@import url('https://fonts.googleapis.com/css2?family=DM+Sans:wght@400;500;600;700&family=Noto+Sans+SC:wght@400;500;600;700;800;900&display=swap');

:root {
  --blue: #2347ef;
  --ink: #171a21;
  --muted: #626772;
  --line: #d9dce3;
  --lime: #daff75;
  --paper: #fafbfc;
}

* { box-sizing: border-box; }

html {
  scroll-behavior: smooth;
  scroll-padding-top: 90px;
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: 'DM Sans', 'Noto Sans SC', sans-serif;
  font-size: 16px;
  line-height: 1.65;
}

html[data-language="zh"] body {
  font-family: 'Noto Sans SC', 'DM Sans', sans-serif;
}

html[data-language="en"] .zh,
html[data-language="zh"] .en { display: none !important; }

a { color: inherit; text-decoration: none; }
button, a, summary { -webkit-tap-highlight-color: transparent; }
button { font: inherit; }
a:focus-visible, button:focus-visible, summary:focus-visible {
  outline: 3px solid #ff7b39;
  outline-offset: 5px;
}

header {
  height: 94px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 25px;
  padding: 0 5%;
  background: var(--paper);
}

.brand {
  display: flex;
  align-items: center;
  flex: 0 0 auto;
  gap: 10px;
  font-size: 29px;
  font-weight: 700;
  letter-spacing: -1.4px;
}

.os { font-weight: 400; }

.brandmark {
  position: relative;
  width: 32px;
  height: 32px;
  background: var(--ink);
  color: white;
  font-size: 24px;
  line-height: 32px;
  letter-spacing: 0;
  text-align: center;
}

.brandmark span {
  position: absolute;
  top: -7px;
  right: -5px;
  background: var(--paper);
  color: var(--blue);
  font-size: 17px;
  line-height: 18px;
}

nav {
  display: flex;
  gap: 34px;
  font-size: 14px;
}

nav a:hover, .nav-end:hover { color: var(--blue); }

.header-actions {
  display: flex;
  align-items: center;
  flex: 0 0 auto;
  gap: 24px;
}

.language-switch {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  min-height: 38px;
  padding: 7px 11px;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: white;
  color: var(--ink);
  cursor: pointer;
  font-size: 14px;
  font-weight: 600;
  transition: border-color .2s, color .2s, transform .2s;
}

.language-switch:hover {
  border-color: var(--blue);
  color: var(--blue);
  transform: translateY(-1px);
}

.language-switch__mark {
  display: grid;
  place-items: center;
  width: 22px;
  height: 22px;
  border-radius: 50%;
  background: var(--blue);
  color: white;
  font-size: 12px;
  font-weight: 700;
}

.nav-end {
  padding: 6px 0;
  border-bottom: 1px solid var(--ink);
  font-size: 14px;
}

.nav-end span { margin-left: 20px; }

.hero {
  padding: 26px 5% 0;
  background: var(--blue);
  color: white;
}

.hero-top, .hero-bottom {
  display: flex;
  justify-content: space-between;
  gap: 15px;
  font-size: 12px;
  letter-spacing: 1.5px;
}

.hero-top {
  padding-bottom: 24px;
  border-bottom: 1px solid #ffffff42;
}

.hero-content {
  display: grid;
  grid-template-columns: 1.45fr 1fr;
  gap: 70px;
  padding: 55px 0 62px;
}

.eyebrow {
  margin: 0 0 21px;
  color: #d4dcff;
  font-size: 13px;
  letter-spacing: 2px;
}

h1 {
  margin: 0;
  font-size: clamp(58px, 6.8vw, 103px);
  font-weight: 700;
  line-height: 1.06;
  letter-spacing: -4px;
}

.period { color: var(--lime); }
html[data-language="zh"] h1 { line-height: 1.17; }

.hero-aside {
  align-self: end;
  justify-self: end;
  width: 100%;
  max-width: 340px;
  padding-bottom: 7px;
}

.revision {
  display: flex;
  justify-content: space-between;
  padding: 13px 0;
  border-top: 1px solid #ffffff65;
  border-bottom: 1px solid #ffffff65;
  font-size: 12px;
  letter-spacing: 1px;
}

.question {
  margin: 24px 0 12px;
  font-size: 30px;
  font-weight: 500;
  line-height: 1.45;
}

.button {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  margin-top: 29px;
  padding: 16px 20px;
  background: var(--lime);
  color: var(--ink);
  font-weight: 600;
  transition: background .2s;
}

.button:hover { background: white; }
.button span { font-size: 18px; font-weight: 400; }

.hero-text-link {
  display: inline-block;
  margin-top: 17px;
  padding-bottom: 4px;
  border-bottom: 1px solid #ffffff73;
  color: white;
  font-size: 14px;
}

.hero-text-link:hover { border-bottom-color: white; }

.hero-bottom {
  padding: 21px 0;
  border-top: 1px solid #ffffff42;
}

.section {
  padding: 92px 5%;
  border-bottom: 1px solid var(--line);
}

.section-kicker {
  margin: 0 0 28px;
  color: var(--muted);
  font-size: 12px;
  line-height: 1.8;
  letter-spacing: 1.3px;
}

h2 {
  margin: 0 0 14px;
  font-size: clamp(29px, 3vw, 44px);
  font-weight: 600;
  line-height: 1.36;
  letter-spacing: -1px;
}

h3, p { overflow-wrap: break-word; }

.intro {
  display: grid;
  grid-template-columns: 1fr 2fr;
  gap: 50px;
}

.intro-detail {
  max-width: 760px;
  margin-top: 30px;
}

.intro-detail p {
  margin: 0;
  color: var(--muted);
  font-size: 17px;
}

.principles {
  display: grid;
  grid-template-columns: 1fr 1.45fr;
  gap: 70px;
}

.principle-list article {
  display: flex;
  gap: 25px;
  padding: 27px 0 35px;
  border-top: 1px solid var(--ink);
}

.number {
  padding-top: 5px;
  color: var(--blue);
  font-size: 14px;
}

.principle-list h3 {
  margin: 0 0 15px;
  font-size: 26px;
  font-weight: 600;
  line-height: 1.35;
}

.principle-list p {
  margin: 9px 0;
  color: var(--muted);
}

.symbol {
  margin-left: auto;
  color: var(--blue);
  font-size: 35px;
}

.power-equation {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px 11px;
  margin-top: 14px;
  padding: 22px;
  border: 1px solid var(--ink);
  background: #f3f4f7;
  font-size: 14px;
  font-weight: 600;
}

.power-equation b { color: var(--blue); font-weight: 500; }
.power-equation strong {
  margin-left: auto;
  padding: 5px 9px;
  background: var(--ink);
  color: white;
  font-size: 12px;
  letter-spacing: .4px;
  text-transform: uppercase;
}

.equation-note {
  margin: 12px 0 0;
  color: var(--muted);
  font-size: 14px;
}

.framework {
  display: grid;
  grid-template-columns: 1fr 1.3fr;
  gap: 90px;
  background: var(--ink);
  color: white;
}

.framework .section-kicker { color: #aeb5c4; }

.framework-note {
  max-width: 390px;
  margin-top: 48px;
  color: #aeb5c4;
}

.layers article {
  padding: 20px 0 22px;
  border-top: 1px solid #52565e;
}

.layers article:last-child { border-bottom: 1px solid #52565e; }

.layer-label {
  display: flex;
  justify-content: space-between;
  color: var(--lime);
  font-size: 12px;
  letter-spacing: 1px;
}

.layers h3 {
  margin: 15px 0 5px;
  font-size: 25px;
  font-weight: 500;
}

.layers p {
  max-width: 480px;
  margin: 0;
  color: #aeb5c4;
}

.experiments {
  display: grid;
  grid-template-columns: 1fr 1.45fr;
  gap: 50px 70px;
}

.chess {
  padding: 32px;
  border: 1px solid var(--line);
  background: white;
}

.experiment-meta {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 12px;
  font-size: 12px;
  letter-spacing: .3px;
}

.tag {
  padding: 5px 9px;
  background: #edf0ff;
  color: #203fc9;
  font-size: 12px;
}

.chess h3 {
  margin: 29px 0 12px;
  font-size: 34px;
  font-weight: 600;
  line-height: 1.3;
  letter-spacing: -1px;
}

.chess > p {
  margin: 14px 0;
  color: var(--muted);
}

.arms {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 12px;
  margin: 27px 0 16px;
  padding: 20px 0;
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
}

.arms div { font-size: 14px; }
.arms div > span:first-child {
  display: block;
  margin-bottom: 8px;
  color: var(--blue);
  font-size: 22px;
}
.arms div > span:last-child { display: block; line-height: 1.35; }

summary {
  position: relative;
  padding: 16px 28px 16px 0;
  cursor: pointer;
  list-style: none;
  font-size: 16px;
}

summary::-webkit-details-marker { display: none; }
summary::after {
  content: '+';
  position: absolute;
  top: 17px;
  right: 0;
  color: var(--blue);
  font-size: 22px;
  line-height: 1;
}
details[open] > summary::after { content: '−'; }
details p { color: var(--muted); font-size: 15px; }

.small-experiments {
  display: grid;
  grid-column: 2;
  grid-template-columns: 1fr 1fr;
  gap: 32px;
}

.small-experiments h3 {
  margin: 13px 0;
  font-size: 21px;
  font-weight: 500;
  line-height: 1.4;
}

.small-experiments .section-kicker {
  font-size: 12px;
  letter-spacing: .4px;
}

.small-experiments p { color: var(--muted); font-size: 15px; }

.revisions {
  display: grid;
  grid-template-columns: .8fr 1.7fr;
  gap: 70px;
  background: #f3f4f7;
}

.revision-heading > p:last-child {
  max-width: 420px;
  margin-top: 24px;
  color: var(--muted);
}

.revision-table { border-top: 2px solid var(--ink); }

.revision-row {
  display: grid;
  grid-template-columns: 1fr 1fr 1.15fr;
  gap: 22px;
  padding: 20px 0;
  border-bottom: 1px solid #cfd2d9;
}

.revision-row span { font-size: 14px; }
.revision-row span:first-child { color: #8a4a47; text-decoration: line-through; }
.revision-row span:nth-child(2) { color: var(--ink); font-weight: 600; }
.revision-row span:last-child { color: var(--muted); }
.revision-row--head { padding: 10px 0; }
.revision-row--head span {
  color: var(--muted) !important;
  font-size: 11px;
  font-weight: 600 !important;
  letter-spacing: 1px;
  text-decoration: none !important;
  text-transform: uppercase;
}

.question-layout {
  display: grid;
  grid-template-columns: 1fr 1.45fr;
  gap: 70px;
}

.question-layout > div:first-child > p {
  max-width: 385px;
  color: var(--muted);
}

.question-items details {
  padding: 8px 0;
  border-top: 1px solid var(--line);
}

.question-items details:last-child { border-bottom: 1px solid var(--line); }
.question-items summary { font-size: 20px; }
.question-items details p { padding-right: 26px; }

.closing {
  display: grid;
  grid-template-columns: 1.2fr 1fr 1fr;
  align-items: center;
  gap: 35px;
  padding: 70px 5%;
  background: var(--lime);
}

.closing > p:first-child {
  font-size: 29px;
  font-weight: 500;
  letter-spacing: -.8px;
}

.closing > p:nth-child(2) {
  color: #364220;
  font-size: 21px;
  line-height: 1.35;
}

.closing a {
  justify-self: end;
  padding-bottom: 13px;
  border-bottom: 1px solid var(--ink);
  font-size: 20px;
}

.closing a span {
  display: block;
  margin-top: 8px;
  font-size: 14px;
}

footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 25px;
  padding: 40px 5%;
  font-size: 13px;
}

footer p { margin: 0; }
footer > span { text-align: right; }
.footer-paper { border-bottom: 1px solid var(--ink); }

.skip {
  position: fixed;
  z-index: 5;
  top: -100px;
  left: 15px;
  padding: 10px;
  background: white;
}

.skip:focus { top: 12px; }

@media (min-width: 1600px) {
  header, .hero, .section, .closing, footer {
    padding-left: calc((100vw - 1440px) / 2);
    padding-right: calc((100vw - 1440px) / 2);
  }
}

@media (max-width: 1100px) {
  nav { gap: 22px; }
  .header-actions { gap: 14px; }
  .nav-end { display: none; }
  .hero-content { gap: 35px; }
  .hero-aside { max-width: 300px; }
  h1 { letter-spacing: -2px; }
  .intro, .principles, .framework, .experiments, .revisions, .question-layout { gap: 35px; }
  .intro { grid-template-columns: 1fr 2fr; }
  .closing { grid-template-columns: 1fr 1fr; }
  .closing a { grid-column: 2; }
  .small-experiments { gap: 20px; }
  .chess { padding: 23px; }
  .hero-top span:last-child { max-width: 240px; text-align: right; }
}

@media (max-width: 760px) {
  header {
    height: auto;
    min-height: 83px;
    flex-wrap: wrap;
    gap: 14px;
    padding: 18px 6%;
  }
  .brand { font-size: 26px; }
  .brandmark { width: 28px; height: 28px; line-height: 28px; }
  .header-actions { margin-left: auto; }
  .language-switch { min-height: 36px; padding: 6px 10px; }
  nav {
    order: 3;
    width: 100%;
    justify-content: space-between;
    gap: 15px;
    padding-top: 11px;
    border-top: 1px solid var(--line);
  }
  .hero { padding: 22px 6% 0; }
  .hero-top { font-size: 12px; letter-spacing: .2px; }
  .hero-top span:last-child { display: none; }
  .hero-content {
    grid-template-columns: 1fr;
    gap: 36px;
    padding: 38px 0;
  }
  h1 { font-size: clamp(49px, 13vw, 76px); line-height: 1.08; }
  .hero-aside { justify-self: start; max-width: none; }
  .question { margin: 18px 0 12px; font-size: 23px; line-height: 1.5; }
  .question br { display: none; }
  .revision { padding: 10px 0; }
  .button { margin-top: 20px; }
  .hero-bottom {
    flex-direction: column;
    gap: 4px;
    font-size: 12px;
    letter-spacing: .4px;
  }
  .hero-bottom span:last-child { font-size: 12px; }
  .section { padding: 56px 6%; }
  .intro, .principles, .framework, .experiments, .revisions, .question-layout {
    grid-template-columns: 1fr;
    gap: 28px;
  }
  .intro > .section-kicker { margin: 0; }
  .intro-detail { margin-top: 25px; }
  .principle-list article { gap: 15px; }
  .principle-list h3 { font-size: 23px; }
  .symbol { font-size: 28px; }
  .framework-note { margin-top: 25px; }
  .layers h3 { font-size: 23px; }
  .chess h3 { font-size: 29px; }
  .small-experiments {
    grid-column: auto;
    grid-template-columns: 1fr;
    gap: 18px;
  }
  .small-experiments article {
    padding-top: 23px;
    border-top: 1px solid var(--line);
  }
  .revision-row {
    grid-template-columns: 1fr;
    gap: 7px;
  }
  .revision-row--head { display: none; }
  .revision-row span:first-child::before,
  .revision-row span:nth-child(2)::before,
  .revision-row span:last-child::before {
    display: block;
    margin-bottom: 3px;
    color: var(--muted);
    font-size: 10px;
    font-weight: 600;
    letter-spacing: .8px;
    text-decoration: none;
    text-transform: uppercase;
  }
  .revision-row span:first-child::before { content: 'FORMER'; }
  .revision-row span:nth-child(2)::before { content: 'CURRENT'; }
  .revision-row span:last-child::before { content: 'WHY'; }
  html[data-language="zh"] .revision-row span:first-child::before { content: '原主张'; }
  html[data-language="zh"] .revision-row span:nth-child(2)::before { content: '现立场'; }
  html[data-language="zh"] .revision-row span:last-child::before { content: '原因'; }
  .experiment-heading .section-kicker { margin-bottom: 20px; }
  .closing {
    grid-template-columns: 1fr;
    gap: 4px;
    padding: 38px 6%;
  }
  .closing > p:first-child { margin: 0; font-size: 26px; }
  .closing > p:nth-child(2) { font-size: 20px; }
  .closing a {
    grid-column: auto;
    justify-self: start;
    margin-top: 18px;
  }
  footer { flex-wrap: wrap; gap: 24px; padding: 32px 6%; }
  footer > .brand { width: 100%; }
  footer > span { text-align: left; }
  .arms { gap: 8px; }
  .arms div { font-size: 13px; }
  .chess { padding: 22px 18px; }
}

@media (max-width: 430px) {
  nav { justify-content: flex-start; gap: 12px 18px; font-size: 13px; }
  .language-switch__mark { display: none; }
  .language-switch { padding-inline: 12px; }
  .hero-top { font-size: 11px; }
  .arms { grid-template-columns: 1fr; }
  .arms div {
    display: grid;
    grid-template-columns: 28px 1fr;
    align-items: center;
    gap: 10px;
  }
  .arms div > span:first-child { margin: 0; }
}

/* White paper */
.paper-header {
  position: sticky;
  z-index: 20;
  top: 0;
  min-height: 76px;
  height: auto;
  border-bottom: 1px solid var(--line);
  background: rgba(250, 251, 252, .95);
  backdrop-filter: blur(12px);
}

.paper-header .paper-nav {
  margin-left: auto;
}

.paper-main { background: var(--paper); }

.paper-hero {
  padding: 72px 5% 66px;
  border-bottom: 1px solid var(--line);
  background: var(--ink);
  color: white;
}

.paper-hero__inner,
.paper-shell {
  width: min(100%, 1280px);
  margin: 0 auto;
}

.paper-hero__meta {
  display: flex;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 12px;
  color: #aeb5c4;
  font-size: 12px;
  letter-spacing: 1.2px;
  text-transform: uppercase;
}

.paper-hero h1 {
  max-width: 1050px;
  margin-top: 42px;
  font-size: clamp(46px, 7vw, 96px);
}

.paper-hero .paper-deck {
  max-width: 760px;
  margin: 30px 0 0 auto;
  color: #d5d9e2;
  font-size: clamp(19px, 2vw, 27px);
  line-height: 1.5;
}

.paper-shell {
  display: grid;
  grid-template-columns: 250px minmax(0, 760px);
  justify-content: center;
  gap: 70px;
  padding: 80px 5% 110px;
}

.paper-toc {
  position: sticky;
  top: 110px;
  align-self: start;
  padding-top: 10px;
}

.paper-toc p {
  margin: 0 0 13px;
  color: var(--muted);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 1.4px;
  text-transform: uppercase;
}

.paper-toc a {
  display: block;
  padding: 7px 0;
  color: var(--muted);
  font-size: 13px;
}

.paper-toc a:hover { color: var(--blue); }

.paper-article { min-width: 0; }
.paper-article section {
  padding: 0 0 66px;
  scroll-margin-top: 105px;
}

.paper-article section + section {
  padding-top: 66px;
  border-top: 1px solid var(--line);
}

.paper-number {
  display: block;
  margin-bottom: 15px;
  color: var(--blue);
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 1.3px;
}

.paper-article h2 { margin-bottom: 24px; }
.paper-article h3 { margin: 34px 0 11px; font-size: 21px; }
.paper-article p,
.paper-article li { color: #414650; font-size: 17px; line-height: 1.8; }
.paper-article p { margin: 0 0 20px; }
.paper-article ul,
.paper-article ol { margin: 18px 0 24px; padding-left: 24px; }
.paper-article li { margin-bottom: 10px; }
.paper-article strong { color: var(--ink); }

.paper-thesis {
  margin: 34px 0;
  padding: 26px 28px;
  border-left: 5px solid var(--blue);
  background: #eef1ff;
  color: var(--ink) !important;
  font-size: 21px !important;
  font-weight: 600;
  line-height: 1.55 !important;
}

.paper-chain {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: 28px 0;
}

.paper-chain span {
  flex: 1 1 115px;
  padding: 16px 12px;
  border: 1px solid var(--line);
  background: white;
  text-align: center;
  font-size: 14px;
  font-weight: 600;
}

.paper-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
  margin: 26px 0;
}

.paper-card {
  padding: 22px;
  border: 1px solid var(--line);
  background: white;
}

.paper-card h3 { margin: 0 0 9px; font-size: 19px; }
.paper-card p { margin: 0; font-size: 15px; line-height: 1.65; }

.paper-status {
  padding: 20px 22px;
  border: 1px solid #cbd1ff;
  background: #f4f5ff;
}

.paper-status p:last-child { margin-bottom: 0; }

.bibliography li { font-size: 14px; line-height: 1.6; }

.print-button {
  padding: 8px 12px;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: white;
  color: var(--ink);
  cursor: pointer;
  font-size: 13px;
  font-weight: 600;
}

.print-button:hover { border-color: var(--blue); color: var(--blue); }

@media (max-width: 900px) {
  .paper-header .paper-nav { display: none; }
  .paper-shell { grid-template-columns: 1fr; gap: 30px; }
  .paper-toc { position: static; columns: 2; }
  .paper-toc p { column-span: all; }
}

@media (max-width: 600px) {
  .paper-hero { padding: 52px 6% 48px; }
  .paper-hero h1 { margin-top: 30px; letter-spacing: -2px; }
  .paper-hero .paper-deck { margin-left: 0; }
  .paper-shell { padding: 48px 6% 80px; }
  .paper-toc { columns: 1; }
  .paper-grid { grid-template-columns: 1fr; }
  .paper-article p, .paper-article li { font-size: 16px; }
  .print-button { display: none; }
}

@media print {
  .paper-header, .paper-toc, .language-switch, .print-button { display: none !important; }
  .paper-hero { padding: 25mm 18mm 18mm; background: white; color: black; }
  .paper-hero .paper-deck, .paper-hero__meta { color: #444; }
  .paper-shell { display: block; padding: 15mm 18mm; }
  .paper-article section { break-inside: avoid; }
  .paper-card, .paper-chain span { border-color: #aaa; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  * { transition: none !important; }
}