdrop-filter: blur(12px)) {
  .site-header {
    backdrop-filter: blur(12px);
  }
}

@media (prefers-reduced-transparency: reduce) {
  .site-header {
    background: var(--paper);
    backdrop-filter: none;
  }
}

.header-inner {
  display: flex;
  align-items: center;
  gap: 1rem;
  height: var(--header-h);
}

.brand {
  display: inline-flex;
  align-items: baseline;
  gap: 0.55rem;
  color: var(--ink);
  text-decoration: none;
  min-height: 44px;
  padding-right: 0.25rem;
}

.brand:hover {
  color: var(--star);
}

.brand-mark {
  width: 36px;
  height: 36px;
  border-radius: 8px;
  align-self: center;
}

.brand-zh {
  font-size: 1.125rem;
  font-weight: 600;
  letter-spacing: 0.08em;
}

.brand-en {
  font-size: 0.82rem;
  color: var(--ink-soft);
  letter-spacing: 0.12em;
  text-transform: lowercase;
}

.nav-toggle {
  margin-left: auto;
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  min-height: 44px;
  min-width: 44px;
  padding: 0 0.7rem;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--paper);
  color: var(--ink);
  font: inherit;
  cursor: pointer;
}

.nav-toggle-bars {
  width: 1rem;
  height: 0.7rem;
  background:
    linear-gradient(var(--ink), var(--ink)) 0 0 / 100% 1.5px no-repeat,
    linear-gradient(var(--ink), var(--ink)) 0 50% / 100% 1.5px no-repeat,
    linear-gradient(var(--ink), var(--ink)) 0 100% / 100% 1.5px no-repeat;
}

.nav-toggle[aria-expanded="true"] .nav-toggle-bars {
  background:
    linear-gradient(var(--ink), var(--ink)) 0 50% / 100% 1.5px no-repeat;
}

.site-nav {
  margin-left: auto;
}

.nav-list {
  display: flex;
  gap: 0.25rem 1.25rem;
  list-style: none;
  margin: 0;
  padding: 0;
}

.nav-list a {
  display: inline-flex;
  align-items: center;
  min-height: 44px;
  color: var(--ink);
  text-decoration: none;
}

.nav-list a:hover,
.nav-list a[aria-current="page"] {
  color: var(--star);
}

@media (max-width: 767px) {
  .site-nav {
    position: fixed;
    z-index: var(--z-nav);
    top: var(--header-h);
    left: 0;
    right: 0;
    background: var(--paper);
    border-bottom: 1px solid var(--line);
    padding: 0.5rem 1rem 1rem;
    transform: translateY(-0.6rem);
    opacity: 0;
    visibility: hidden;
    pointer-events: none;
    transition: opacity 0.28s var(--ease), transform 0.28s var(--ease), visibility 0.28s;
  }

  .site-nav.is-open {
    transform: none;
    opacity: 1;
    visibility: visible;
    pointer-events: auto;
  }

  .nav-list {
    flex-direction: column;
  }

  .nav-list a {
    width: 100%;
  }
}

@media (min-width: 768px) {
  .nav-toggle {
    display: none;
  }

  .site-nav {
    position: static;
    opacity: 1;
    visibility: visible;
    pointer-events: auto;
    transform: none;
    background: transparent;
    border: 0;
    padding: 0;
  }
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 44px;
  padding: 0.55rem 1.05rem;
  border-radius: var(--radius);
  border: 1px solid transparent;
  font: inherit;
  letter-spacing: 0.02em;
  text-decoration: none;
  cursor: pointer;
  white-space: nowrap;
  transition: transform 0.18s var(--ease), background-color 0.18s var(--ease), color 0.18s var(--ease);
}

.btn:active {
  transform: translateY(1px);
}

.btn-primary {
  background: var(--star);
  color: var(--on-star);
  border-color: var(--star);
}

.btn-primary:hover {
  color: var(--on-star);
  background: color-mix(in srgb, var(--star) 86%, var(--ink));
}

.btn-ghost {
  background: transparent;
  color: var(--ink);
  border-color: var(--line);
}

.btn-ghost:hover {
  color: var(--star);
  border-color: var(--star);
}

.btn-quiet {
  background: var(--paper);
  color: var(--ink);
  border-color: var(--line);
}

.btn-quiet:hover {
  border-color: var(--star);
  color: var(--star);
}

.hero {
  position: relative;
  isolation: isolate;
  min-height: calc(100dvh - var(--header-h));
  padding: 2.25rem 0 3.5rem;
}

.hero-grid {
  position: relative;
  z-index: var(--z-content);
  display: grid;
  gap: 2.25rem;
}

.hero-copy {
  padding-top: 0.4rem;
}

.hero h1 {
  margin: 0;
  font-size: clamp(2rem, 7.2vw, 4rem);
  font-weight: 600;
  line-height: 1.18;
  letter-spacing: 0.04em;
  text-wrap: balance;
  word-break: keep-all;
}

.hero-lead {
  margin: 1.1rem 0 1.5rem;
  max-width: 22em;
  color: var(--ink-soft);
  font-size: 1.05rem;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.7rem;
}

.star-sketch {
  position: absolute;
  z-index: var(--z-star);
  width: 2.6rem;
  fill: none;
  stroke: var(--star);
  stroke-width: 0.7;
  opacity: 0.45;
  pointer-events: none;
}

.star-a {
  top: 12%;
  right: 8%;
}

.star-b {
  bottom: 14%;
  left: 6%;
  width: 1.5rem;
  opacity: 0.32;
}

.demo {
  margin: 0;
  display: grid;
  gap: 1rem;
}

.demo-label {
  margin: 0;
  color: var(--star);
  font-weight: 600;
  letter-spacing: 0.12em;
}

.demo-note,
.demo-status,
.demo-noscript {
  margin: 0.35rem 0 0;
  color: var(--ink-soft);
  font-size: 0.92rem;
}

.phone {
  justify-self: start;
  width: min(100%, 18.75rem);
}

.phone-shell {
  aspect-ratio: 9 / 18.4;
  padding: 0.72rem;
  border-radius: var(--radius-device);
  border: 1px solid var(--line);
  background:
    linear-gradient(180deg, color-mix(in srgb, var(--paper) 70%, var(--paper-2)), var(--paper-2));
  box-shadow: 0 22px 48px var(--shadow);
}

.phone-glass {
  height: 100%;
  display: flex;
  flex-direction: column;
  gap: 0.7rem;
  padding: 0.85rem 0.8rem 1rem;
  border-radius: calc(var(--radius-device) - 8px);
  background: var(--paper);
  border: 1px solid color-mix(in srgb, var(--line) 70%, var(--paper));
  overflow: hidden;
}

.phone-rail {
  width: 3.4rem;
  height: 0.28rem;
  margin: 0.15rem auto 0.35rem;
  border-radius: 99px;
  background: var(--line);
}

.phone-app {
  margin: 0;
  font-size: 0.82rem;
  letter-spacing: 0.18em;
  color: var(--ink-soft);
}

.transcript {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 0.7rem;
  flex: 1;
  min-height: 0;
  align-content: start;
  overflow-y: auto;
}

.bubble {
  display: grid;
  gap: 0.18rem;
  padding: 0.65rem 0.75rem;
  border-radius: var(--radius);
  max-width: 92%;
}

.bubble-who {
  font-size: 0.72rem;
  letter-spacing: 0.08em;
  color: var(--ink-soft);
}

.bubble-text {
  font-size: 0.92rem;
  line-height: 1.55;
}

.bubble-user {
  justify-self: end;
  background: var(--paper-2);
}

.bubble-bot,
.bubble-sys {
  justify-self: start;
  background: color-mix(in srgb, var(--star) 10%, var(--paper));
  border: 1px solid color-mix(in srgb, var(--star) 22%, var(--paper));
}

.bubble-sys {
  max-width: 100%;
}

.demo-board {
  display: grid;
  gap: 0.75rem;
}

.scene-set {
  margin: 0;
  padding: 0;
  border: 0;
}

.scene-set legend {
  padding: 0;
  margin-bottom: 0.4rem;
  font-size: 0.92rem;
}

.scene-options {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.scene-option {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  min-height: 44px;
  padding: 0 0.85rem;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  cursor: pointer;
}

.scene-option:has(input:checked) {
  border-color: var(--star);
  color: var(--star);
}

.scene-option input {
  width: 1.05rem;
  height: 1.05rem;
  accent-color: var(--star);
}

.demo-buttons {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.progress {
  padding: 4.5rem 0;
}

.progress-grid {
  display: grid;
  gap: 0.75rem;
  max-width: 42rem;
  margin-right: auto;
}

.section-lead {
  margin: 0 0 1.5rem;
  color: var(--ink-soft);
  max-width: 36em;
}

h2 {
  margin: 0;
  font-size: clamp(1.55rem, 3vw, 2.1rem);
  font-weight: 600;
  letter-spacing: 0.04em;
  line-height: 1.25;
}

h3 {
  margin: 0 0 0.35rem;
  font-size: 1.05rem;
  font-weight: 600;
}

.progress-list {
  list-style: none;
  margin: 0;
  padding: 0;
  border-left: 1px solid color-mix(in srgb, var(--star) 45%, var(--line));
}

.progress-list li {
  position: relative;
  padding: 0 0 1.6rem 1.4rem;
}

.progress-list li:last-child {
  padding-bottom: 0;
}

.progress-list li::before {
  content: "";
  position: absolute;
  left: -0.28rem;
  top: 0.45rem;
  width: 0.5rem;
  height: 0.5rem;
  background: var(--paper);
  border: 1px solid var(--star);
  transform: rotate(45deg);
}

.progress-list p {
  margin: 0;
  color: var(--ink-soft);
}

.versions {
  padding: 1rem 0 4.5rem;
}

.table-scroll {
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}

.compare {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.98rem;
}

.compare th,
.compare td {
  text-align: left;
  vertical-align: top;
  padding: 0.95rem 1rem 0.95rem 0;
  border-bottom: 1px solid var(--line);
  overflow-wrap: break-word;
}

.compare thead th {
  color: var(--star);
  font-weight: 600;
  letter-spacing: 0.06em;
}

.compare tbody th {
  width: 8.5rem;
  font-weight: 600;
  padding-right: 1.25rem;
}

.compare tr:last-child th,
.compare tr:last-child td {
  border-bottom: 0;
}

@media (max-width: 767px) {
  .compare thead {
    position: absolute;
    width: 1px;
    height: 1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
  }

  .compare,
  .compare tbody,
  .compare tr,
  .compare th,
  .compare td {
    display: block;
    width: 100%;
  }

  .compare tr {
    padding: 1rem 0 0.25rem;
    border-bottom: 1px solid var(--line);
  }

  .compare tr:last-child {
    border-bottom: 0;
  }

  .compare tbody th,
  .compare td {
    border: 0;
    padding: 0.2rem 0;
    width: auto;
  }

  .compare td::before {
    content: attr(data-label);
    display: block;
    margin-top: 0.55rem;
    color: var(--star);
    font-size: 0.82rem;
    letter-spacing: 0.06em;
  }
}

.faq {
  padding: 0 0 4.5rem;
}

.faq-wrap {
  max-width: 42rem;
  margin-right: auto;
}

.faq-list {
  margin-top: 1.25rem;
}

.faq-list details {
  border-top: 1px solid var(--line);
}

.faq-list details:last-child {
  border-bottom: 1px solid var(--line);
}

.faq-list summary {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  min-height: 44px;
  padding: 0.85rem 0;
  cursor: pointer;
  list-style: none;
  font-weight: 600;
}

.faq-list summary::-webkit-details-marker {
  display: none;
}

.faq-list summary::after {
  content: "";
  width: 0.55rem;
  height: 0.55rem;
  border-right: 1.5px solid var(--star);
  border-bottom: 1.5px solid var(--star);
  transform: rotate(45deg);
  flex: 0 0 auto;
}

.faq-list details[open] summary::after {
  transform: rotate(225deg);
}

.faq-list details p {
  margin: 0 0 1rem;
  color: var(--ink-soft);
}

.privacy-band {
  background: var(--paper-2);
  padding: 3.5rem 0;
}

.privacy-grid {
  max-width: 36rem;
}

.privacy-grid p:last-child {
  margin-bottom: 0;
}

.page-main {
  padding: 2.5rem 0 4rem;
  min-height: calc(100dvh - var(--header-h) - 12rem);
}

.legal {
  max-width: 40rem;
  margin-right: auto;
}

.legal-kicker {
  margin: 0 0 0.6rem;
  color: var(--star);
  letter-spacing: 0.1em;
}

.legal h1 {
  margin: 0 0 1rem;
  font-size: clamp(1.8rem, 4vw, 2.6rem);
  letter-spacing: 0.04em;
}

.legal-lead {
  color: var(--ink-soft);
}

.legal h2 {
  margin: 2rem 0 0.7rem;
  font-size: 1.15rem;
}

.legal ul {
  margin: 0;
  padding-left: 1.1rem;
}

.legal li + li {
  margin-top: 0.45rem;
}

.missing {
  padding-top: 2rem;
}

.missing .btn {
  margin-top: 0.5rem;
}

.site-footer {
  border-top: 1px solid var(--line);
  padding: 2.5rem 0 3rem;
  color: var(--ink-soft);
  font-size: 0.95rem;
}

.footer-grid {
  display: grid;
  gap: 1.75rem;
}

.footer-brand {
  margin: 0 0 0.4rem;
  color: var(--ink);
  font-weight: 600;
}

.footer-brand span {
  display: block;
  margin-top: 0.15rem;
  font-weight: 400;
  color: var(--ink-soft);
  letter-spacing: 0.06em;
}

.footer-h {
  margin: 0 0 0.4rem;
  font-size: 0.82rem;
  letter-spacing: 0.12em;
  color: var(--ink);
}

.site-footer p {
  margin: 0 0 0.35rem;
}

@media (min-width: 768px) {
  .hero {
    padding: 2.5rem 0 4.5rem;
  }

  .hero-grid {
    grid-template-columns: minmax(0, 1.2fr) minmax(0, 1fr);
    align-items: start;
    gap: 2rem 2.25rem;
  }

  .hero-copy {
    max-width: 28rem;
    padding-top: 1.1rem;
  }

  .demo {
    margin-top: 0.4rem;
    width: 100%;
    max-width: 22rem;
    margin-left: auto;
  }

  .phone {
    width: 100%;
    justify-self: stretch;
  }

  .progress {
    padding: 5.5rem 0 4.5rem;
  }

  .progress-grid,
  .faq-wrap,
  .privacy-grid,
  .legal {
    padding-left: 2vw;
  }

  .versions .wrap {
    padding-left: 2vw;
  }

  .compare tbody th {
    width: 9.5rem;
  }

  .footer-grid {
    grid-template-columns: minmax(0, 1fr) minmax(0, 1fr);
    gap: 2rem;
    align-items: start;
  }
}

@media (min-width: 1024px) {
  .hero-grid {
    gap: 3.5rem;
    padding-left: 2vw;
  }

  .footer-grid {
    grid-template-columns: minmax(0, 1.1fr) minmax(0, 1fr) minmax(0, 0.9fr);
    gap: 3rem;
  }
}

@media (min-width: 1440px) {
  .hero-grid {
    padding-left: 4vw;
    column-gap: 5rem;
  }

  .hero-copy {
    padding-top: 1.8rem;
  }

  .star-a {
    right: 14%;
  }
}

@media (prefers-reduced-motion: no-preference) {
  .bubble.is-enter {
    animation: bubble-in 0.42s var(--ease) both;
  }
}

@keyframes bubble-in {
  from {
    opacity: 0;
    transform: translateY(8px);
  }
  to {
    opacity: 1;
    transform: none;
  }
}

body.nav-open {
  overflow: hidden;
}

/* Maintainer visual pass: compact concept device, natural message height, readable hero. */
.site-header { background: var(--paper); backdrop-filter: none; }
.hero { padding-block: 2.5rem 4rem; min-height: auto; }
.hero-grid { align-items: center; }
.hero-copy { padding-block: 2rem; }
.hero h1 { font-weight: 650; letter-spacing: -.025em; }
.hero-lead { max-width: 27em; line-height: 1.85; }
.availability { margin: 1.5rem 0; font-size: .82rem; color: var(--ink-soft); }
.demo { width: min(100%, 21rem); justify-self: center; gap: .85rem; }
.demo .phone { width: min(100%, 17rem); margin-inline: auto; justify-self: center; }
.phone-shell { aspect-ratio: 9 / 14; }
.phone-mast { display: flex; align-items: center; gap: .65rem; padding-bottom: .6rem; }
.phone-mast img { border-radius: 12px; }
.phone-mast span { font-size: .65rem; color: var(--ink-soft); }
.phone-app { font-size: .9rem; font-weight: 600; color: var(--ink); }
.bubble { align-content: start; }
.bubble-text { font-size: .82rem; }
.concept-input { display: flex; gap: .5rem; align-items: center; justify-content: space-between; border-top: 1px solid var(--line); padding-top: .7rem; font-size: .68rem; color: var(--ink-soft); }
.concept-send { display: grid; place-items: center; width: 28px; height: 28px; border-radius: 50%; background: var(--star); color: var(--on-star); font-size: 1rem; }
.demo-board { gap: .5rem; }
.demo-status { font-size: .75rem; }
.scene-set legend { font-size: .75rem; margin-bottom: .2rem; }
.scene-options { gap: .35rem; }
.scene-option { font-size: .75rem; padding-inline: .5rem; }
.demo-buttons .btn { font-size: .75rem; padding: .4rem .75rem; }
.progress { background: var(--paper-2); padding-block: 5rem; }
.progress-grid { max-width: 72rem; gap: 1.75rem; }
.versions, .faq, .privacy-section { padding-block: 4rem; }
@media (min-width: 1000px) {
  .hero-grid { grid-template-columns: minmax(0, 1.2fr) minmax(0, .8fr); gap: 5rem; }
  .hero h1 { font-size: clamp(3.5rem, 5.1vw, 5rem); }
  .progress-grid { grid-template-columns: .8fr 1.2fr; column-gap: 6rem; }
  .progress-grid .section-lead { grid-column: 1; }
  .progress-list { grid-column: 2; grid-row: 1 / span 2; }
}
@media (max-width: 767px) {
  .hero { padding-top: 1.25rem; }
  .hero-copy { padding-top: .5rem; padding-bottom: 0; }
  .hero h1 { font-size: clamp(2.15rem, 9vw, 3.3rem); }
  .hero-lead { font-size: 1rem; }
  .hero-grid { gap: 2.75rem; }
  .demo { width: min(100%, 21rem); }
}

/* Progressive enhancement: navigation and the full page remain usable without JS. */
html:not(.js-enabled) .nav-toggle,
html:not(.js-enabled) .scene-set,
html:not(.js-enabled) .demo-buttons { display: none; }
@media (max-width: 767px) {
  html:not(.js-enabled) .site-header { height: auto; position: static; }
  html:not(.js-enabled) .header-inner { height: auto; min-height: var(--header-h); flex-wrap: wrap; }
  html:not(.js-enabled) .site-nav { position: static; opacity: 1; visibility: visible; pointer-events: auto; transform: none; width: 100%; padding: 0 0 1rem; border: 0; }
  html:not(.js-enabled) .nav-list { flex-direction: row; flex-wrap: wrap; gap: .25rem 1rem; }
}

/* Edition identity is communicated by name and a plus mark, not color alone. */
.edition-identities { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 1.5rem; margin: 1.75rem 0 2rem; }
.edition-identity { display: flex; align-items: center; gap: 1rem; min-width: 0; }
.edition-identity img { width: 64px; height: 64px; object-fit: contain; flex-shrink: 0; border-radius: 14px; }
.edition-identity strong { font-size: 1.1rem; }
.edition-identity p { margin: .25rem 0 0; font-size: .9rem; }
@media (max-width: 600px) { .edition-identities { grid-template-columns: 1fr; gap: 1.25rem; } }