:root{
  --warm-white:#fdf8f1;
  --warm-card:#ffffff;
  --warm-line:#ebe0d2;
  --cool-white:#f3f7fc;
  --cool-card:#ffffff;
  --cool-line:#dce5f0;
  --divider-dark:#2a2e35;
  --divider-hover:#1f2329;
  --accent:#1e56a0;
  --accent-warm:#b8652a;
  --ink:#1a222d;
  --mute:#5b6777;
  --max:1180px;
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0;
  color:var(--ink);
  background:var(--cool-white);
  font:16px/1.68 -apple-system,BlinkMacSystemFont,"Segoe UI","PingFang SC","Microsoft YaHei",sans-serif;
}
a{color:inherit;text-decoration:none}
img{max-width:100%;height:auto;display:block}
.wrap{width:min(var(--max),calc(100% - 40px));margin:0 auto}

/* Top Navigation */
.site-nav{
  position:sticky;top:0;z-index:80;
  background:rgba(42,46,53,.96);
  backdrop-filter:blur(10px);
  color:#fff;
  border-bottom:1px solid rgba(255,255,255,.12);
}
.nav-inner{
  height:68px;
  display:grid;
  grid-template-columns:auto 1fr auto;
  align-items:center;
  gap:22px;
}
.brand{
  display:inline-flex;align-items:center;gap:10px;
  font-weight:800;font-size:18px;color:#fff;
}
.brand-mark{
  width:34px;height:34px;border-radius:9px;
  display:grid;place-items:center;
  background:var(--accent);color:#fff;
  font-weight:900;font-size:14px;
}
.nav-links{
  display:flex;justify-content:center;gap:26px;
  font-size:14px;font-weight:600;color:rgba(255,255,255,.84);
}
.nav-links a:hover{color:#fff}

/* Buttons */
.btn{
  display:inline-flex;align-items:center;justify-content:center;gap:8px;
  min-height:42px;padding:0 20px;border-radius:10px;
  background:var(--accent);color:#fff;
  border:1px solid var(--accent);
  font-weight:700;font-size:14px;
  transition:transform .15s ease,opacity .15s ease;
  white-space:nowrap;
  cursor:pointer;
}
.btn:hover{transform:translateY(-1px);opacity:.93}
.btn-warm{background:var(--accent-warm);border-color:var(--accent-warm)}
.btn-ghost{
  background:var(--warm-card);color:var(--ink);
  border:1px solid var(--warm-line);
}
.btn-ghost:hover{border-color:var(--accent)}

/* Dual Independent Scroll Split Workbench:
   Upper Pane: Warm White (#fdf8f1), slow scroll brand story & Hero (HelloWorld & HelloWorld官网)
   Middle Draggable Splitter Bar: Dark Gray (#2a2e35), hosts HelloWorld下载 CTA & drag handle
   Lower Pane: Cool White (#f3f7fc), fast scroll features (HelloWorld跨境电商助手 & a strip for HelloWorld翻译) */
.dual-scroll-workbench{
  padding:20px 0 36px;
}
.workbench-frame{
  border:2px solid var(--divider-dark);
  border-radius:20px;
  overflow:hidden;
  box-shadow:0 22px 56px rgba(26,34,45,.12);
  background:var(--cool-white);
}

/* Upper Independent Scroll Zone (Warm White) */
.upper-scroll-pane{
  background:var(--warm-white);
  height:var(--upper-h, 460px);
  min-height:240px;
  max-height:680px;
  overflow-y:auto;
  padding:32px 36px;
  scroll-behavior:smooth;
  border-bottom:1px solid var(--warm-line);
}
.upper-scroll-pane::-webkit-scrollbar{width:8px}
.upper-scroll-pane::-webkit-scrollbar-thumb{background:#d7c6b2;border-radius:999px}

.pane-badge-row{
  display:flex;justify-content:space-between;align-items:center;
  flex-wrap:wrap;gap:10px;margin-bottom:16px;
}
.pane-badge{
  display:inline-flex;align-items:center;gap:8px;
  padding:5px 12px;border-radius:999px;
  background:#f4e8d9;color:#6e3b16;
  font-size:12px;font-weight:800;
}
.cool-badge{
  background:#dfeafa;color:var(--accent);
}
.story-hero-grid{
  display:grid;
  grid-template-columns:1.15fr .85fr;
  gap:28px;
  align-items:center;
}
.story-hero-grid h1{
  font-size:clamp(28px,3.5vw,42px);
  line-height:1.16;
  margin:8px 0 12px;
  letter-spacing:-.5px;
}
.hero-sub{
  font-size:15.5px;color:var(--mute);margin:0 0 14px;
}
.hero-tags{
  display:flex;flex-wrap:wrap;gap:8px;margin-bottom:16px;
}
.hero-tags span{
  padding:4px 11px;border-radius:8px;
  background:var(--warm-card);
  border:1px solid var(--warm-line);
  font-size:12.5px;font-weight:700;color:#5a3d28;
}
.brand-story-box{
  background:var(--warm-card);
  border:1px solid var(--warm-line);
  border-left:4px solid var(--accent-warm);
  border-radius:12px;
  padding:14px 16px;
  margin-bottom:18px;
  font-size:14px;
}
.hero-shot{
  background:var(--warm-card);
  border:1px solid var(--warm-line);
  border-radius:14px;
  padding:12px;
}
.hero-shot img{
  border-radius:10px;width:100%;aspect-ratio:16/10;object-fit:cover;
}
.hero-shot span{
  display:block;padding:8px 4px 2px;font-size:12px;color:var(--mute);
}

/* Middle Draggable Dark Gray Divider Bar (hosts HelloWorld下载) */
.divider-bar-dark{
  background:var(--divider-dark);
  color:#fff;
  padding:10px 24px;
  display:flex;
  justify-content:space-between;
  align-items:center;
  gap:16px;
  flex-wrap:wrap;
  cursor:ns-resize;
  user-select:none;
  border-top:1px solid rgba(255,255,255,.15);
  border-bottom:1px solid rgba(255,255,255,.15);
}
.divider-bar-dark:hover{background:var(--divider-hover)}
.drag-grip{
  display:inline-flex;align-items:center;gap:10px;
  font-size:12.5px;font-weight:700;color:#d6dde6;
}
.grip-lines{
  display:inline-flex;flex-direction:column;gap:3px;
}
.grip-lines i{
  width:22px;height:2px;background:#9aa6b8;display:block;border-radius:2px;
}
.divider-center-cta{
  display:flex;align-items:center;gap:12px;flex-wrap:wrap;
}
.divider-pill{
  padding:4px 10px;border-radius:6px;
  background:rgba(255,255,255,.1);
  font-size:12px;color:#e2e8f0;font-weight:700;
}

/* Lower Independent Scroll Zone (Cool White) */
.lower-scroll-pane{
  background:var(--cool-white);
  height:var(--lower-h, 520px);
  min-height:280px;
  max-height:760px;
  overflow-y:auto;
  padding:32px 36px;
  scroll-behavior:smooth;
}
.lower-scroll-pane::-webkit-scrollbar{width:8px}
.lower-scroll-pane::-webkit-scrollbar-thumb{background:#b8c7dc;border-radius:999px}

/* Dedicated Strip inside Lower Zone: "下区一条 HelloWorld翻译" */
.translation-strip-bar{
  background:var(--cool-card);
  border:1px solid var(--cool-line);
  border-left:5px solid var(--accent);
  border-radius:14px;
  padding:16px 20px;
  margin-bottom:24px;
  display:flex;
  justify-content:space-between;
  align-items:center;
  flex-wrap:wrap;
  gap:14px;
  box-shadow:0 8px 20px rgba(30,86,160,.05);
}
.translation-strip-bar strong{
  font-size:16px;color:var(--accent);display:block;margin-bottom:2px;
}
.translation-strip-bar span{
  font-size:13.5px;color:var(--mute);
}

/* Standard Sections below Workbench */
.section{padding:48px 0}
.section.warm-sec{background:var(--warm-white);border-top:1px solid var(--warm-line);border-bottom:1px solid var(--warm-line)}
.section.cool-sec{background:var(--cool-white)}
.sec-head{
  display:flex;justify-content:space-between;align-items:flex-end;
  flex-wrap:wrap;gap:16px;margin-bottom:26px;
}
.sec-head h2{
  font-size:clamp(23px,3vw,34px);
  margin:6px 0 0;line-height:1.2;
}
.sec-head p{margin:0;color:var(--mute);font-size:14.5px;max-width:520px}

/* 6 Cards Grid (3x2) */
.grid-6{
  display:grid;
  grid-template-columns:repeat(3,1fr);
  gap:18px;
}
.card{
  background:#fff;
  border:1px solid var(--cool-line);
  border-radius:16px;
  padding:22px;
  transition:border-color .15s ease,transform .15s ease;
}
.warm-sec .card{border-color:var(--warm-line)}
.card:hover{
  border-color:var(--accent);
  transform:translateY(-2px);
}
.card-num{
  display:inline-flex;align-items:center;justify-content:center;
  padding:3px 10px;border-radius:7px;
  background:var(--divider-dark);color:#fff;
  font-size:11.5px;font-weight:800;margin-bottom:10px;
}
.card h3{margin:0 0 8px;font-size:18px;color:var(--ink)}
.card p{margin:0;font-size:14px;color:var(--mute)}

/* Dual Image Showcase */
.media-pair{
  display:grid;
  grid-template-columns:1fr 1fr;
  gap:20px;
  margin-top:24px;
}
.media-card{
  background:#fff;
  border:1px solid var(--cool-line);
  border-radius:16px;
  padding:12px;
}
.media-card img{
  border-radius:10px;width:100%;aspect-ratio:16/10;object-fit:cover;
}
.media-card span{
  display:block;padding:8px 4px 2px;font-size:12.5px;color:var(--mute);
}

/* Reviewer */
.reviewer{
  display:flex;align-items:center;gap:10px;
  margin-top:14px;padding-top:12px;border-top:1px solid var(--warm-line);
}
.avatar{
  width:36px;height:36px;border-radius:50%;
  display:grid;place-items:center;
  background:var(--accent);color:#fff;font-weight:800;font-size:13px;
}
.reviewer b{display:block;font-size:14px}
.reviewer small{font-size:12px;color:var(--mute)}

/* FAQ */
.faq-list{display:grid;gap:10px}
.faq-item{
  background:#fff;
  border:1px solid var(--cool-line);
  border-radius:14px;
  padding:2px 20px;
}
.faq-item summary{
  padding:15px 0;font-weight:700;cursor:pointer;list-style:none;
  display:flex;justify-content:space-between;align-items:center;
}
.faq-item summary::after{
  content:"+";
  width:26px;height:26px;border-radius:8px;
  display:grid;place-items:center;
  background:var(--cool-white);color:var(--accent);font-weight:900;
}
.faq-item[open] summary::after{content:"−";background:var(--accent);color:#fff}
.faq-item p{margin:0 0 15px;font-size:14px;color:var(--mute)}

/* Footer */
.site-footer{
  background:var(--divider-dark);
  color:#d5dce6;
  padding:50px 0 28px;
}
.footer-grid{
  display:grid;
  grid-template-columns:1.4fr repeat(3,1fr);
  gap:28px;
  padding-bottom:28px;
  border-bottom:1px solid rgba(255,255,255,.12);
}
.footer-grid h4{margin:0 0 12px;color:#fff;font-size:15px}
.footer-grid a{display:block;margin:8px 0;font-size:14px;color:#aab5c4}
.footer-grid a:hover{color:#fff}
.footer-copy{
  padding-top:18px;
  display:flex;justify-content:space-between;flex-wrap:wrap;gap:12px;
  font-size:13px;color:#aab5c4;
}

@media (max-width:960px){
  .nav-links{display:none}
  .story-hero-grid,.media-pair,.footer-grid{grid-template-columns:1fr}
  .grid-6{grid-template-columns:repeat(2,1fr)}
}
@media (max-width:560px){
  .grid-6{grid-template-columns:1fr}
  .upper-scroll-pane,.lower-scroll-pane{padding:20px}
}

/* PERF-OPTIMIZED: 硬件加速与防卡顿渲染优化 */
.site-nav,.topbar,.header,.fixed-mid-ribbon{
  -webkit-backdrop-filter:blur(10px);
  transform:translateZ(0);
  will-change:transform;
}
#features,#scenes,#reviews,#faq,#packages,#install,#privacy,.site-footer{
  content-visibility:auto;
  contain-intrinsic-size:1px 620px;
}
@media (prefers-reduced-motion:reduce){
  html{scroll-behavior:auto}
  *,*::before,*::after{animation-duration:.01ms !important;transition-duration:.01ms !important}
}