/* PaperEcho 纸上回声 — 与从头到脚同一套版式：纸面底、细线分区、零阴影。 */

:root {
  --bg: #F6F5F1;
  --bg-veil: rgba(246, 245, 241, .86);
  --surface: #EFEEE9;
  --ink: #171715;
  --ink-2: #5A5A55;
  --ink-3: #686862;
  --hair: rgba(23, 23, 21, .14);
  --hair-2: rgba(23, 23, 21, .26);
  --signal: #171715;
  --on-signal: #F6F5F1;
  --accent: #1B5E54;
  --accent-soft: rgba(27, 94, 84, .12);

  --sans: -apple-system, BlinkMacSystemFont, "PingFang SC", "Hiragino Sans GB",
          "Source Han Sans SC", "Noto Sans SC", "Microsoft YaHei", system-ui, sans-serif;
  --serif: ui-serif, "Iowan Old Style", "Palatino Linotype", "Songti SC",
           "Source Han Serif SC", "Noto Serif SC", "Times New Roman", serif;
  --mono: ui-monospace, "SF Mono", SFMono-Regular, Menlo, Consolas, monospace;

  --maxw: 1120px;
  --gutter: clamp(20px, 5vw, 56px);
  --step: clamp(64px, 9vw, 112px);
  --radius: 4px;
  --ease: cubic-bezier(.22, .61, .36, 1);
  --dur: 240ms;
  --reveal: 620ms;
}

:root[data-theme="dark"] {
  --bg: #0E0E0F;
  --bg-veil: rgba(14, 14, 15, .86);
  --surface: #171718;
  --ink: #ECECE8;
  --ink-2: #A8A8A2;
  --ink-3: #85857F;
  --hair: rgba(236, 236, 232, .14);
  --hair-2: rgba(236, 236, 232, .26);
  --signal: #ECECE8;
  --on-signal: #0E0E0F;
  --accent: #6FBFAE;
  --accent-soft: rgba(111, 191, 174, .16);
}

*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-behavior: smooth; }
body {
  margin: 0; background: var(--bg); color: var(--ink);
  font-family: var(--sans); font-size: 16.5px; line-height: 1.75;
  -webkit-font-smoothing: antialiased;
}
::selection { background: var(--signal); color: var(--on-signal); }
:focus-visible { outline: 2px solid var(--signal); outline-offset: 3px; }
a { color: inherit; text-decoration: none; }
a:hover { text-decoration: underline; text-underline-offset: .2em; text-decoration-thickness: 1px; }
button { font: inherit; color: inherit; }
h1, h2, h3, p, dl, dd, dt, ol, ul, figure { margin: 0; }
ol, ul { padding: 0; list-style: none; }
img, video { display: block; max-width: 100%; }

.wrap { width: 100%; max-width: var(--maxw); margin: 0 auto; padding: 0 var(--gutter); }
.skip { position: absolute; top: 0; left: var(--gutter); z-index: 60; padding: 10px 16px; background: var(--signal); color: var(--on-signal); border-radius: var(--radius); clip-path: inset(50%); transform: translateY(-200%); }
.skip:focus { clip-path: none; transform: none; }

/* 顶栏 */
.site-head {
  position: sticky; top: 0; z-index: 30; background: var(--bg-veil);
  border-bottom: 1px solid transparent; transition: border-color var(--dur) var(--ease);
}
.site-head[data-stuck] { border-bottom-color: var(--hair); }
@supports (backdrop-filter: blur(12px)) { .site-head { backdrop-filter: blur(12px); } }
.head-in { display: flex; align-items: center; gap: 28px; min-height: 64px; }
.brand { display: flex; align-items: baseline; gap: 10px; flex: none; }
.brand-en { font-family: var(--serif); font-size: 19px; font-weight: 500; letter-spacing: -.01em; }
.brand-cn { color: var(--ink-2); font-size: 12px; letter-spacing: .16em; }
.nav { display: flex; gap: 24px; margin-left: auto; color: var(--ink-2); font-size: 14px; }
.nav a:hover { color: var(--ink); text-decoration: none; }
.head-actions { display: flex; align-items: center; gap: 10px; margin-left: 8px; }
.theme, .btn {
  display: inline-flex; align-items: center; justify-content: center;
  min-height: 36px; padding: 0 12px; border: 1px solid var(--hair-2);
  background: transparent; border-radius: var(--radius); font-size: 13px;
  cursor: pointer; transition: background var(--dur) var(--ease), color var(--dur) var(--ease), border-color var(--dur) var(--ease);
}
.theme:hover { border-color: var(--ink-3); }
.btn { min-height: 46px; padding: 0 20px; font-size: 14px; font-weight: 600; }
.btn:hover { text-decoration: none; }
.btn-solid { background: var(--signal); color: var(--on-signal); border-color: var(--signal); }
.btn-solid:hover { background: transparent; color: var(--ink); border-color: var(--ink); }
.btn-line { color: var(--ink); }
.btn-line:hover { border-color: var(--ink); }
.btn-small { min-height: 36px; padding: 0 12px; font-size: 13px; }

/* 首屏 */
.hero { display: grid; grid-template-columns: minmax(0, 7fr) minmax(0, 5fr); gap: clamp(32px, 5vw, 72px); align-items: end; padding-block: clamp(64px, 10vw, 128px) var(--step); }
.wordmark-en { font-family: var(--serif); font-size: clamp(54px, 10vw, 128px); font-weight: 500; line-height: .9; letter-spacing: -.04em; }
.wordmark-cn { margin-top: 14px; font-family: var(--serif); font-size: clamp(20px, 2.2vw, 28px); font-weight: 500; letter-spacing: .34em; color: var(--ink-2); }
.hero-line { margin-top: clamp(36px, 6vw, 64px); max-width: 12em; font-size: clamp(28px, 3.8vw, 48px); line-height: 1.2; font-weight: 600; letter-spacing: -.02em; text-wrap: balance; }
.hero-intro { margin-top: 18px; max-width: 34em; color: var(--ink-2); font-size: clamp(16px, 1.4vw, 18px); }
.hero-actions { display: flex; flex-wrap: wrap; gap: 12px; margin-top: 30px; }
.hero-figure { position: relative; border-top: 1px solid var(--hair); padding-top: 18px; }
.hero-figure img { width: 100%; height: auto; border: 1px solid var(--hair); }
.hero-figure figcaption { margin-top: 10px; color: var(--ink-3); font-size: 12px; line-height: 1.6; }
.shot img { width: 100%; height: auto; border: 1px solid var(--hair-2); background: #0B0C0D; }
.shot figcaption { margin-top: 10px; color: var(--ink-3); font-size: 12px; line-height: 1.6; }
.facts { display: grid; grid-template-columns: repeat(5, minmax(0, 1fr)); gap: 0; margin-top: clamp(44px, 7vw, 76px); border-top: 1px solid var(--hair); }
.facts div { padding: 13px 12px 13px 0; border-right: 1px solid var(--hair); }
.facts div:last-child { border-right: 0; }
.facts dt { color: var(--ink-3); font-size: 11px; letter-spacing: .04em; }
.facts dd { margin-top: 3px; font-family: var(--mono); font-size: 12px; letter-spacing: .02em; }


/* 区块 */
.section { padding-block: var(--step); border-top: 1px solid var(--hair); }
.section-head { display: grid; grid-template-columns: minmax(0, 4fr) minmax(0, 7fr); gap: clamp(20px, 4vw, 56px); margin-bottom: clamp(34px, 5vw, 56px); }
.section-head h2 { font-size: clamp(26px, 3vw, 38px); line-height: 1.2; font-weight: 600; letter-spacing: -.02em; }
.section-head p { max-width: 38em; color: var(--ink-2); font-size: 15px; line-height: 1.8; }
.rows { border-top: 1px solid var(--hair); }
.row { display: grid; grid-template-columns: minmax(100px, 2fr) minmax(0, 4fr) minmax(0, 5fr); gap: clamp(16px, 3vw, 40px); padding: 26px 0; border-bottom: 1px solid var(--hair); }
.row-k { color: var(--ink-3); font-size: 12px; letter-spacing: .06em; }
.row h3 { font-size: 18px; line-height: 1.35; font-weight: 600; }
.row p:last-child { color: var(--ink-2); font-size: 14px; line-height: 1.78; }
.steps { border-top: 1px solid var(--hair); }
.steps li { display: grid; grid-template-columns: 3em minmax(140px, 3fr) minmax(0, 6fr); gap: clamp(14px, 3vw, 36px); padding: 24px 0; border-bottom: 1px solid var(--hair); }
.steps span { color: var(--accent); font-family: var(--mono); font-size: 12px; }
.steps h3 { font-size: 17px; line-height: 1.4; font-weight: 600; }
.steps p { color: var(--ink-2); font-size: 14px; }

/* 下载 */
.download { display: grid; grid-template-columns: minmax(0, 7fr) minmax(0, 5fr); gap: clamp(32px, 5vw, 72px); padding-block: var(--step); border-top: 1px solid var(--hair); }
.download h2 { font-size: clamp(30px, 4.6vw, 58px); line-height: 1.12; font-weight: 600; letter-spacing: -.03em; }
.download-copy > p { margin-top: 18px; max-width: 34em; color: var(--ink-2); font-size: 15px; }
.download-copy .small { margin-top: 20px; color: var(--ink-3); font-size: 12px; line-height: 1.7; }
.download-facts { border-top: 1px solid var(--hair); align-self: start; }
.download-facts div { display: flex; justify-content: space-between; gap: 18px; padding: 10px 0; border-bottom: 1px solid var(--hair); }
.download-facts dt { color: var(--ink-3); font-size: 12px; }
.download-facts dd { font-family: var(--mono); font-size: 12px; text-align: right; overflow-wrap: anywhere; }
.download-facts .sha { max-width: 22em; color: var(--ink-3); }

/* 页脚 */
.site-foot { display: grid; grid-template-columns: minmax(0, 5fr) minmax(0, 5fr) minmax(0, 2fr); gap: 28px; padding-top: 48px; padding-bottom: 48px; border-top: 1px solid var(--hair); align-items: start; }
.foot-brand { font-family: var(--serif); font-size: 22px; font-weight: 500; }
.foot-brand span { color: var(--ink-3); font-family: var(--sans); font-size: 12px; letter-spacing: .12em; margin-left: 8px; }
.foot-meta { margin-top: 14px; color: var(--ink-2); font-size: 12px; line-height: 1.8; }
.foot-links { display: grid; gap: 8px; font-size: 13px; }
.foot-links a { color: var(--ink-2); }
.foot-base { color: var(--ink-3); font-size: 11px; text-align: right; }

/* 影片 */
.film { width: min(100% - 32px, 960px); padding: 0; border: 1px solid var(--hair-2); border-radius: var(--radius); background: var(--bg); color: var(--ink); }
.film::backdrop { background: rgba(0, 0, 0, .62); }
.film-head { display: flex; align-items: center; justify-content: space-between; gap: 16px; padding: 14px 16px; border-bottom: 1px solid var(--hair); }
.film-head h2 { font-size: 14px; font-weight: 600; }
.film-close { border: 0; background: transparent; color: var(--ink-3); font-size: 12px; cursor: pointer; }
.film-close:hover { color: var(--ink); }
.film video { width: 100%; height: auto; background: #000; }

/* 入场 */
.js .reveal { opacity: 0; transform: translateY(12px); transition: opacity var(--reveal) var(--ease), transform var(--reveal) var(--ease); }
.js .reveal.shown { opacity: 1; transform: none; }

@media (max-width: 900px) {
  .hero, .download { grid-template-columns: 1fr; }
  .hero { align-items: start; }
  .hero-figure { max-width: 560px; }
  .facts { grid-template-columns: repeat(3, 1fr); }
  .facts div:nth-child(3) { border-right: 0; }
  .facts div:nth-child(n+4) { border-top: 1px solid var(--hair); }
  .row { grid-template-columns: 1fr; gap: 6px; }
  .steps li { grid-template-columns: 2.4em 1fr; }
  .steps p { grid-column: 2; }
  .site-foot { grid-template-columns: 1fr 1fr; }
  .foot-base { grid-column: 1 / -1; text-align: left; }
}
@media (max-width: 700px) {
  .nav { display: none; }
  .head-actions { margin-left: auto; }
  .head-actions .btn { display: none; }
  .section-head { grid-template-columns: 1fr; gap: 10px; }
  .hero-line { font-size: 30px; }
  .facts { grid-template-columns: 1fr 1fr; }
  .facts div:nth-child(2n) { border-right: 0; }
  .facts div:nth-child(n+3) { border-top: 1px solid var(--hair); }
  .site-foot { grid-template-columns: 1fr; }
  .foot-base { grid-column: auto; }
  .download-facts dd { max-width: 60%; }
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation-duration: 1e-05s !important; transition-duration: 1e-05s !important; }
  .js .reveal { opacity: 1; transform: none; }
}