/* ═══════════════════════════════════════════════════════════════
   yuhangwu.com — design system
   Hand-written. Concept: “Signal & Score” — editorial typography
   over warm paper, with an audio-waveform motif.
   ═══════════════════════════════════════════════════════════════ */

/* ── Tokens ─────────────────────────────────────────────────── */
:root {
  --bg:        #FAF8F3;
  --bg-raised: #FFFFFF;
  --ink:       #1C1A16;
  --ink-soft:  #5C574C;
  --line:      #E6E1D5;
  --accent:    #2743D0;
  --accent-ink:#1D33A8;
  --accent-bg: rgba(39, 67, 208, 0.07);
  --chip-bg:   #F0EDE4;
  --code-bg:   #F2EFE8;
  --shadow:    0 1px 2px rgba(28, 26, 22, .04), 0 8px 24px rgba(28, 26, 22, .05);

  --serif: "Fraunces", Georgia, serif;
  --sans:  "Inter", -apple-system, "Segoe UI", sans-serif;
  --mono:  "JetBrains Mono", ui-monospace, "Cascadia Code", monospace;
}

[data-theme="dark"] {
  --bg:        #121110;
  --bg-raised: #1B1917;
  --ink:       #EDE9E1;
  --ink-soft:  #A39D90;
  --line:      #2C2924;
  --accent:    #8FA3FF;
  --accent-ink:#AEBDFF;
  --accent-bg: rgba(143, 163, 255, 0.09);
  --chip-bg:   #232019;
  --code-bg:   #201E1B;
  --shadow:    0 1px 2px rgba(0, 0, 0, .3), 0 8px 24px rgba(0, 0, 0, .25);
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg:        #121110;
    --bg-raised: #1B1917;
    --ink:       #EDE9E1;
    --ink-soft:  #A39D90;
    --line:      #2C2924;
    --accent:    #8FA3FF;
    --accent-ink:#AEBDFF;
    --accent-bg: rgba(143, 163, 255, 0.09);
    --chip-bg:   #232019;
    --code-bg:   #201E1B;
    --shadow:    0 1px 2px rgba(0, 0, 0, .3), 0 8px 24px rgba(0, 0, 0, .25);
  }
}

/* ── Reset & base ───────────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; }
* { margin: 0; }

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  background: var(--bg);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 1.0625rem;
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
  transition: background .3s ease, color .3s ease;
}

img, svg, video { max-width: 100%; display: block; }

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

a { color: var(--accent); text-decoration: none; }
a:hover { color: var(--accent-ink); }

:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 3px;
  border-radius: 2px;
}

.mono { font-family: var(--mono); }

.wrap {
  max-width: 1080px;
  margin-inline: auto;
  padding-inline: clamp(1.25rem, 5vw, 2.75rem);
}

.wrap-narrow {
  max-width: 760px;
  margin-inline: auto;
  padding-inline: clamp(1.25rem, 5vw, 2rem);
}

/* ── Nav ────────────────────────────────────────────────────── */
.nav-bar {
  position: sticky;
  top: 0;
  z-index: 50;
  background: color-mix(in srgb, var(--bg) 82%, transparent);
  -webkit-backdrop-filter: blur(12px);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--line);
}

.nav-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  height: 3.75rem;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: .6rem;
  color: var(--ink);
  font-family: var(--serif);
  font-weight: 600;
  font-size: 1.05rem;
  letter-spacing: -0.01em;
}
.brand:hover { color: var(--accent); }

.mark { width: 20px; height: 20px; color: var(--accent); flex: none; }

.nav-links {
  display: flex;
  align-items: center;
  gap: clamp(.9rem, 2.5vw, 1.75rem);
}

.nav-links a {
  font-family: var(--mono);
  font-size: .76rem;
  font-weight: 500;
  letter-spacing: .14em;
  text-transform: uppercase;
  color: var(--ink-soft);
}
.nav-links a:hover { color: var(--accent); }

.nav-links .lang-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  height: 2rem;
  min-width: 2.4rem;
  padding: 0 .55rem;
  border: 1px solid var(--line);
  border-radius: 999px;
  color: var(--ink-soft);
  font-size: .72rem;
  letter-spacing: .08em;
  transition: color .2s, border-color .2s;
}
.nav-links .lang-btn:hover { color: var(--accent); border-color: var(--accent); }

/* Chinese pages: serif fallback for hanzi, keep Fraunces for latin */
html:lang(zh) {
  --serif: "Fraunces", "Noto Serif SC", "Songti SC", Georgia, serif;
  --sans: "Inter", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
}

#theme-toggle {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 2rem;
  height: 2rem;
  padding: 0;
  border: 1px solid var(--line);
  border-radius: 50%;
  background: transparent;
  color: var(--ink-soft);
  cursor: pointer;
  transition: color .2s, border-color .2s, transform .2s;
}
#theme-toggle:hover { color: var(--accent); border-color: var(--accent); transform: rotate(15deg); }
#theme-toggle svg { width: 15px; height: 15px; }

/* show moon in light mode, sun in dark mode */
.ico-sun  { display: none; }
.ico-moon { display: block; }
[data-theme="dark"] .ico-sun  { display: block; }
[data-theme="dark"] .ico-moon { display: none; }
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) .ico-sun  { display: block; }
  :root:not([data-theme="light"]) .ico-moon { display: none; }
}

/* ── Hero ───────────────────────────────────────────────────── */
.hero {
  padding-block: clamp(4rem, 11vw, 8.5rem) clamp(3rem, 7vw, 5.5rem);
}

.kicker {
  font-family: var(--mono);
  font-size: .78rem;
  font-weight: 500;
  letter-spacing: .22em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 1.5rem;
}
.kicker .zh { letter-spacing: .35em; color: var(--ink-soft); }

.hero h1 {
  font-family: var(--serif);
  font-size: clamp(2.9rem, 8.5vw, 5.6rem);
  font-weight: 600;
  line-height: 1.04;
  letter-spacing: -0.025em;
  margin-bottom: 1.75rem;
}

.hero h1 .aka {
  font-style: italic;
  font-weight: 500;
  color: var(--ink-soft);
}

.hero .lede {
  max-width: 44rem;
  font-size: clamp(1.05rem, 2vw, 1.22rem);
  line-height: 1.72;
  color: var(--ink-soft);
  margin-bottom: 2.25rem;
}
.hero .lede strong { color: var(--ink); font-weight: 600; }

.hero-links {
  display: flex;
  flex-wrap: wrap;
  gap: .7rem;
  margin-bottom: 2.75rem;
}

.pill {
  display: inline-flex;
  align-items: center;
  gap: .5rem;
  padding: .55rem 1.05rem;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: var(--bg-raised);
  color: var(--ink);
  font-family: var(--mono);
  font-size: .8rem;
  font-weight: 500;
  letter-spacing: .04em;
  transition: border-color .2s, color .2s, transform .2s, box-shadow .2s;
}
.pill svg { width: 15px; height: 15px; flex: none; }
.pill:hover {
  border-color: var(--accent);
  color: var(--accent);
  transform: translateY(-2px);
  box-shadow: var(--shadow);
}
.pill--accent {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
}
.pill--accent:hover { color: #fff; filter: brightness(1.1); }

.venues {
  font-family: var(--mono);
  font-size: .78rem;
  letter-spacing: .12em;
  text-transform: uppercase;
  color: var(--ink-soft);
  margin-bottom: 2.5rem;
}
.venues b { color: var(--ink); font-weight: 500; }

/* waveform */
.wave {
  display: flex;
  align-items: center;
  gap: 4px;
  height: 72px;
  overflow: hidden;
  -webkit-mask-image: linear-gradient(to right, transparent, #000 6%, #000 82%, transparent);
  mask-image: linear-gradient(to right, transparent, #000 6%, #000 82%, transparent);
}
.wave span {
  flex: 0 0 3px;
  height: calc(var(--h, .5) * 100%);
  border-radius: 2px;
  background: var(--accent);
  opacity: .85;
  animation: wob 2.4s ease-in-out var(--d, 0ms) infinite alternate;
}
@keyframes wob {
  from { transform: scaleY(1); }
  to   { transform: scaleY(.3); }
}
@media (prefers-reduced-motion: reduce) {
  .wave span { animation: none; }
  html { scroll-behavior: auto; }
}

/* ── Sections ───────────────────────────────────────────────── */
.section { padding-block: clamp(3rem, 7vw, 5.5rem); }
.section + .section { border-top: 1px solid var(--line); }
.section:target { scroll-margin-top: 4.5rem; }
[id] { scroll-margin-top: 4.5rem; }

.sec-head {
  display: flex;
  align-items: baseline;
  gap: 1rem;
  margin-bottom: clamp(1.75rem, 4vw, 2.75rem);
}

.sec-num {
  font-family: var(--mono);
  font-size: .8rem;
  font-weight: 500;
  color: var(--accent);
  letter-spacing: .1em;
}

.sec-head h2 {
  font-family: var(--serif);
  font-size: clamp(1.7rem, 3.5vw, 2.3rem);
  font-weight: 600;
  letter-spacing: -0.015em;
  line-height: 1.15;
}

.sec-head::after {
  content: "";
  flex: 1;
  height: 1px;
  background: var(--line);
  transform: translateY(-4px);
}

/* about */
.about-grid {
  display: grid;
  grid-template-columns: minmax(0, 1.6fr) minmax(0, 1fr);
  gap: clamp(2rem, 5vw, 4rem);
}

.about-text p { margin-bottom: 1.15rem; color: var(--ink-soft); }
.about-text p:last-child { margin-bottom: 0; }
.about-text strong, .about-text a { font-weight: 600; }
.about-text strong { color: var(--ink); }

.about-side h3 {
  font-family: var(--mono);
  font-size: .76rem;
  font-weight: 500;
  letter-spacing: .18em;
  text-transform: uppercase;
  color: var(--ink-soft);
  margin-bottom: 1rem;
}

.photo-card {
  margin: 0 0 1.75rem;
  padding: .6rem .6rem 1rem;
  background: var(--bg-raised);
  border: 1px solid var(--line);
  border-radius: 12px;
  box-shadow: var(--shadow);
  transform: rotate(-1.2deg);
  transition: transform .3s ease;
  max-width: 340px;
}
.photo-card:hover { transform: rotate(0deg) scale(1.01); }
.photo-card img { border-radius: 7px; width: 100%; }

.photo-band {
  border-block: 1px solid var(--line);
  line-height: 0;
}
.photo-band img {
  width: 100%;
  height: clamp(180px, 30vw, 320px);
  object-fit: cover;
  object-position: center 60%;
}
[data-theme="dark"] .photo-band img { filter: brightness(.82); }
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) .photo-band img { filter: brightness(.82); }
}

.chips { display: flex; flex-wrap: wrap; gap: .5rem; }

.chip {
  padding: .32rem .8rem;
  border-radius: 999px;
  background: var(--chip-bg);
  border: 1px solid var(--line);
  font-family: var(--mono);
  font-size: .76rem;
  font-weight: 500;
  color: var(--ink);
  letter-spacing: .02em;
}

.chip--hi {
  background: var(--accent-bg);
  border-color: color-mix(in srgb, var(--accent) 35%, transparent);
  color: var(--accent-ink);
}

/* publications */
.pub-list { display: grid; gap: 1.1rem; }

.pub {
  position: relative;
  padding: 1.5rem 1.6rem 1.4rem;
  background: var(--bg-raised);
  border: 1px solid var(--line);
  border-radius: 14px;
  transition: border-color .2s, box-shadow .25s, transform .25s;
}
.pub:hover {
  border-color: color-mix(in srgb, var(--accent) 45%, var(--line));
  box-shadow: var(--shadow);
  transform: translateY(-2px);
}

.pub-venue {
  display: inline-flex;
  align-items: center;
  gap: .45rem;
  font-family: var(--mono);
  font-size: .72rem;
  font-weight: 500;
  letter-spacing: .14em;
  text-transform: uppercase;
  color: var(--accent);
  background: var(--accent-bg);
  padding: .28rem .7rem;
  border-radius: 999px;
  margin-bottom: .85rem;
}

.pub h3 {
  font-family: var(--serif);
  font-size: clamp(1.15rem, 2.2vw, 1.4rem);
  font-weight: 600;
  line-height: 1.3;
  letter-spacing: -0.01em;
  margin-bottom: .5rem;
}
.pub h3 a { color: var(--ink); }
.pub h3 a:hover { color: var(--accent); }

.pub-authors {
  font-size: .92rem;
  color: var(--ink-soft);
  line-height: 1.6;
  margin-bottom: .75rem;
}
.pub-authors b { color: var(--ink); font-weight: 600; }

.pub-links { display: flex; gap: 1.1rem; }
.pub-links a {
  font-family: var(--mono);
  font-size: .78rem;
  font-weight: 500;
  letter-spacing: .06em;
}
.pub-links a::after { content: " ↗"; }

/* experience timeline */
.timeline { position: relative; display: grid; gap: 0; }
.timeline::before {
  content: "";
  position: absolute;
  left: 5px;
  top: 8px;
  bottom: 8px;
  width: 1px;
  background: var(--line);
}

.t-item {
  position: relative;
  padding: 0 0 2.1rem 2.1rem;
}
.t-item:last-child { padding-bottom: 0; }

.t-item::before {
  content: "";
  position: absolute;
  left: 0;
  top: .48rem;
  width: 11px;
  height: 11px;
  border-radius: 50%;
  background: var(--bg);
  border: 2.5px solid var(--accent);
}

.t-meta {
  font-family: var(--mono);
  font-size: .76rem;
  font-weight: 500;
  letter-spacing: .1em;
  text-transform: uppercase;
  color: var(--ink-soft);
  margin-bottom: .3rem;
}
.t-meta b { color: var(--accent); font-weight: 500; }

.t-item h3 {
  font-family: var(--sans);
  font-size: 1.08rem;
  font-weight: 600;
  line-height: 1.4;
  margin-bottom: .35rem;
}
.t-item h3 span { font-weight: 400; color: var(--ink-soft); }

.t-item p { font-size: .95rem; color: var(--ink-soft); max-width: 46rem; }

/* education + skills two-up */
.duo {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: clamp(2rem, 5vw, 4rem);
}

.edu { display: grid; gap: 1.6rem; }
.edu-item h3 { font-size: 1.05rem; font-weight: 600; line-height: 1.45; }
.edu-item .t-meta { margin-bottom: .25rem; }
.edu-item p { font-size: .93rem; color: var(--ink-soft); }

.skills { display: grid; gap: 1.4rem; }
.skill-group h3 {
  font-family: var(--mono);
  font-size: .74rem;
  font-weight: 500;
  letter-spacing: .18em;
  text-transform: uppercase;
  color: var(--ink-soft);
  margin-bottom: .6rem;
}

/* writing list */
.post-list { display: grid; gap: 0; }

.post-row {
  display: flex;
  align-items: baseline;
  gap: 1.25rem;
  padding: 1.05rem 0;
  border-bottom: 1px solid var(--line);
  color: var(--ink);
}
.post-row:first-child { border-top: 1px solid var(--line); }

.post-row time {
  flex: none;
  width: 6.2rem;
  font-family: var(--mono);
  font-size: .78rem;
  color: var(--ink-soft);
  letter-spacing: .04em;
}

.post-row .post-name {
  font-family: var(--serif);
  font-size: 1.12rem;
  font-weight: 600;
  letter-spacing: -0.01em;
  line-height: 1.4;
  transition: color .15s;
}
.post-row:hover .post-name { color: var(--accent); }

.post-row .arrow {
  margin-left: auto;
  flex: none;
  color: var(--ink-soft);
  transition: transform .2s, color .2s;
}
.post-row:hover .arrow { transform: translate(3px, -3px); color: var(--accent); }

.more-link {
  display: inline-block;
  margin-top: 1.5rem;
  font-family: var(--mono);
  font-size: .8rem;
  font-weight: 500;
  letter-spacing: .1em;
  text-transform: uppercase;
}

/* year headers on /blog/ */
.year-head {
  font-family: var(--serif);
  font-size: 1.5rem;
  font-weight: 600;
  color: var(--ink-soft);
  margin: 2.5rem 0 .5rem;
}
.year-head:first-of-type { margin-top: 0; }

.page-head { padding-block: clamp(3rem, 8vw, 5rem) 1rem; }
.page-head h1 {
  font-family: var(--serif);
  font-size: clamp(2.2rem, 6vw, 3.4rem);
  font-weight: 600;
  letter-spacing: -0.02em;
  margin-bottom: .75rem;
}
.page-head p { color: var(--ink-soft); max-width: 40rem; }

/* ── Post page ──────────────────────────────────────────────── */
.post { padding-block: clamp(3rem, 8vw, 5rem); }

.post-head { margin-bottom: 2.75rem; }

.post-meta {
  font-size: .8rem;
  color: var(--ink-soft);
  letter-spacing: .05em;
  margin-bottom: 1rem;
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: .55rem;
}
.post-meta .dot { color: var(--line); }
.post-meta .tag {
  background: var(--chip-bg);
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: .12rem .6rem;
  font-size: .72rem;
}

.post-title {
  font-family: var(--serif);
  font-size: clamp(1.9rem, 5.5vw, 3rem);
  font-weight: 600;
  line-height: 1.15;
  letter-spacing: -0.02em;
  margin-bottom: .9rem;
}

.post-subtitle {
  font-size: 1.15rem;
  color: var(--ink-soft);
  font-style: italic;
  font-family: var(--serif);
  font-weight: 500;
}

.post-body { font-size: 1.05rem; }
.post-body > * + * { margin-top: 1.2rem; }

.post-body h2, .post-body h3, .post-body h4 {
  font-family: var(--serif);
  font-weight: 600;
  letter-spacing: -0.01em;
  line-height: 1.3;
  margin-top: 2.4rem;
}
.post-body h2 { font-size: 1.65rem; }
.post-body h3 { font-size: 1.32rem; }
.post-body h4 { font-size: 1.12rem; }

.post-body h2::before {
  content: "§ ";
  color: var(--accent);
  font-weight: 500;
}

.post-body a { text-decoration: underline; text-decoration-color: color-mix(in srgb, var(--accent) 40%, transparent); text-underline-offset: 3px; }
.post-body a:hover { text-decoration-color: var(--accent); }

.post-body blockquote {
  border-left: 3px solid var(--accent);
  padding: .35rem 0 .35rem 1.25rem;
  color: var(--ink-soft);
  font-style: italic;
}

.post-body ul, .post-body ol { padding-left: 1.4rem; }
.post-body li { margin-top: .45rem; }
.post-body li::marker { color: var(--accent); }

.post-body img {
  border-radius: 10px;
  border: 1px solid var(--line);
  margin-inline: auto;
}

.post-body hr { border: none; border-top: 1px solid var(--line); margin-block: 2.5rem; }

.post-body code {
  font-family: var(--mono);
  font-size: .86em;
  background: var(--code-bg);
  border: 1px solid var(--line);
  border-radius: 5px;
  padding: .12em .4em;
}

.post-body pre {
  background: var(--code-bg);
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 1.1rem 1.3rem;
  overflow-x: auto;
  line-height: 1.6;
}
.post-body pre code { background: none; border: none; padding: 0; font-size: .84rem; }

.post-body table {
  width: 100%;
  border-collapse: collapse;
  font-size: .92rem;
  display: block;
  overflow-x: auto;
}
.post-body th, .post-body td {
  border: 1px solid var(--line);
  padding: .55rem .9rem;
  text-align: left;
}
.post-body th { background: var(--chip-bg); font-weight: 600; }

/* MathJax display blocks can overflow on phones */
.post-body .MathJax_Display, .post-body .MJXc-display {
  overflow-x: auto;
  overflow-y: hidden;
  max-width: 100%;
}

.post-foot {
  margin-top: 3.5rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--line);
}
.back-link { font-size: .8rem; letter-spacing: .08em; text-transform: uppercase; }

/* ── 404 ────────────────────────────────────────────────────── */
.err {
  min-height: 55vh;
  display: grid;
  place-content: center;
  text-align: center;
  gap: 1rem;
  padding-block: 4rem;
}
.err-avatar {
  width: 88px;
  height: 88px;
  border-radius: 50%;
  border: 2px solid var(--line);
  margin-inline: auto;
  filter: grayscale(1);
}
.err .code {
  font-family: var(--mono);
  font-size: clamp(4rem, 15vw, 7rem);
  font-weight: 500;
  color: var(--accent);
  line-height: 1;
}
.err p { color: var(--ink-soft); }

/* ── Footer ─────────────────────────────────────────────────── */
.site-footer {
  border-top: 1px solid var(--line);
  padding-block: 2.25rem;
  margin-top: clamp(3rem, 8vw, 5rem);
}

.footer-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1.25rem;
  flex-wrap: wrap;
}

.footer-left { display: flex; align-items: center; gap: .75rem; }
.footer-left .mark { width: 16px; height: 16px; }
.footer-left p { font-size: .85rem; color: var(--ink-soft); }
.footer-left .coords {
  font-family: var(--mono);
  font-size: .72rem;
  letter-spacing: .08em;
  margin-left: .5rem;
  opacity: .7;
}

.footer-links { display: flex; gap: 1.4rem; }
.footer-links a {
  font-family: var(--mono);
  font-size: .76rem;
  font-weight: 500;
  letter-spacing: .12em;
  text-transform: uppercase;
  color: var(--ink-soft);
}
.footer-links a:hover { color: var(--accent); }

/* ── Responsive ─────────────────────────────────────────────── */
@media (max-width: 860px) {
  .about-grid { grid-template-columns: 1fr; }
  .duo { grid-template-columns: 1fr; }
}

@media (max-width: 640px) {
  body { font-size: 1rem; }
  .hide-sm { display: none; }
  .brand-name { display: none; }
  .nav-links { gap: 1.1rem; }
  .nav-links a { font-size: .72rem; }
  .pub { padding: 1.2rem 1.2rem 1.1rem; }
  .post-row { gap: .85rem; }
  .post-row time { width: 5.4rem; font-size: .72rem; }
  .post-row .post-name { font-size: 1.02rem; }
  .footer-inner { flex-direction: column; align-items: flex-start; }
  .wave { height: 56px; }
}