/* ————————————————————————————————————————————————
   Bitcoin Whitepaper · Bilingual Edition
   “创世文献” — warm paper & ink, editorial typesetting
   ———————————————————————————————————————————————— */

:root {
  --serif-en: "Iowan Old Style", "Palatino Linotype", Palatino, "Book Antiqua", Charter, Georgia, "Times New Roman", serif;
  --serif-zh: "Iowan Old Style", Palatino, Georgia, "Songti SC", "Noto Serif SC", "Source Han Serif SC", STSong, SimSun, serif;
  --mono: ui-monospace, "SF Mono", Menlo, "JetBrains Mono", Consolas, "Liberation Mono", monospace;

  --bg: #f6f1e7;
  --bg-deep: #efe8d9;
  --paper: #fdfaf3;
  --ink: #211c15;
  --ink-soft: #6b6152;
  --ink-faint: #9b9080;
  --rule: rgba(33, 28, 21, 0.16);
  --rule-soft: rgba(33, 28, 21, 0.08);
  --accent: #d97706;
  --accent-strong: #b45309;
  --accent-glow: rgba(247, 147, 26, 0.14);
  --code-bg: #1f1a12;
  --code-ink: #e9dfc9;
  --shadow: 0 1px 2px rgba(33, 28, 21, 0.05), 0 12px 40px -18px rgba(33, 28, 21, 0.25);
}

[data-theme="dark"] {
  --bg: #14110b;
  --bg-deep: #0e0c07;
  --paper: #1c1811;
  --ink: #ede4d0;
  --ink-soft: #a99c84;
  --ink-faint: #7a6f5c;
  --rule: rgba(237, 228, 208, 0.16);
  --rule-soft: rgba(237, 228, 208, 0.07);
  --accent: #f7931a;
  --accent-strong: #fbb03b;
  --accent-glow: rgba(247, 147, 26, 0.09);
  --code-bg: #0d0b06;
  --code-ink: #dfd4bb;
  --shadow: 0 1px 2px rgba(0, 0, 0, 0.4), 0 16px 48px -20px rgba(0, 0, 0, 0.7);
}

* { margin: 0; padding: 0; box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  background: var(--bg);
  color: var(--ink);
  font-family: var(--serif-en);
  font-size: 17px;
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
  transition: background 0.35s ease, color 0.35s ease;
}

/* paper grain */
body::before {
  content: "";
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: 1000;
  opacity: 0.35;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='140' height='140'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='2'/%3E%3CfeColorMatrix values='0 0 0 0 0.5 0 0 0 0 0.45 0 0 0 0 0.35 0 0 0 0.05 0'/%3E%3C/filter%3E%3Crect width='140' height='140' filter='url(%23n)'/%3E%3C/svg%3E");
}

::selection { background: var(--accent); color: #fff8ec; }

a { color: inherit; }

/* ————— progress bar ————— */
#progress {
  position: fixed;
  top: 0; left: 0;
  height: 3px;
  width: 0;
  background: linear-gradient(90deg, #b45309, #f7931a);
  z-index: 90;
  transition: width 0.1s linear;
}

/* ————— top bar ————— */
.topbar {
  position: fixed;
  top: 0; left: 0; right: 0;
  z-index: 80;
  display: flex;
  align-items: center;
  gap: 1rem;
  padding: 0.7rem 1.4rem;
  border-bottom: 1px solid transparent;
  transition: background 0.3s ease, border-color 0.3s ease, backdrop-filter 0.3s ease;
}
.topbar.scrolled {
  background: color-mix(in srgb, var(--bg) 82%, transparent);
  backdrop-filter: blur(14px) saturate(1.4);
  -webkit-backdrop-filter: blur(14px) saturate(1.4);
  border-bottom-color: var(--rule-soft);
}
.topbar .brand {
  display: flex;
  align-items: baseline;
  gap: 0.6rem;
  text-decoration: none;
  opacity: 0;
  transform: translateY(-4px);
  transition: opacity 0.3s ease, transform 0.3s ease;
}
.topbar.scrolled .brand { opacity: 1; transform: none; }
.brand .btc-mark {
  font-family: var(--serif-en);
  font-weight: 700;
  font-size: 1.15rem;
  color: var(--accent);
}
.brand .brand-title {
  font-size: 0.82rem;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--ink-soft);
  font-family: var(--mono);
}
.topbar .spacer { flex: 1; }
.lang-tag {
  font-family: var(--mono);
  font-size: 0.7rem;
  letter-spacing: 0.22em;
  color: var(--ink-faint);
  text-transform: uppercase;
}
.lang-tag b { color: var(--accent); font-weight: 600; }

#theme-toggle,
.icon-btn {
  appearance: none;
  border: 1px solid var(--rule);
  background: var(--paper);
  color: var(--ink);
  width: 34px; height: 34px;
  border-radius: 50%;
  font-size: 0.95rem;
  cursor: pointer;
  display: grid;
  place-items: center;
  transition: transform 0.25s ease, border-color 0.25s ease, color 0.25s ease;
  line-height: 1;
  text-decoration: none;
}
#theme-toggle:hover { transform: rotate(30deg); border-color: var(--accent); }
.icon-btn:hover { border-color: var(--accent); color: var(--accent); transform: translateY(-2px); }

/* ————— hero ————— */
.hero {
  position: relative;
  min-height: 92vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: 7rem 1.5rem 5rem;
  overflow: hidden;
  isolation: isolate;
}
.hero::before {
  content: "₿";
  position: absolute;
  z-index: -1;
  font-size: min(120vh, 88vw);
  line-height: 1;
  font-family: var(--serif-en);
  font-weight: 700;
  color: transparent;
  -webkit-text-stroke: 1.5px color-mix(in srgb, var(--accent) 26%, transparent);
  top: 50%; left: 50%;
  transform: translate(-50%, -52%);
  user-select: none;
  animation: heroGlyph 2.4s cubic-bezier(0.22, 1, 0.36, 1) both;
}
.hero::after {
  content: "";
  position: absolute;
  inset: 0;
  z-index: -1;
  background:
    radial-gradient(ellipse 60% 45% at 50% 42%, var(--accent-glow), transparent 70%),
    radial-gradient(ellipse 90% 60% at 50% 110%, var(--accent-glow), transparent 60%);
}
@keyframes heroGlyph {
  from { opacity: 0; transform: translate(-50%, -48%) scale(0.96); }
  to   { opacity: 1; transform: translate(-50%, -52%) scale(1); }
}
.hero > * { animation: riseIn 0.9s cubic-bezier(0.22, 1, 0.36, 1) both; }
.hero > *:nth-child(1) { animation-delay: 0.1s; }
.hero > *:nth-child(2) { animation-delay: 0.22s; }
.hero > *:nth-child(3) { animation-delay: 0.34s; }
.hero > *:nth-child(4) { animation-delay: 0.46s; }
.hero > *:nth-child(5) { animation-delay: 0.58s; }
.hero > *:nth-child(6) { animation-delay: 0.7s; }
@keyframes riseIn {
  from { opacity: 0; transform: translateY(22px); }
  to   { opacity: 1; transform: none; }
}

.hero .kicker {
  font-family: var(--mono);
  font-size: 0.72rem;
  letter-spacing: 0.34em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 2.2rem;
}
.hero h1 {
  font-size: clamp(2rem, 5.2vw, 3.9rem);
  line-height: 1.12;
  font-weight: 600;
  letter-spacing: -0.015em;
  max-width: 21ch;
}
.hero .h1-zh {
  font-family: var(--serif-zh);
  font-size: clamp(1.25rem, 3vw, 2.1rem);
  font-weight: 500;
  color: var(--ink-soft);
  margin-top: 1.1rem;
  letter-spacing: 0.06em;
}
.hero .meta {
  margin-top: 3rem;
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 0.4rem 2.2rem;
  font-family: var(--mono);
  font-size: 0.78rem;
  color: var(--ink-soft);
}
.hero .meta span::before {
  content: "· ";
  color: var(--accent);
}
.hero .genesis {
  margin-top: 2.6rem;
  font-family: var(--mono);
  font-size: 0.66rem;
  letter-spacing: 0.06em;
  color: var(--ink-faint);
  max-width: 60ch;
  word-break: break-all;
}
.hero .genesis em {
  display: block;
  font-style: normal;
  letter-spacing: 0.28em;
  text-transform: uppercase;
  font-size: 0.62rem;
  margin-bottom: 0.5rem;
  color: var(--accent);
}
.hero .scroll-hint {
  position: absolute;
  bottom: 2rem;
  left: 50%;
  transform: translateX(-50%);
  font-size: 1.1rem;
  color: var(--ink-faint);
  animation: bob 2.2s ease-in-out infinite;
}
@keyframes bob {
  0%, 100% { transform: translate(-50%, 0); opacity: 0.5; }
  50% { transform: translate(-50%, 8px); opacity: 1; }
}

/* ————— layout ————— */
.wrap {
  max-width: 1240px;
  margin: 0 auto;
  padding: 0 2.2rem 6rem;
}

/* ————— TOC rail ————— */
.toc {
  position: fixed;
  left: max(0.8rem, calc(50vw - 620px - 200px));
  top: 50%;
  transform: translateY(-50%);
  width: 168px;
  z-index: 60;
  display: none;
}
@media (min-width: 1660px) { .toc { display: block; } }
.toc ol {
  list-style: none;
  border-left: 1px solid var(--rule-soft);
}
.toc a {
  display: block;
  padding: 0.22rem 0 0.22rem 0.9rem;
  font-family: var(--serif-zh);
  font-size: 0.76rem;
  color: var(--ink-faint);
  text-decoration: none;
  border-left: 2px solid transparent;
  margin-left: -1.5px;
  transition: color 0.2s ease, border-color 0.2s ease;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.toc a:hover { color: var(--ink); }
.toc li.active a {
  color: var(--accent);
  border-left-color: var(--accent);
}
.toc .toc-num {
  font-family: var(--mono);
  font-size: 0.62rem;
  margin-right: 0.45em;
  opacity: 0.7;
}

/* ————— sections ————— */
.section { padding-top: 5.5rem; }

.sec-head {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0 5rem;
  align-items: baseline;
  position: relative;
  padding-bottom: 1.4rem;
  margin-bottom: 2.6rem;
  border-bottom: 1px solid var(--rule);
}
.sec-head::after {
  content: "";
  position: absolute;
  bottom: -1px;
  left: 0;
  width: 64px;
  height: 3px;
  background: var(--accent);
}
.sec-head .num {
  position: absolute;
  top: -2.9rem;
  left: 0;
  font-family: var(--mono);
  font-size: 0.72rem;
  letter-spacing: 0.3em;
  color: var(--accent);
}
.sec-head h2 {
  font-size: clamp(1.45rem, 2.6vw, 2rem);
  font-weight: 600;
  letter-spacing: -0.01em;
  line-height: 1.25;
}
.sec-head h2.zh {
  font-family: var(--serif-zh);
  font-weight: 500;
  letter-spacing: 0.04em;
}

/* ————— bilingual pairs ————— */
.pair {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0 5rem;
  position: relative;
  padding: 0.85rem 0;
}
.pair::before {
  content: "";
  position: absolute;
  top: 0.9rem; bottom: 0.9rem;
  left: 50%;
  width: 1px;
  background: var(--rule-soft);
  transition: background 0.25s ease;
}
.pair:hover::before { background: color-mix(in srgb, var(--accent) 55%, transparent); }

.pair .en {
  color: var(--ink);
  text-align: left;
  hyphens: auto;
}
.pair .zh {
  font-family: var(--serif-zh);
  font-size: 0.98em;
  line-height: 1.95;
  text-align: justify;
  letter-spacing: 0.01em;
}
.pair .lang-chip { display: none; }

.cite {
  color: var(--accent-strong);
  text-decoration: none;
  font-size: 0.82em;
  vertical-align: super;
  line-height: 0;
  font-family: var(--mono);
}
.cite:hover { text-decoration: underline; }

/* ordered list inside pair (network steps) */
.pair ol {
  padding-left: 1.4em;
  display: flex;
  flex-direction: column;
  gap: 0.45em;
}
.pair ol li::marker { color: var(--accent); font-family: var(--mono); font-size: 0.9em; }

/* ————— figures ————— */
.figure-pair {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0 5rem;
  position: relative;
  margin: 2rem 0 2.4rem;
}
.figure-pair::before {
  content: "";
  position: absolute;
  top: 0; bottom: 0;
  left: 50%;
  width: 1px;
  background: var(--rule-soft);
}
.figure-pair figure {
  background: #fdfcf8;
  border: 1px solid var(--rule);
  border-radius: 10px;
  padding: 1.3rem 1.4rem;
  box-shadow: var(--shadow);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 0.9rem;
  transition: transform 0.3s ease, box-shadow 0.3s ease;
}
.figure-pair figure:hover { transform: translateY(-3px); }
.figure-pair img {
  max-width: 100%;
  height: auto;
  display: block;
}
.figure-pair figcaption {
  font-family: var(--mono);
  font-size: 0.68rem;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: #8a7d66;
}
[data-theme="dark"] .figure-pair figure {
  background: #f5f1e6;
  border-color: rgba(237, 228, 208, 0.25);
}

/* ————— full-bleed neutral blocks (math / code / data) ————— */
.neutral {
  margin: 2.2rem 0;
  position: relative;
}
.neutral .neutral-tag {
  position: absolute;
  top: -0.72rem;
  left: 50%;
  transform: translateX(-50%);
  background: var(--bg);
  padding: 0 0.9rem;
  font-family: var(--mono);
  font-size: 0.62rem;
  letter-spacing: 0.3em;
  text-transform: uppercase;
  color: var(--ink-faint);
  white-space: nowrap;
}

.math-block {
  border: 1px solid var(--rule);
  border-radius: 10px;
  background: var(--paper);
  padding: 2rem 1.5rem;
  display: flex;
  justify-content: center;
  align-items: center;
  overflow-x: auto;
  box-shadow: var(--shadow);
}
.math {
  font-family: var(--serif-en);
  font-size: 1.18rem;
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  white-space: nowrap;
}
.math i { font-style: italic; padding: 0 0.05em; }
.math sub, .math sup { font-size: 0.62em; }
.frac {
  display: inline-flex;
  flex-direction: column;
  align-items: center;
  vertical-align: middle;
  line-height: 1.15;
  margin: 0 0.15em;
}
.frac > .top { padding: 0 0.3em 0.12em; border-bottom: 1.2px solid currentColor; }
.frac > .bot { padding: 0.12em 0.3em 0; }
.brace {
  font-size: 3.4em;
  font-weight: 200;
  line-height: 0.9;
  transform: scaleY(1.1);
  color: var(--ink-soft);
}
.cases {
  display: inline-flex;
  flex-direction: column;
  gap: 0.5em;
  text-align: left;
}
.cases .case-row {
  display: grid;
  grid-template-columns: auto auto;
  gap: 0 1.6em;
  align-items: center;
}
.bigop {
  display: inline-flex;
  flex-direction: column;
  align-items: center;
  line-height: 1;
  margin: 0 0.2em;
}
.bigop .op { font-size: 1.9em; line-height: 0.95; }
.bigop .lim { font-size: 0.58em; color: var(--ink-soft); }

.code-block {
  background: var(--code-bg);
  color: var(--code-ink);
  border-radius: 10px;
  padding: 1.6rem 1.9rem;
  overflow-x: auto;
  box-shadow: var(--shadow);
  border: 1px solid rgba(247, 147, 26, 0.15);
}
.code-block pre {
  font-family: var(--mono);
  font-size: 0.82rem;
  line-height: 1.65;
}
.code-block .kw { color: #f7931a; }
.code-block .cm { color: #8a7d63; }

.neutral > .code-block {
  max-width: 720px;
  margin: 0 auto;
}

.data-cols {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 1.2rem;
  max-width: 860px;
  margin: 0 auto;
}
.data-cols .code-block { display: flex; justify-content: center; }

/* ————— references ————— */
.refs {
  margin-top: 2rem;
  counter-reset: ref;
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.9rem;
  max-width: 62rem;
}
.refs li {
  counter-increment: ref;
  position: relative;
  padding-left: 3rem;
  font-size: 0.92rem;
  color: var(--ink-soft);
  line-height: 1.7;
}
.refs li::before {
  content: "[" counter(ref) "]";
  position: absolute;
  left: 0;
  font-family: var(--mono);
  font-size: 0.78rem;
  color: var(--accent);
  top: 0.2em;
}
.refs i { font-style: italic; }
.refs a { color: var(--accent-strong); text-decoration: none; word-break: break-all; }
.refs a:hover { text-decoration: underline; }

/* ————— footer ————— */
footer {
  border-top: 1px solid var(--rule);
  margin-top: 6rem;
  padding: 3.5rem 2rem 4.5rem;
  text-align: center;
}
footer .times {
  font-family: var(--serif-en);
  font-style: italic;
  font-size: 1.02rem;
  color: var(--ink-soft);
  max-width: 52ch;
  margin: 0 auto;
}
footer .times-zh {
  font-family: var(--serif-zh);
  font-style: normal;
  font-size: 0.86rem;
  color: var(--ink-faint);
  margin-top: 0.7rem;
}
footer .colophon {
  margin-top: 2.4rem;
  font-family: var(--mono);
  font-size: 0.68rem;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--ink-faint);
}
footer .colophon b { color: var(--accent); font-weight: 600; font-family: var(--serif-en); }
footer .colophon-link {
  margin-top: 0.9rem;
  font-family: var(--serif-zh);
  font-size: 0.8rem;
  color: var(--ink-faint);
}
footer .colophon-link a {
  color: var(--accent-strong);
  text-decoration: none;
  font-family: var(--mono);
  font-size: 0.76rem;
}
footer .colophon-link a:hover { text-decoration: underline; }

/* ————— mobile language switch ————— */
.lang-switch {
  position: fixed;
  bottom: 1.2rem;
  left: 50%;
  transform: translateX(-50%);
  z-index: 70;
  display: none;
  gap: 0;
  background: color-mix(in srgb, var(--paper) 88%, transparent);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border: 1px solid var(--rule);
  border-radius: 999px;
  padding: 0.25rem;
  box-shadow: var(--shadow);
}
.lang-switch button {
  appearance: none;
  border: 0;
  background: transparent;
  color: var(--ink-soft);
  font-family: var(--serif-zh);
  font-size: 0.8rem;
  padding: 0.42rem 1.05rem;
  border-radius: 999px;
  cursor: pointer;
  transition: background 0.2s ease, color 0.2s ease;
}
.lang-switch button.active {
  background: var(--accent);
  color: #fff8ec;
}

/* ————— responsive ————— */
@media (max-width: 960px) {
  body { font-size: 16px; }
  .wrap { padding: 0 1.3rem 7rem; }
  .lang-switch { display: inline-flex; }
  .lang-tag { display: none; }
  .brand .brand-title { white-space: nowrap; max-width: 58vw; overflow: hidden; text-overflow: ellipsis; }

  .sec-head,
  .pair,
  .figure-pair {
    grid-template-columns: 1fr;
    gap: 1.1rem;
  }
  .pair::before, .figure-pair::before { display: none; }
  .pair { padding: 0.6rem 0; }
  .pair .zh, .sec-head h2.zh { border-top: 1px dashed var(--rule-soft); padding-top: 1rem; }
  .sec-head h2.zh { margin-top: 0.2rem; }

  /* single-language modes */
  body[data-lang="en"] .zh, body[data-lang="en"] h2.zh, body[data-lang="en"] .fig-zh { display: none; }
  body[data-lang="zh"] .en, body[data-lang="zh"] h2.en, body[data-lang="zh"] .fig-en { display: none; }
  body[data-lang="en"] .pair .en, body[data-lang="zh"] .pair .zh { border-top: 0; padding-top: 0; }
  body[data-lang="zh"] .pair .zh { border-top: 0; padding-top: 0; }

  .hero { min-height: 86vh; }
  .hero .meta { gap: 0.3rem 1.3rem; font-size: 0.7rem; }
  .toc { display: none !important; }
}

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