/* 91PO官方网站 · 91-os.xyz · 原创视觉体系 */
:root {
  --bg-deep: #070708;
  --bg-panel: #111114;
  --bg-elevated: #18181d;
  --orange: #ff7a18;
  --orange-bright: #ff9a3c;
  --amber: #ffb347;
  --gold: #d4a853;
  --text: #f4f4f6;
  --text-muted: #9a9aa8;
  --line: rgba(255, 122, 24, 0.18);
  --radius: 16px;
  --radius-lg: 24px;
  --shadow: 0 24px 60px rgba(0, 0, 0, 0.45);
  --header-h: 62px;
  --sticky-bar-h: 0px;
  --site-top-offset: 62px;
  --font: "PingFang SC", "Microsoft YaHei", "Helvetica Neue", sans-serif;
}

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}
body {
  font-family: var(--font);
  background: var(--bg-deep);
  color: var(--text);
  line-height: 1.75;
  font-size: 15px;
  overflow: visible;
}
img { max-width: 100%; height: auto; display: block; }
a { color: var(--orange-bright); text-decoration: none; transition: color 0.2s; }
a:hover { color: var(--amber); }
.wrap { width: min(1120px, 92vw); margin: 0 auto; }

/* 单一固定顶栏容器（解决移动端 fixed 失效） */
.site-fixed-top {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  width: 100%;
  z-index: 1000;
  background: var(--bg-deep);
  border-bottom: 1px solid var(--line);
}
.page-root {
  padding-top: var(--site-top-offset);
  overflow-x: clip;
  min-height: 100vh;
}
@supports not (overflow: clip) {
  .page-root { overflow-x: hidden; }
}

/* Header */
.site-header {
  position: relative;
  z-index: 1;
  background: transparent;
  border-bottom: none;
}
.header-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  min-height: var(--header-h);
  gap: 16px;
}
.brand {
  display: flex;
  align-items: center;
  gap: 12px;
  color: var(--text);
}
.brand img { width: 42px; height: 42px; border-radius: 10px; }
.brand strong { display: block; font-size: 15px; letter-spacing: 0.02em; }
.brand em { display: block; font-style: normal; font-size: 11px; color: var(--text-muted); letter-spacing: 0.12em; text-transform: uppercase; }
.main-nav { display: flex; gap: 6px; }
.main-nav a {
  color: var(--text-muted);
  font-size: 14px;
  padding: 8px 14px;
  border-radius: 999px;
}
.main-nav a:hover, .main-nav a.active { color: var(--text); background: rgba(255, 122, 24, 0.12); }
.menu-btn {
  display: none;
  flex-direction: column;
  gap: 5px;
  background: none;
  border: none;
  cursor: pointer;
  padding: 8px;
}
.menu-btn span {
  display: block;
  width: 22px;
  height: 2px;
  background: var(--text);
  border-radius: 2px;
}
.mobile-drawer {
  display: none;
  position: fixed;
  top: var(--site-top-offset);
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(7, 7, 8, 0.97);
  z-index: 990;
  padding: 24px;
  flex-direction: column;
  gap: 8px;
}
.mobile-drawer.open { display: flex; }
.mobile-drawer a {
  color: var(--text);
  padding: 14px 16px;
  border-radius: var(--radius);
  background: var(--bg-panel);
  font-size: 16px;
}

/* Sticky download bar */
.sticky-apps {
  position: relative;
  z-index: 1;
  background: rgba(17, 17, 20, 0.98);
  border-top: 1px solid transparent;
  padding: 0;
  max-height: 0;
  overflow: hidden;
  opacity: 1;
  visibility: visible;
  pointer-events: none;
  transition: max-height 0.28s ease, padding 0.28s ease, border-color 0.28s ease;
}
.sticky-apps.show {
  max-height: 160px;
  padding: 10px 0;
  border-top-color: var(--line);
  pointer-events: auto;
}
@media (min-width: 769px) {
  .sticky-apps:not(.show) {
    height: 0;
    max-height: 0;
    padding: 0;
    border-top-color: transparent;
  }
}
.sticky-apps .ad-grid {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  align-items: flex-start;
  gap: 8px 6px;
}
.sticky-apps .ad-grid > div { width: calc(12.5% - 6px); min-width: 70px; max-width: 80px; }
@media (max-width: 768px) {
  .sticky-apps .ad-grid > div { width: calc(25% - 6px); }
}

/* Ads zone */
#ads, .ad-grid {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  align-items: flex-start;
  gap: 10px 8px;
}
#ads > div, .ad-grid > div {
  display: flex;
  flex-direction: column;
  align-items: center;
  width: 70px;
}
#ads img, .ad-grid img {
  width: 65px;
  height: 65px;
  object-fit: cover;
  border-radius: 18px;
  box-shadow: 0 6px 18px rgba(0, 0, 0, 0.35);
  transition: transform 0.18s ease, box-shadow 0.18s ease;
  border: 1px solid rgba(255, 122, 24, 0.2);
}
#ads a, .ad-grid a { display: inline-block; border-radius: 15px; text-decoration: none; }
#ads img:hover, .ad-grid img:hover {
  transform: translateY(-4px) scale(1.04);
  box-shadow: 0 10px 24px rgba(255, 122, 24, 0.25);
}
#ads .caption, .ad-grid .caption {
  height: 15px;
  font-size: 11px;
  color: var(--text-muted);
  text-align: center;
  max-width: 100px;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  margin-top: 4px;
}

.dl-banner {
  background: linear-gradient(135deg, rgba(255, 122, 24, 0.08), rgba(17, 17, 20, 0.95));
  border-bottom: 1px solid var(--line);
  padding: 18px 0 14px;
  scroll-margin-top: 8px;
}
.dl-banner-head { text-align: center; margin-bottom: 12px; }
.dl-banner-head h2 { font-size: clamp(17px, 4vw, 22px); font-weight: 600; margin-bottom: 6px; }
.dl-banner-head p { color: var(--text-muted); font-size: 13px; }

/* Hero */
.hero-block {
  position: relative;
  padding: 48px 0 56px;
  overflow: visible;
}
.hero-block::before {
  content: "";
  position: absolute;
  width: 520px;
  height: 520px;
  top: -180px;
  right: -120px;
  background: radial-gradient(circle, rgba(255, 122, 24, 0.22), transparent 68%);
  pointer-events: none;
}
.hero-block::after {
  content: "";
  position: absolute;
  width: 360px;
  height: 360px;
  bottom: -100px;
  left: -80px;
  background: radial-gradient(circle, rgba(212, 168, 83, 0.12), transparent 70%);
  pointer-events: none;
}
.hero-layout {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 40px;
  align-items: center;
  position: relative;
  z-index: 1;
}
.hero-copy { min-width: 0; }
.hero-visual {
  position: relative;
  width: 100%;
  max-width: 400px;
  min-height: 480px;
  height: 480px;
  margin: 0 auto;
  flex-shrink: 0;
  justify-self: center;
}
.hero-tag {
  display: inline-block;
  font-size: 12px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--orange-bright);
  border: 1px solid var(--line);
  padding: 6px 14px;
  border-radius: 999px;
  margin-bottom: 18px;
}
.hero-block h1 {
  font-size: clamp(28px, 5vw, 42px);
  line-height: 1.25;
  font-weight: 700;
  margin-bottom: 18px;
}
.hero-block h1 span { color: var(--orange-bright); }
.hero-intro {
  color: var(--text-muted);
  font-size: 16px;
  margin-bottom: 22px;
  max-width: 520px;
}
.hero-pills { display: flex; flex-wrap: wrap; gap: 8px; margin-bottom: 28px; }
.hero-pills span {
  font-size: 12px;
  padding: 6px 12px;
  border-radius: 999px;
  background: var(--bg-elevated);
  border: 1px solid rgba(255, 255, 255, 0.06);
  color: var(--text-muted);
}
.btn-primary {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 14px 32px;
  border-radius: 999px;
  background: linear-gradient(135deg, var(--orange), var(--amber));
  color: #111;
  font-weight: 600;
  font-size: 15px;
  border: none;
  cursor: pointer;
  box-shadow: 0 8px 28px rgba(255, 122, 24, 0.35);
  transition: transform 0.2s, box-shadow 0.2s;
}
.btn-primary:hover { transform: translateY(-2px); box-shadow: 0 12px 32px rgba(255, 122, 24, 0.45); color: #111; }
.btn-outline {
  display: inline-flex;
  padding: 13px 28px;
  border-radius: 999px;
  border: 1px solid var(--line);
  color: var(--text);
  font-size: 14px;
  margin-left: 12px;
}
.btn-outline:hover { border-color: var(--orange); color: var(--orange-bright); }

.hero-visual img {
  position: absolute;
  display: block;
  max-width: none;
  width: 52%;
  height: auto;
  object-fit: cover;
  border-radius: 20px;
  border: 2px solid rgba(255, 255, 255, 0.12);
  box-shadow: 0 20px 50px rgba(0, 0, 0, 0.55);
  background: var(--bg-elevated);
}
.hero-visual .hv-1 { top: 0; left: 2%; z-index: 4; transform: rotate(-8deg); width: 54%; }
.hero-visual .hv-2 { top: 6%; right: 0; z-index: 3; transform: rotate(5deg); width: 50%; }
.hero-visual .hv-3 { bottom: 12%; left: 6%; z-index: 2; transform: rotate(-3deg); width: 48%; }
.hero-visual .hv-4 { bottom: 0; right: 4%; z-index: 1; transform: rotate(8deg); width: 46%; }

/* 纯文案 SEO 模块 */
.seo-block {
  padding: 32px 28px;
  background: var(--bg-panel);
  border-radius: var(--radius-lg);
  border: 1px solid rgba(255, 255, 255, 0.04);
  margin-bottom: 32px;
}
.seo-block h3 {
  font-size: 20px;
  margin-bottom: 16px;
  color: var(--text);
}
.seo-block p { color: var(--text-muted); margin-bottom: 14px; font-size: 15px; }
.seo-block ul { padding-left: 20px; color: var(--text-muted); margin-bottom: 12px; }
.seo-block li { margin-bottom: 8px; font-size: 14px; }

.channel-table {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 14px;
  margin-top: 24px;
}
.channel-cell {
  padding: 20px 16px;
  background: var(--bg-elevated);
  border-radius: var(--radius);
  border: 1px solid rgba(255, 255, 255, 0.05);
}
.channel-cell h4 { font-size: 15px; margin-bottom: 8px; color: var(--orange-bright); }
.channel-cell p { font-size: 13px; color: var(--text-muted); line-height: 1.65; margin: 0; }

.preview-strip {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
  margin: 28px 0;
}
.preview-strip figure { margin: 0; }
.preview-strip img {
  border-radius: 12px;
  border: 1px solid rgba(255, 122, 24, 0.15);
  aspect-ratio: 9/16;
  object-fit: cover;
  width: 100%;
}
.preview-strip figcaption {
  font-size: 11px;
  color: var(--text-muted);
  text-align: center;
  margin-top: 6px;
  line-height: 1.4;
}

/* Metrics */
.metrics-row {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
  padding: 28px 0 40px;
  border-bottom: 1px solid rgba(255, 255, 255, 0.05);
}
.metric-cell {
  text-align: center;
  padding: 20px 12px;
  background: var(--bg-panel);
  border-radius: var(--radius);
  border: 1px solid rgba(255, 255, 255, 0.04);
}
.metric-cell strong {
  display: block;
  font-size: clamp(20px, 4vw, 28px);
  color: var(--orange-bright);
  margin-bottom: 4px;
}
.metric-cell span { font-size: 12px; color: var(--text-muted); }

/* Sections */
.section { padding: 56px 0; }
.section-kicker {
  font-size: 11px;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--orange);
  margin-bottom: 10px;
}
.section-title {
  font-size: clamp(22px, 4.5vw, 32px);
  font-weight: 700;
  margin-bottom: 14px;
  line-height: 1.3;
}
.section-lead {
  color: var(--text-muted);
  max-width: 720px;
  margin-bottom: 36px;
}

/* 3:7 content ratio */
.ratio-block {
  display: grid;
  grid-template-columns: 3fr 7fr;
  gap: 32px;
  align-items: start;
  margin-bottom: 48px;
  padding: 28px;
  background: var(--bg-panel);
  border-radius: var(--radius-lg);
  border: 1px solid rgba(255, 255, 255, 0.04);
}
.ratio-block.reverse { direction: rtl; }
.ratio-block.reverse > * { direction: ltr; }
.ratio-media img {
  border-radius: var(--radius);
  border: 1px solid rgba(255, 122, 24, 0.15);
  box-shadow: var(--shadow);
}
.ratio-body h3 {
  font-size: 20px;
  margin-bottom: 14px;
  color: var(--text);
}
.ratio-body p { color: var(--text-muted); margin-bottom: 14px; }
.ratio-body ul { padding-left: 18px; color: var(--text-muted); }
.ratio-body li { margin-bottom: 8px; }

/* Feature grid */
.feat-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 16px;
  margin-top: 32px;
}
.feat-card {
  padding: 24px 20px;
  background: var(--bg-elevated);
  border-radius: var(--radius);
  border: 1px solid rgba(255, 255, 255, 0.05);
  transition: border-color 0.2s, transform 0.2s;
}
.feat-card:hover { border-color: var(--line); transform: translateY(-3px); }
.feat-icon {
  width: 44px;
  height: 44px;
  border-radius: 12px;
  background: linear-gradient(135deg, rgba(255, 122, 24, 0.2), rgba(212, 168, 83, 0.15));
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 20px;
  margin-bottom: 14px;
}
.feat-card h4 { font-size: 16px; margin-bottom: 8px; }
.feat-card p { font-size: 13px; color: var(--text-muted); line-height: 1.65; }

/* Steps */
.steps-list { counter-reset: step; }
.step-item {
  display: grid;
  grid-template-columns: 56px 1fr;
  gap: 20px;
  padding: 24px 0;
  border-bottom: 1px solid rgba(255, 255, 255, 0.05);
}
.step-item::before {
  counter-increment: step;
  content: counter(step, decimal-leading-zero);
  font-size: 28px;
  font-weight: 700;
  color: var(--orange);
  opacity: 0.7;
}
.step-item h4 { font-size: 17px; margin-bottom: 8px; }
.step-item p { color: var(--text-muted); font-size: 14px; }

/* FAQ */
.faq-list { margin-top: 24px; }
.faq-item {
  border: 1px solid rgba(255, 255, 255, 0.06);
  border-radius: var(--radius);
  margin-bottom: 10px;
  overflow: hidden;
  background: var(--bg-panel);
}
.faq-q {
  width: 100%;
  text-align: left;
  background: none;
  border: none;
  color: var(--text);
  padding: 18px 20px;
  font-size: 15px;
  font-weight: 500;
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  align-items: center;
}
.faq-q::after { content: "+"; color: var(--orange); font-size: 20px; }
.faq-item.open .faq-q::after { content: "−"; }
.faq-a {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.3s ease;
}
.faq-a-inner {
  padding: 0 20px 18px;
  color: var(--text-muted);
  font-size: 14px;
}
.faq-item.open .faq-a { max-height: 400px; }

/* CTA band */
.cta-band {
  margin: 48px 0 0;
  padding: 40px 28px;
  text-align: center;
  border-radius: var(--radius-lg);
  background: linear-gradient(160deg, rgba(255, 122, 24, 0.15), var(--bg-elevated));
  border: 1px solid var(--line);
}
.cta-band h2 { font-size: clamp(20px, 4vw, 28px); margin-bottom: 12px; }
.cta-band p { color: var(--text-muted); margin-bottom: 22px; max-width: 560px; margin-left: auto; margin-right: auto; }

/* Subpages */
.page-hero {
  padding: 40px 0 28px;
  border-bottom: 1px solid rgba(255, 255, 255, 0.05);
}
.page-hero h1 { font-size: clamp(24px, 5vw, 34px); margin-bottom: 10px; }
.page-hero p { color: var(--text-muted); }
.breadcrumb {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  font-size: 13px;
  color: var(--text-muted);
  margin-bottom: 18px;
}
.breadcrumb a { color: var(--text-muted); }
.breadcrumb a:hover { color: var(--orange-bright); }
.breadcrumb span { color: var(--text-muted); opacity: 0.5; }
.prose { padding: 36px 0 56px; }
.prose h2 { font-size: 20px; margin: 32px 0 14px; color: var(--text); }
.prose h3 { font-size: 17px; margin: 24px 0 10px; }
.prose p, .prose li { color: var(--text-muted); margin-bottom: 12px; font-size: 14px; }
.prose ul, .prose ol { padding-left: 22px; margin-bottom: 16px; }

/* Footer */
.site-footer {
  border-top: 1px solid rgba(255, 255, 255, 0.06);
  padding: 36px 0 28px;
  background: var(--bg-panel);
}
.footer-grid {
  display: grid;
  grid-template-columns: 1.4fr 1fr 1fr;
  gap: 28px;
  margin-bottom: 28px;
}
.footer-brand img { width: 48px; border-radius: 12px; margin-bottom: 12px; }
.footer-brand p { font-size: 13px; color: var(--text-muted); max-width: 280px; }
.footer-col h5 { font-size: 13px; letter-spacing: 0.08em; margin-bottom: 14px; color: var(--text); }
.footer-col a {
  display: block;
  color: var(--text-muted);
  font-size: 13px;
  margin-bottom: 8px;
}
.footer-col a:hover { color: var(--orange-bright); }
.footer-bottom {
  padding-top: 20px;
  border-top: 1px solid rgba(255, 255, 255, 0.05);
  font-size: 12px;
  color: var(--text-muted);
  text-align: center;
}

/* Error pages */
.error-page {
  min-height: 60vh;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: 40px 0;
}
.error-page h1 { font-size: 72px; color: var(--orange); margin-bottom: 12px; }
.error-page p { color: var(--text-muted); margin-bottom: 24px; }

/* Responsive */
@media (max-width: 960px) {
  .hero-layout { grid-template-columns: 1fr; gap: 32px; }
  .hero-visual { order: -1; min-height: 400px; height: 400px; max-width: 320px; }
  .metrics-row { grid-template-columns: repeat(2, 1fr); }
  .feat-grid { grid-template-columns: repeat(2, 1fr); }
  .footer-grid { grid-template-columns: 1fr; }
  .ratio-block { grid-template-columns: 1fr; }
  .ratio-block.reverse { direction: ltr; }
  .channel-table { grid-template-columns: repeat(2, 1fr); }
  .preview-strip { grid-template-columns: repeat(2, 1fr); }
}
@media (max-width: 768px) {
  :root { --header-h: 56px; }
  .main-nav { display: none; }
  .menu-btn { display: flex; }
  .feat-grid { grid-template-columns: 1fr; }
  .btn-outline { margin-left: 0; margin-top: 12px; display: inline-flex; }
  .hero-block { padding: 32px 0 40px; }
  .hero-visual { min-height: 360px; height: 360px; max-width: 280px; }
  .section { padding: 40px 0; }
  .channel-table { grid-template-columns: 1fr; }
  /* 移动端顶栏已固定展示下载区，隐藏正文内重复的 dl-banner */
  .dl-banner { display: none; }
  .sticky-apps,
  .sticky-apps.show {
    max-height: 160px;
    padding: 8px 0;
    border-top-color: var(--line);
    pointer-events: auto;
  }
  .sticky-apps .ad-grid > div { width: calc(20% - 6px); min-width: 58px; max-width: 68px; }
  #ads > div, .ad-grid > div { width: 62px; }
  #ads img, .ad-grid img { width: 58px; height: 58px; }
}