/* ==========================================================================
   MPC-HC 中国官方网站 — 设计系统
   配色以 Logo 的黑 / 白为主基调，辅以品牌蓝作强调色，扁平、现代、专业、无 emoji
   ========================================================================== */

:root {
  /* 墨色阶（源自 Logo 的黑色与白色） */
  --ink-950: #050607;
  --ink-900: #0b0c0e;
  --ink-800: #16181b;
  --ink-700: #23262a;
  --ink-600: #33373c;
  --ink-500: #4a4f56;
  --ink-400: #636a73;
  --ink-300: #8b929b;
  --ink-200: #c2c7cd;
  --ink-100: #e4e7ea;
  --ink-50:  #f0f2f4;

  --paper:      #ffffff;
  --paper-2:    #f6f7f8;
  --paper-3:    #eef0f2;
  --line:       #e6e8eb;
  --line-strong:#d4d7db;

  --accent:     #2563eb;
  --accent-hover:#1d4ed8;
  --accent-soft:#eaf1fe;
  --accent-light:#93c5fd;

  --radius-sm: 8px;
  --radius:    12px;
  --radius-lg: 18px;

  --shadow-sm: 0 1px 2px rgba(11,12,14,.06), 0 1px 3px rgba(11,12,14,.05);
  --shadow-md: 0 6px 20px rgba(11,12,14,.08), 0 2px 6px rgba(11,12,14,.05);
  --shadow-lg: 0 18px 50px rgba(11,12,14,.18);

  --maxw: 1120px;
  --gutter: 24px;

  --font-sans: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI",
    "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Noto Sans SC",
    "Helvetica Neue", Arial, sans-serif;
  --font-mono: ui-monospace, "SFMono-Regular", "Cascadia Code", "JetBrains Mono",
    "Consolas", "Liberation Mono", monospace;
}

* { box-sizing: border-box; }

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: 84px;
}

body {
  margin: 0;
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.7;
  color: var(--ink-800);
  background: var(--paper);
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation-duration: .01ms !important; transition-duration: .01ms !important; }
}

img, svg { display: block; max-width: 100%; }
a { color: inherit; text-decoration: none; }
button { font-family: inherit; cursor: pointer; }
h1, h2, h3, h4, p, ul, ol, figure { margin: 0; }
ul, ol { padding: 0; list-style: none; }

/* 焦点可见性 */
:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

/* 无障碍：跳转链接 */
.skip-link {
  position: absolute;
  left: -9999px;
  top: 0;
  z-index: 2000;
  background: var(--ink-900);
  color: #fff;
  padding: 10px 16px;
  border-radius: 0 0 var(--radius-sm) 0;
  font-size: 14px;
}
.skip-link:focus { left: 0; }

.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;
}

/* ---------- 布局容器 ---------- */
.container {
  width: 100%;
  max-width: var(--maxw);
  margin-inline: auto;
  padding-inline: var(--gutter);
}

/* ---------- 顶部导航 ---------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255,255,255,.86);
  backdrop-filter: saturate(180%) blur(14px);
  -webkit-backdrop-filter: saturate(180%) blur(14px);
  border-bottom: 1px solid var(--line);
}
.nav {
  display: flex;
  align-items: center;
  gap: 28px;
  height: 66px;
}
.brand {
  display: flex;
  align-items: center;
  gap: 11px;
  font-weight: 700;
  letter-spacing: -.01em;
  color: var(--ink-900);
}
.brand img { width: 34px; height: 34px; border-radius: 8px; }
.brand .brand-name { font-size: 17px; }
.brand .brand-name small { display: block; font-weight: 500; font-size: 11px; color: var(--ink-400); letter-spacing: .02em; }

.nav-links {
  display: flex;
  align-items: center;
  gap: 4px;
  margin-left: auto;
}
.nav-links a {
  position: relative;
  padding: 8px 14px;
  font-size: 15px;
  font-weight: 500;
  color: var(--ink-600);
  border-radius: var(--radius-sm);
  transition: color .16s ease, background-color .16s ease;
}
.nav-links a:hover { color: var(--ink-900); background: var(--ink-50); }
.nav-links a[aria-current="page"] { color: var(--accent); font-weight: 600; }
.nav-links a[aria-current="page"]::after {
  content: ""; position: absolute; left: 14px; right: 14px; bottom: 3px;
  height: 2px; background: var(--accent); border-radius: 2px;
}

.nav-cta {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 9px 18px;
  font-size: 15px;
  font-weight: 600;
  color: #fff;
  background: var(--accent);
  border-radius: 999px;
  white-space: nowrap;
  transition: background-color .16s ease, transform .1s ease;
}
.nav-cta:hover { background: var(--accent-hover); }
.nav-cta:active { transform: translateY(1px); }
.nav-cta svg { width: 15px; height: 15px; }

.nav-toggle {
  display: none;
  margin-left: auto;
  width: 42px; height: 42px;
  border: 1px solid var(--line);
  background: #fff;
  border-radius: var(--radius-sm);
  align-items: center;
  justify-content: center;
}
.nav-toggle svg { width: 20px; height: 20px; }

/* ---------- 按钮 ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 9px;
  padding: 13px 26px;
  font-size: 16px;
  font-weight: 600;
  line-height: 1.2;
  border-radius: 999px;
  border: 1px solid transparent;
  transition: background-color .16s ease, border-color .16s ease, color .16s ease, transform .1s ease;
}
.btn:active { transform: translateY(1px); }
.btn svg { width: 18px; height: 18px; }

.btn-primary { background: var(--accent); color: #fff; }
.btn-primary:hover { background: var(--accent-hover); }

.btn-on-dark { background: var(--accent); color: #fff; }
.btn-on-dark:hover { background: var(--accent-hover); }

.btn-outline { background: transparent; color: var(--ink-800); border-color: var(--line-strong); }
.btn-outline:hover { border-color: var(--accent); color: var(--accent); background: var(--accent-soft); }

.btn-outline-on-dark { background: transparent; color: #fff; border-color: rgba(255,255,255,.35); }
.btn-outline-on-dark:hover { background: rgba(255,255,255,.1); border-color: #fff; color: #fff; }

.btn-lg { padding: 16px 34px; font-size: 17px; }
.btn-sm { padding: 9px 18px; font-size: 14px; }

/* ---------- 页头区（内页 hero） ---------- */
.page-hero {
  padding: 72px 0 64px;
  background: var(--ink-950);
  color: #fff;
  position: relative;
  overflow: hidden;
}
.page-hero::before {
  content: "";
  position: absolute; inset: 0;
  background:
    radial-gradient(600px 300px at 85% -10%, rgba(255,255,255,.10), transparent 60%),
    radial-gradient(500px 260px at -5% 110%, rgba(255,255,255,.06), transparent 55%);
}
.page-hero .container { position: relative; }
.eyebrow {
  display: inline-flex; align-items: center; gap: 8px;
  font-size: 13px; font-weight: 600; letter-spacing: .08em;
  text-transform: uppercase; color: var(--ink-300);
}
.eyebrow .dot { width: 7px; height: 7px; background: var(--accent-light); border-radius: 50%; opacity: .95; }
.page-hero h1 { font-size: clamp(30px, 5vw, 46px); line-height: 1.15; letter-spacing: -.02em; margin-top: 18px; font-weight: 800; }
.page-hero .lead { max-width: 640px; margin-top: 18px; font-size: 18px; color: var(--ink-200); }

.breadcrumb { margin-top: 26px; font-size: 13px; color: var(--ink-300); }
.breadcrumb a:hover { color: #fff; }
.breadcrumb .sep { margin: 0 8px; color: var(--ink-500); }

/* ---------- 区块通用 ---------- */
.section { padding: 88px 0; }
.section--alt { background: var(--paper-2); }
.section--dark { background: var(--ink-950); color: #fff; }

.section-head { max-width: 700px; margin-bottom: 48px; }
.section-head.center { margin-inline: auto; text-align: center; }
.section-head h2 { font-size: clamp(26px, 3.6vw, 38px); line-height: 1.2; letter-spacing: -.02em; font-weight: 800; color: var(--ink-900); }
.section-head p { margin-top: 14px; font-size: 17px; color: var(--ink-500); }
.section--dark .section-head h2 { color: #fff; }
.section--dark .section-head p { color: var(--ink-300); }
.kicker {
  display: inline-block; font-size: 13px; font-weight: 700; letter-spacing: .1em;
  text-transform: uppercase; color: var(--accent);
}
.section--dark .kicker { color: var(--accent-light); }

/* ---------- 卡片网格 ---------- */
.grid { display: grid; gap: 22px; }
.grid-3 { grid-template-columns: repeat(3, 1fr); }
.grid-4 { grid-template-columns: repeat(4, 1fr); }
.grid-2 { grid-template-columns: repeat(2, 1fr); }

.card {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius-lg);
  padding: 28px;
  transition: border-color .18s ease, box-shadow .18s ease, transform .18s ease;
}
.card:hover { border-color: var(--line-strong); box-shadow: var(--shadow-md); transform: translateY(-2px); }
.card .icon {
  width: 46px; height: 46px;
  display: grid; place-items: center;
  background: var(--accent); color: #fff;
  border-radius: 12px; margin-bottom: 18px;
}
.card .icon svg { width: 22px; height: 22px; }
.card h3 { font-size: 18px; font-weight: 700; letter-spacing: -.01em; color: var(--ink-900); }
.card p { margin-top: 10px; font-size: 15px; color: var(--ink-500); }

.card--numbered { counter-increment: num; position: relative; }
.card--numbered .num {
  font-family: var(--font-mono); font-size: 13px; font-weight: 600;
  color: var(--ink-400); letter-spacing: .05em;
  display: block; margin-bottom: 14px;
}

/* 深色卡片 */
.card--dark { background: rgba(255,255,255,.04); border-color: rgba(255,255,255,.12); }
.card--dark:hover { border-color: rgba(255,255,255,.24); }
.card--dark h3 { color: #fff; }
.card--dark p { color: var(--ink-200); }

/* ---------- 首页 Hero ---------- */
.hero {
  position: relative;
  background: var(--ink-950);
  color: #fff;
  overflow: hidden;
}
.hero::before {
  content: "";
  position: absolute; inset: 0;
  background:
    radial-gradient(760px 420px at 82% -6%, rgba(255,255,255,.12), transparent 58%),
    radial-gradient(600px 360px at -8% 100%, rgba(255,255,255,.07), transparent 55%);
}
.hero-inner {
  position: relative;
  display: grid;
  grid-template-columns: 1.15fr .85fr;
  gap: 48px;
  align-items: center;
  padding: 96px 0 104px;
}
.hero-badge {
  display: inline-flex; align-items: center; gap: 10px;
  padding: 7px 14px 7px 9px;
  border: 1px solid rgba(255,255,255,.18);
  border-radius: 999px;
  font-size: 13px; font-weight: 500; color: var(--ink-200);
  background: rgba(255,255,255,.04);
}
.hero-badge .pill {
  background: var(--accent); color: #fff;
  font-weight: 700; font-size: 12px; padding: 2px 9px; border-radius: 999px;
}
.hero h1 { font-size: clamp(34px, 5.4vw, 58px); line-height: 1.08; letter-spacing: -.025em; font-weight: 800; margin-top: 24px; }
.hero h1 .accent { color: var(--ink-300); font-weight: 500; }
.hero .lead { margin-top: 22px; max-width: 560px; font-size: 19px; color: var(--ink-200); }
.hero-actions { display: flex; flex-wrap: wrap; gap: 14px; margin-top: 34px; }
.hero-meta { display: flex; flex-wrap: wrap; gap: 22px; margin-top: 34px; font-size: 14px; color: var(--ink-300); }
.hero-meta span { display: inline-flex; align-items: center; gap: 8px; }
.hero-meta svg { width: 16px; height: 16px; opacity: .8; }

.hero-art {
  position: relative;
  display: grid; place-items: center;
}
.hero-art .frame {
  width: 100%; max-width: 430px;
  aspect-ratio: 16/10;
  background: linear-gradient(160deg, #1b1e22, #0d0f11);
  border: 1px solid rgba(255,255,255,.14);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
  display: grid; place-items: center;
  position: relative;
}
.hero-art .frame img { width: 96px; height: 96px; border-radius: 20px; }
.hero-art .frame .play {
  position: absolute; inset: 0; margin: auto;
  width: 64px; height: 64px; border-radius: 50%;
  background: var(--accent);
  box-shadow: 0 8px 24px rgba(37,99,235,.35);
  display: grid; place-items: center;
}
.hero-art .frame .play svg { width: 26px; height: 26px; color: #fff; margin-left: 4px; }
.hero-art .chip {
  position: absolute;
  background: #fff; color: var(--ink-900);
  border-radius: 12px; padding: 10px 16px;
  font-size: 13px; font-weight: 600;
  box-shadow: var(--shadow-md);
  white-space: nowrap;
}
.hero-art .chip b { display: block; font-size: 11px; font-weight: 600; color: var(--ink-400); letter-spacing: .03em; }
.hero-art .chip.c1 { top: 8%; left: -2%; }
.hero-art .chip.c2 { bottom: 6%; right: -4%; }

/* ---------- 特性列表（两栏带图标） ---------- */
.feature-row {
  display: grid; grid-template-columns: repeat(2, 1fr); gap: 18px;
}
.feature-row .item {
  display: flex; gap: 16px; align-items: flex-start;
  padding: 20px; border: 1px solid var(--line); border-radius: var(--radius);
  background: #fff;
  transition: border-color .16s ease, box-shadow .16s ease;
}
.feature-row .item:hover { border-color: var(--line-strong); box-shadow: var(--shadow-sm); }
.feature-row .item .ic {
  flex: 0 0 auto; width: 40px; height: 40px;
  display: grid; place-items: center;
  background: var(--accent-soft); color: var(--accent);
  border-radius: 10px;
}
.feature-row .item .ic svg { width: 20px; height: 20px; }
.feature-row .item h3 { font-size: 16px; font-weight: 700; color: var(--ink-900); }
.feature-row .item p { margin-top: 4px; font-size: 14px; color: var(--ink-500); }

/* ---------- 数字要点 ---------- */
.stat-strip {
  display: grid; grid-template-columns: repeat(4, 1fr);
  gap: 1px; background: var(--line); border: 1px solid var(--line);
  border-radius: var(--radius-lg); overflow: hidden;
}
.stat {
  background: #fff; padding: 30px 24px; text-align: center;
}
.stat b { display: block; font-size: 34px; font-weight: 800; letter-spacing: -.02em; color: var(--ink-900); font-family: var(--font-mono); }
.stat span { display: block; margin-top: 6px; font-size: 14px; color: var(--ink-500); }

/* ---------- 下载页 ---------- */
.download-card {
  display: grid; grid-template-columns: 1.2fr .8fr; gap: 0;
  border: 1px solid var(--line); border-radius: var(--radius-lg); overflow: hidden;
  background: #fff; box-shadow: var(--shadow-sm);
}
.download-card .main {
  padding: 38px 38px;
}
.download-card .main .version-line {
  display: flex; align-items: center; gap: 12px; flex-wrap: wrap;
}
.download-card .main .vnum { font-family: var(--font-mono); font-size: 15px; font-weight: 600; color: var(--ink-600); }
.tag {
  display: inline-flex; align-items: center; gap: 6px;
  font-size: 12px; font-weight: 600; padding: 3px 10px;
  border-radius: 999px; background: var(--accent); color: #fff;
}
.tag--light { background: var(--ink-50); color: var(--ink-700); }
.download-card .main h2 { font-size: 26px; font-weight: 800; letter-spacing: -.01em; margin-top: 12px; color: var(--ink-900); }
.download-card .main p { margin-top: 12px; color: var(--ink-500); font-size: 15px; }
.download-card .side {
  padding: 38px; background: var(--paper-2);
  border-left: 1px solid var(--line);
  display: flex; flex-direction: column; justify-content: center; gap: 16px;
}
.spec-list > div {
  display: flex; justify-content: space-between; gap: 16px;
  padding: 9px 0; border-bottom: 1px dashed var(--line-strong);
  font-size: 14px;
}
.spec-list > div:last-child { border-bottom: 0; }
.spec-list dt { color: var(--ink-400); }
.spec-list dd { color: var(--ink-800); font-weight: 600; text-align: right; margin: 0; }

.version-note {
  margin-top: 16px; padding: 14px 18px;
  background: var(--paper-2); border: 1px solid var(--line);
  border-radius: var(--radius); font-size: 13.5px; color: var(--ink-500);
}

/* ---------- FAQ 手风琴 ---------- */
.faq-list { max-width: 820px; margin-inline: auto; display: flex; flex-direction: column; gap: 12px; }
.faq-item { border: 1px solid var(--line); border-radius: var(--radius); background: #fff; overflow: hidden; }
.faq-q {
  width: 100%; display: flex; align-items: center; justify-content: space-between; gap: 16px;
  padding: 20px 24px; background: transparent; border: 0; text-align: left;
  font-size: 16px; font-weight: 600; color: var(--ink-900);
}
.faq-q:hover { background: var(--ink-50); }
.faq-q .chev { flex: 0 0 auto; width: 22px; height: 22px; color: var(--ink-400); transition: transform .2s ease; }
.faq-item[open] .faq-q .chev { transform: rotate(180deg); }
.faq-a { padding: 0 24px 22px; color: var(--ink-500); font-size: 15px; }
.faq-a p + p { margin-top: 10px; }
.faq-a ul { list-style: disc; padding-left: 20px; }
.faq-a li { margin-top: 6px; }
.faq-a code {
  font-family: var(--font-mono); font-size: 13.5px;
  background: var(--ink-50); border: 1px solid var(--line);
  padding: 1px 6px; border-radius: 6px; color: var(--ink-800);
}

/* ---------- 关于 / 时间线 ---------- */
.timeline { position: relative; max-width: 780px; margin-inline: auto; padding-left: 28px; }
.timeline::before {
  content: ""; position: absolute; left: 8px; top: 4px; bottom: 4px;
  width: 2px; background: var(--line-strong);
}
.timeline li { position: relative; padding: 0 0 30px 28px; }
.timeline li::before {
  content: ""; position: absolute; left: -24px; top: 6px;
  width: 12px; height: 12px; border-radius: 50%;
  background: var(--accent); box-shadow: 0 0 0 4px var(--paper);
}
.timeline .year { font-family: var(--font-mono); font-size: 13px; font-weight: 700; color: var(--ink-400); letter-spacing: .04em; }
.timeline h3 { font-size: 18px; font-weight: 700; color: var(--ink-900); margin-top: 4px; }
.timeline p { margin-top: 8px; font-size: 15px; color: var(--ink-500); }

/* ---------- CTA 横幅 ---------- */
.cta-banner {
  background: var(--ink-900); color: #fff;
  border-radius: var(--radius-lg);
  padding: 56px 48px;
  display: flex; align-items: center; justify-content: space-between; gap: 32px;
  position: relative; overflow: hidden;
}
.cta-banner::before {
  content: ""; position: absolute; inset: 0;
  background: radial-gradient(500px 260px at 90% 0%, rgba(255,255,255,.12), transparent 60%);
}
.cta-banner h2 { font-size: 28px; font-weight: 800; letter-spacing: -.01em; position: relative; }
.cta-banner p { margin-top: 10px; color: var(--ink-200); position: relative; }
.cta-banner .btn { position: relative; flex: 0 0 auto; }

/* ---------- 页脚 ---------- */
.site-footer { background: var(--ink-950); color: var(--ink-300); padding: 64px 0 0; }
.footer-grid {
  display: grid; grid-template-columns: 1.4fr 1fr 1fr 1fr; gap: 40px;
  padding-bottom: 44px;
}
.footer-grid .brand { color: #fff; }
.footer-grid .about p { margin-top: 14px; font-size: 14px; line-height: 1.7; color: var(--ink-400); max-width: 300px; }
.footer-col h4 { font-size: 13px; font-weight: 700; letter-spacing: .08em; text-transform: uppercase; color: var(--ink-400); margin-bottom: 16px; }
.footer-col li { margin-bottom: 11px; }
.footer-col a { font-size: 14px; color: var(--ink-300); transition: color .15s ease; }
.footer-col a:hover { color: #fff; }
.footer-bottom {
  border-top: 1px solid rgba(255,255,255,.1);
  padding: 22px 0;
  display: flex; flex-wrap: wrap; gap: 14px; align-items: center; justify-content: space-between;
  font-size: 13px; color: var(--ink-400);
}
.footer-bottom .links { display: flex; gap: 20px; }
.footer-bottom a:hover { color: #fff; }

/* ---------- 下载弹窗 ---------- */
.modal-overlay {
  position: fixed; inset: 0; z-index: 1000;
  background: rgba(11,12,14,.62);
  backdrop-filter: blur(4px);
  -webkit-backdrop-filter: blur(4px);
  display: flex; align-items: center; justify-content: center;
  padding: 20px;
  opacity: 0; visibility: hidden;
  transition: opacity .22s ease, visibility .22s ease;
}
.modal-overlay.is-open { opacity: 1; visibility: visible; }
.modal {
  width: 100%; max-width: 560px;
  background: #fff; border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
  overflow: hidden;
  transform: translateY(14px) scale(.98);
  transition: transform .22s ease;
}
.modal-overlay.is-open .modal { transform: none; }
.modal-head {
  display: flex; align-items: flex-start; justify-content: space-between; gap: 16px;
  padding: 24px 26px 0;
}
.modal-head h3 { font-size: 21px; font-weight: 800; letter-spacing: -.01em; color: var(--ink-900); }
.modal-head p { margin-top: 6px; font-size: 14px; color: var(--ink-500); }
.modal-close {
  flex: 0 0 auto; width: 36px; height: 36px;
  border: 1px solid var(--line); background: #fff; border-radius: 10px;
  display: grid; place-items: center; color: var(--ink-500);
  transition: background-color .15s ease, color .15s ease;
}
.modal-close:hover { background: var(--ink-50); color: var(--ink-900); }
.modal-close svg { width: 18px; height: 18px; }
.modal-body { padding: 22px 26px 28px; }

.qr-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
.qr-card {
  border: 1px solid var(--line); border-radius: var(--radius);
  padding: 18px; text-align: center; background: #fff;
}
.qr-card .qr-box {
  width: 100%; aspect-ratio: 1/1; max-width: 176px; margin: 0 auto;
  border: 1px solid var(--line); border-radius: 12px;
  padding: 10px; background: #fff;
}
.qr-card .qr-box img { width: 100%; height: 100%; }
.qr-card .name { margin-top: 14px; font-size: 15px; font-weight: 700; color: var(--ink-900); }
.qr-card .hint { margin-top: 4px; font-size: 13px; color: var(--ink-400); }
.qr-card a.link {
  display: inline-block; margin-top: 10px; font-size: 13px; color: var(--ink-600);
  border-bottom: 1px solid var(--line-strong); padding-bottom: 1px;
}
.qr-card a.link:hover { color: var(--accent); border-color: var(--accent); }
.modal-note {
  margin-top: 20px; padding: 13px 16px;
  background: var(--paper-2); border: 1px solid var(--line);
  border-radius: var(--radius); font-size: 13px; color: var(--ink-500);
  display: flex; gap: 10px; align-items: flex-start;
}
.modal-note svg { width: 17px; height: 17px; flex: 0 0 auto; margin-top: 2px; color: var(--ink-400); }

/* ---------- 返回顶部 ---------- */
.to-top {
  position: fixed; right: 24px; bottom: 24px; z-index: 90;
  width: 46px; height: 46px; border-radius: 50%;
  background: var(--accent); color: #fff; border: 0;
  display: grid; place-items: center; box-shadow: var(--shadow-md);
  opacity: 0; visibility: hidden; transform: translateY(8px);
  transition: opacity .2s ease, transform .2s ease, visibility .2s;
}
.to-top.show { opacity: 1; visibility: visible; transform: none; }
.to-top svg { width: 20px; height: 20px; }

/* ---------- 响应式 ---------- */
@media (max-width: 960px) {
  .grid-4 { grid-template-columns: repeat(2, 1fr); }
  .grid-3 { grid-template-columns: repeat(2, 1fr); }
  .stat-strip { grid-template-columns: repeat(2, 1fr); }
  .hero-inner { grid-template-columns: 1fr; padding: 72px 0 80px; }
  .hero-art { order: -1; }
  .hero-art .frame { max-width: 460px; }
  .download-card { grid-template-columns: 1fr; }
  .download-card .side { border-left: 0; border-top: 1px solid var(--line); }
  .feature-row { grid-template-columns: 1fr; }
  .footer-grid { grid-template-columns: 1fr 1fr; }
}

@media (max-width: 680px) {
  .nav-links {
    position: fixed; top: 66px; left: 0; right: 0;
    flex-direction: column; align-items: stretch; gap: 2px;
    background: #fff; border-bottom: 1px solid var(--line);
    padding: 12px 16px 18px;
    display: none;
  }
  .nav-links.is-open { display: flex; }
  .nav-links a { padding: 13px 14px; font-size: 16px; }
  .nav-toggle { display: inline-flex; }
  .nav-cta { display: none; }
  .grid-3, .grid-4, .grid-2 { grid-template-columns: 1fr; }
  .stat-strip { grid-template-columns: 1fr 1fr; }
  .qr-grid { grid-template-columns: 1fr; }
  .cta-banner { flex-direction: column; align-items: flex-start; padding: 40px 28px; }
  .section { padding: 64px 0; }
  .page-hero { padding: 56px 0 48px; }
  .hero-art .chip.c1 { left: 0; }
  .hero-art .chip.c2 { right: 0; }
}