/* 全局 reset、排版、通用小件（按钮、胶囊、入场显现） */
*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-behavior: smooth; }
body {
  margin: 0; background: var(--bg); color: var(--text-1);
  font-family: var(--font-sans); font-size: 16px; line-height: 1.55;
  -webkit-font-smoothing: antialiased; -moz-osx-font-smoothing: grayscale; text-rendering: optimizeLegibility;
  font-feature-settings: 'ss01', 'cv11'; font-optical-sizing: auto;
  overflow-x: hidden;
}
h1, h2, h3, p, dl, dd { margin: 0; }
/* 全页底色层：fixed 在最底下，颜色随滚动插值 */
.backdrop { position: fixed; inset: 0; z-index: -1; background: var(--bg); pointer-events: none; }
h1, h2, h3 { text-wrap: balance; }
p { text-wrap: pretty; }
::selection { background: rgba(166, 203, 242, 0.45); }
button { font: inherit; color: inherit; }
:focus-visible { outline: 2px solid var(--accent); outline-offset: 3px; border-radius: 6px; }
.sr-only { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; }
.skip { position: absolute; left: 12px; top: -48px; z-index: 100; background: var(--text-1); color: #fff; padding: 8px 12px; border-radius: var(--r-sm); text-decoration: none; }
.skip:focus { top: 12px; }
/* 中文正文归零负字距；品牌字标始终保留英文排版。 */
html[lang='zh-CN'] *:not(.brand__word) { letter-spacing: 0 !important; }

/* —— 顶栏 —— */
.nav {
  position: fixed; inset: 0 0 auto 0; z-index: 40; height: 64px;
  display: flex; align-items: center; justify-content: space-between; padding: 0 var(--pad-x);
  background: color-mix(in srgb, var(--bg) 78%, transparent);
  -webkit-backdrop-filter: saturate(1.4) blur(14px); backdrop-filter: saturate(1.4) blur(14px);
  border-bottom: 1px solid transparent; transition: border-color 200ms, background-color 300ms, color 300ms;
}
.nav.is-scrolled { border-bottom-color: var(--border); }
/* 滚到深色段落时顶栏跟着变深，不出现一块突兀的白条 */
.nav.is-dark { background: color-mix(in srgb, var(--night) 72%, transparent); color: var(--night-text); }
.nav.is-dark .lang { color: var(--night-text); border-color: rgba(255,250,240,.16); }
.brand { display: inline-flex; align-items: center; gap: 9px; color: var(--ink); text-decoration: none; font-family: 'Geist', sans-serif; --logo-glint: var(--bg); }
.brand__mark { display: block; flex: none; transition: transform 700ms var(--ease-spring); }
/* 悬停：圆环像弹珠一样滚半圈再停住 */
.brand:hover .brand__mark { transform: rotate(-18deg); }
.brand__word { font-family: 'Geist', sans-serif; font-weight: 640; font-variation-settings: 'wght' 640; font-size: 21px; line-height: 1; letter-spacing: -0.045em; padding-bottom: 1px; font-feature-settings: 'ss01'; }
.nav.is-dark .brand { color: var(--night-text); --logo-glint: var(--dusk); }
.nav__right { display: flex; align-items: center; gap: 10px; }
.lang {
  height: 32px; padding: 0 12px; border-radius: var(--r-full); border: 1px solid var(--border-strong);
  background: transparent; cursor: pointer; font-size: 13px; font-weight: 500; transition: background-color 120ms;
}
.lang { transition: background-color 160ms, transform 420ms var(--ease-spring); }
.lang:hover { background: color-mix(in srgb, currentColor 6%, transparent); }
.lang:active { transform: scale(.95); }
.language-menu { position: relative; }
.lang--menu { display: inline-flex; align-items: center; gap: 6px; padding: 0 10px; }
.lang__globe, .lang__chevron { stroke: currentColor; stroke-width: 1.3; stroke-linecap: round; stroke-linejoin: round; flex: none; }
.lang__chevron { transition: transform 180ms; }
.lang--menu[aria-expanded='true'] .lang__chevron { transform: rotate(180deg); }
.lang__options { position: absolute; top: calc(100% + 9px); right: 0; width: 132px; padding: 5px; display: grid; gap: 2px; border: 1px solid var(--border-strong); border-radius: 12px; background: var(--bg-2); color: var(--text-1); box-shadow: var(--shadow-2); }
.lang__options[hidden] { display: none; }
.lang__options button { display: flex; align-items: center; justify-content: space-between; min-height: 40px; padding: 8px 10px; border: 0; border-radius: 7px; background: transparent; text-align: left; font-size: 13px; cursor: pointer; }
.lang__options button:hover, .lang__options button:focus-visible { background: rgba(28,25,20,.06); }
.lang__options button span { visibility: hidden; }
.lang__options button[aria-checked='true'] span { visibility: visible; }
.nav.is-dark .lang__options { background: var(--night); color: var(--night-text); border-color: rgba(255,250,240,.16); }
.nav.is-dark .lang__options button:hover, .nav.is-dark .lang__options button:focus-visible { background: rgba(255,250,240,.08); }

/* 顶栏入口：首屏胶囊还在视野里时藏起来，滚过首屏才出现；和首屏同一个叫法 */
.nav__invite { display: inline-flex; align-items: center; height: 34px; padding: 0 15px; margin-right: 2px; border-radius: var(--r-full); background: var(--ink); color: #F6F4EF; font-size: 13px; font-weight: 560; text-decoration: none; white-space: nowrap;
  opacity: 0; visibility: hidden; transform: translateY(-4px); pointer-events: none;
  transition: opacity 240ms var(--ease-out), transform 420ms var(--ease-spring), visibility 0s linear 240ms, background-color 300ms, color 300ms; }
.nav.has-cta .nav__invite { opacity: 1; visibility: visible; transform: none; pointer-events: auto; transition-delay: 0s; }
.nav__invite:hover { background: #33323a; }
.nav.is-dark .nav__invite { background: var(--night-text); color: var(--night); }
.nav__invite-short { display: none; }
@media (max-width: 420px) { .nav__invite-long { display: none; } .nav__invite-short { display: inline; } }

.btn {
  position: relative; display: inline-flex; align-items: center; gap: 11px; height: 50px; padding: 0 22px 0 18px; border: 0; border-radius: var(--r-full);
  font-size: 15px; font-weight: 560; letter-spacing: -0.01em; cursor: pointer; isolation: isolate;
  transition: transform 520ms var(--ease-spring), box-shadow 300ms var(--ease-out), background-color 160ms;
}
.btn--primary {
  background: linear-gradient(180deg, #2a2a31, var(--ink) 55%); color: #F6F4EF;
  box-shadow: 0 1px 0 rgba(255,255,255,.12) inset, 0 -1px 0 rgba(0,0,0,.4) inset, 0 10px 24px -10px rgba(20,18,15,.55), 0 2px 4px rgba(20,18,15,.12);
}
.btn--primary:hover { transform: translateY(-1.5px); box-shadow: 0 1px 0 rgba(255,255,255,.14) inset, 0 -1px 0 rgba(0,0,0,.4) inset, 0 16px 30px -12px rgba(20,18,15,.55), 0 3px 6px rgba(20,18,15,.12); }
.btn:active { transform: translateY(0) scale(0.97); transition-duration: 140ms; }
.btn[aria-disabled='true'] { cursor: default; }
.btn[aria-disabled='true'] .btn__pen::after { opacity: 1; }
/* 按钮里的小闪光笔：石墨笔身 + 金属笔尖；hover 时笔转一点、笔尖亮起，暗示「按下会闪」 */
.btn__pen { position: relative; width: 22px; height: 5px; border-radius: 3px; transform: rotate(-32deg); transition: transform 520ms var(--ease-spring);
  background: linear-gradient(90deg, #4c4e57 0 70%, #c9ccd4 70% 76%, #3a3c44 76% 86%, #e9ebef 86%); box-shadow: 0 0 0 .5px rgba(255,255,255,.15); }
.btn__pen::after { content: ''; position: absolute; right: -5px; top: 50%; width: 12px; height: 12px; margin-top: -6px; border-radius: 50%;
  background: radial-gradient(circle, #fff 0 22%, rgba(220,235,255,.6) 45%, rgba(255,255,255,0) 70%); opacity: 0; transform: scale(.4); transition: opacity 260ms var(--ease-out), transform 420ms var(--ease-spring); }
.btn:hover .btn__pen, .pen-link:hover .btn__pen { transform: rotate(-44deg) translateX(1px); }
.btn:hover .btn__pen::after, .pen-link:hover .btn__pen::after { opacity: 1; transform: scale(1); }
.pen-link[aria-disabled='true'] .btn__pen::after { opacity: 1; }

/* 进入视口时显现：上移 + 淡入；.reveal 由 IntersectionObserver 加 .is-in */
.reveal { opacity: 0; transform: translateY(24px); transition: opacity 900ms var(--ease-out-soft), transform 1100ms var(--ease-out); transition-delay: var(--d, 0ms); }
.reveal.is-in { opacity: 1; transform: none; }

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .reveal { opacity: 1; transform: none; transition: none; }
  *, *::before, *::after { animation-duration: 0.01ms !important; animation-iteration-count: 1 !important; transition-duration: 0.01ms !important; }
  .intro, .line__in { opacity: 1 !important; transform: none !important; }
}

/* 通用弹珠：外层管高光和投影（不转），内层 i 管颜色和花纹（滚动时转）。尺寸用 --s */
.mb { --s: 16px; position: absolute; width: var(--s); height: var(--s); border-radius: 50%; display: block;
  background: radial-gradient(circle at 34% 28%, rgba(255,255,255,.95) 0 7%, rgba(255,255,255,0) 26%), radial-gradient(circle at 62% 86%, rgba(255,255,255,.28), transparent 42%);
  box-shadow: 0 2px 3px -1px rgba(20,18,15,.35), inset 0 -1px 3px rgba(0,0,0,.16); z-index: 0; }
.mb > i { position: absolute; inset: 0; border-radius: 50%; z-index: -1; display: block;
  background: conic-gradient(from 20deg, transparent 0 12%, rgba(255,255,255,.24) 14% 18%, transparent 20% 62%, rgba(255,255,255,.16) 64% 67%, transparent 69%), radial-gradient(circle at 40% 35%, var(--cl), var(--c) 55%, var(--cd)); }