/* Tokens, type, frame. One dark world: black ground, graphite surfaces, one celadon accent, a rose for "original".
   Headlines are a grotesque set tight (Noto Sans SC / Inter), as a product page reads; the serif stays in the
   wordmark only. */
:root {
  --bg: #000;
  --surface: #0E100F;
  --surface-2: #161918;
  --surface-3: #1D2120;
  --line: rgba(236, 233, 226, .08);
  --line-2: rgba(236, 233, 226, .16);
  --text: #F2F0EA;
  --mute: #9AA19C;
  --faint: #89938C;
  --accent: #9CCBB7;
  --accent-soft: rgba(156, 203, 183, .12);
  --rose: #E59A8C;
  --seal: #B4473A;
  --display: "Inter", "Noto Sans SC", "PingFang SC", "Microsoft YaHei", sans-serif;
  --body: "Inter", "Noto Sans SC", "PingFang SC", "Microsoft YaHei", sans-serif;
  --mono: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  --ease: cubic-bezier(.22, .8, .2, 1);
  --radius: 28px;
  color-scheme: dark;
}
* { box-sizing: border-box; }
[hidden] { display: none !important; }
html { scroll-behavior: smooth; }
body { margin: 0; background: var(--bg); color: var(--text); font: 400 17px/1.6 var(--body); -webkit-font-smoothing: antialiased; text-rendering: optimizeLegibility; }
body::before { content: ""; position: fixed; inset: 0 0 auto; height: env(safe-area-inset-top, 0px); z-index: 10; background: var(--bg); }
.wrap { max-width: 1120px; margin: 0 auto; padding-left: max(20px, env(safe-area-inset-left, 0px)); padding-right: max(20px, env(safe-area-inset-right, 0px)); }
@media (min-width: 900px) { .wrap { padding-left: max(40px, env(safe-area-inset-left, 0px)); padding-right: max(40px, env(safe-area-inset-right, 0px)); } }
h1, h2, h3 { font-family: var(--display); font-weight: 700; margin: 0; text-wrap: balance; letter-spacing: -.01em; }
html[lang="en"] h1, html[lang="en"] h2, html[lang="en"] h3 { font-weight: 600; letter-spacing: -.025em; }
html[lang="zh-CN"] :is(h1, h2, h3, h4, .sub, .lead, .tall) { word-break: keep-all; overflow-wrap: anywhere; }   /* break at punctuation, not mid-word */
p { margin: 0; }
button { font: inherit; color: inherit; -webkit-tap-highlight-color: transparent; }
a { color: inherit; }
:focus-visible { outline: 2px solid var(--accent); outline-offset: 3px; border-radius: 8px; }
[id] { scroll-margin-top: calc(60px + env(safe-area-inset-top, 0px)); }
@keyframes rise { from { transform: translateY(18px); opacity: .001; } to { transform: none; opacity: 1; } }

/* the mark: a sound wave sewn along a seam; the wordmark keeps the seal's serif */
.mark { width: 26px; height: 26px; display: block; flex: none; }

/* header: a thin translucent bar */
header.top { position: sticky; top: env(safe-area-inset-top, 0px); z-index: 9; background: rgba(0, 0, 0, .72); backdrop-filter: saturate(180%) blur(20px); -webkit-backdrop-filter: saturate(180%) blur(20px); border-bottom: 1px solid var(--line); }
header.top .wrap { display: flex; align-items: center; gap: 22px; height: 52px; }
.brand { display: flex; align-items: center; gap: 10px; text-decoration: none; margin-right: auto; }
.brand b { font: 700 16px/1 "Noto Serif SC", "Songti SC", serif; letter-spacing: .14em; }
.brand .en { font: 500 12.5px/1 var(--body); color: var(--mute); }
html[lang="en"] .brand b { display: none; }
html[lang="en"] .brand .en { color: var(--text); font: 600 15px/1 var(--body); letter-spacing: -.01em; }
nav.links { display: flex; gap: 24px; font-size: 13px; }
nav.links a { text-decoration: none; color: var(--mute); transition: color .25s; }
nav.links a:hover { color: var(--text); }
/* the conversation tab: a small sound-creature in headphones, its bubble typing */
.chattab { display: inline-flex; align-items: center; gap: 8px; text-decoration: none; color: var(--text); font: 600 13px/1 var(--body); padding: 4px 14px 4px 6px; border-radius: 999px; background: linear-gradient(90deg, rgba(156, 203, 183, .16), rgba(156, 203, 183, .04)); box-shadow: inset 0 0 0 1px rgba(156, 203, 183, .3); transition: background .25s, transform .25s var(--ease); }
.chattab:hover { transform: translateY(-1px); background: rgba(156, 203, 183, .2); }
.chattab.here { box-shadow: inset 0 0 0 1.5px var(--accent); }
.buddy { width: 38px; height: 30px; flex: none; overflow: visible; animation: bob 3s ease-in-out infinite; }
.buddy .d1, .buddy .d2, .buddy .d3 { animation: type 1.2s ease-in-out infinite; }
.buddy .d2 { animation-delay: .2s; } .buddy .d3 { animation-delay: .4s; }
@keyframes bob { 0%, 100% { transform: translateY(0); } 50% { transform: translateY(-1.5px) rotate(-2deg); } }
@keyframes type { 0%, 60%, 100% { opacity: .25; } 30% { opacity: 1; } }
@media (max-width: 820px) { .chattab span { display: none; } .chattab { padding: 3px 6px; } }
.lang { font: 500 12.5px/1 var(--body); color: var(--mute); text-decoration: none; padding: 7px 10px; border: 1px solid var(--line-2); border-radius: 999px; transition: color .25s, border-color .25s; }
.lang:hover { color: var(--text); border-color: var(--mute); }
@media (max-width: 820px) { nav.links { display: none; } .brand .en { display: none; } html[lang="en"] .brand .en { display: inline; } }

/* buttons and the segmented A/B */
.btn { display: inline-flex; align-items: center; gap: 10px; border-radius: 999px; padding: 14px 24px; font: 500 16px/1 var(--body); text-decoration: none; cursor: pointer; border: 1px solid var(--accent); background: var(--accent); color: #000; transition: transform .25s var(--ease), box-shadow .25s; white-space: nowrap; }
.btn:hover { transform: translateY(-1px); box-shadow: 0 14px 34px -16px rgba(156, 203, 183, .7); }
.btn:active { transform: none; }
.btn:disabled { opacity: .6; cursor: wait; transform: none; }
.btn .arr { transition: transform .25s var(--ease); }
.btn:hover .arr { transform: translateX(3px); }
.btn.small { padding: 8px 14px; font-size: 13px; }
.seg { position: relative; display: inline-grid; grid-template-columns: 1fr 1fr; background: var(--surface-3); border-radius: 999px; padding: 3px; }
.seg .thumb { position: absolute; top: 3px; bottom: 3px; left: 3px; width: calc(50% - 3px); border-radius: 999px; background: var(--accent); transition: transform .45s var(--ease), background .35s; }
.seg.orig .thumb { transform: translateX(100%); background: var(--text); }
.seg button { position: relative; z-index: 1; border: 0; background: none; color: var(--mute); font: 600 15px/1 var(--body); padding: 12px 22px; border-radius: 999px; cursor: pointer; transition: color .3s; min-width: 96px; white-space: nowrap; }
.seg button[aria-pressed="true"] { color: #000; }
@media (max-width: 640px) { .seg button { padding: 11px 16px; min-width: 0; } }

/* sections */
.sec { display: grid; gap: 44px; padding-block: 140px 40px; }
@media (max-width: 860px) { .sec { padding-block: 88px 24px; gap: 28px; } }
.head { display: grid; gap: 14px; max-width: 980px; }
.head.center { text-align: center; justify-items: center; margin-inline: auto; }
.eyebrow { font: 600 14px/1 var(--body); color: var(--accent); letter-spacing: .02em; }
.sec h2 { font-size: clamp(32px, 4.4vw, 56px); line-height: 1.12; }
.sec .sub { color: var(--mute); font-size: clamp(17px, 1.6vw, 21px); line-height: 1.5; max-width: 34em; }
.reveal { transition: transform 1s var(--ease), opacity 1s var(--ease); }
.reveal.pre { transform: translateY(30px); opacity: .001; }

footer { margin-top: 120px; background: var(--surface); }
footer .wrap { padding-block: 28px 40px; display: grid; gap: 18px; font-size: 12px; line-height: 1.6; color: var(--mute); }
footer a { color: var(--mute); text-decoration: none; transition: color .2s; }
footer a:hover { color: var(--text); }
footer .frow { display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 14px 28px; padding-bottom: 18px; border-bottom: 1px solid var(--line); }
footer .fbrand { display: inline-flex; align-items: center; gap: 9px; color: var(--text); }
footer .fbrand .mark { width: 20px; height: 20px; }
footer .fbrand b { font: 700 13px/1 "Noto Serif SC", "Songti SC", serif; letter-spacing: .14em; }
footer .fbrand span { font: 500 12px/1 var(--body); color: var(--mute); }
html[lang="en"] footer .fbrand b { display: none; }
footer .flinks { display: flex; flex-wrap: wrap; gap: 8px 22px; }
footer .note { color: var(--faint); max-width: 72em; }
footer .legal { display: flex; flex-wrap: wrap; gap: 6px 22px; color: var(--faint); }
footer .legal a { color: var(--faint); }

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation: none !important; transition: none !important; scroll-behavior: auto !important; }
  .reveal.pre { transform: none; opacity: 1; }
}