/* ============================================================
   about.yuxiang.io — Yuxiang Gao, roboticist · founder of COCO Matrix
   A minimal, prose-first personal page.
   Palette: cyan-tinted ink + COCO cyan + a dusk violet from the portrait.
   Type: Sora (display) / IBM Plex Sans + IBM Plex Sans SC (prose)
         / IBM Plex Mono (dates, labels, the "//" motif)
   Mono type scale: 0.8rem nav · 0.75rem captions · 0.72rem micro-labels
   ============================================================ */

:root {
  --bg: #060f16;
  --text: #e8f1f4;
  --muted: #9ab0ba;
  --faint: #64808c;
  --line: rgba(232, 241, 244, 0.1);
  --cyan: #12d2f2;
  --cyan-soft: rgba(18, 210, 242, 0.09);
  --cyan-a25: rgba(18, 210, 242, 0.25);
  --cyan-a45: rgba(18, 210, 242, 0.45);
  --cyan-a55: rgba(18, 210, 242, 0.55);
  --dusk: #c88bf0;
  --dusk-a55: rgba(200, 139, 240, 0.55);
  --dusk-glow: rgba(200, 139, 240, 0.13);
  --radius-card: 16px;
  /* One superfamily across both languages: IBM Plex Sans + its SC
     sibling share the same skeleton, so 中/EN switching keeps the voice. */
  --font-display: "Sora", "IBM Plex Sans SC", "PingFang SC", sans-serif;
  --font-body: "IBM Plex Sans", "IBM Plex Sans SC", "PingFang SC", "Microsoft YaHei", sans-serif;
  --font-mono: "IBM Plex Mono", "IBM Plex Sans SC", ui-monospace, monospace;
}

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

body {
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-body);
  font-size: 1.0625rem;
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
  overflow-x: hidden;
}

::selection {
  background: var(--dusk);
  color: var(--bg);
}

a {
  color: var(--cyan);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
  text-underline-offset: 3px;
}

img {
  max-width: 100%;
  height: auto;
  display: block;
}

:focus-visible {
  outline: 2px solid var(--cyan);
  outline-offset: 3px;
  border-radius: 4px;
}

.container {
  max-width: 44rem;
  margin-inline: auto;
  padding-inline: clamp(1.25rem, 5vw, 2rem);
}

/* ---------- header ---------- */

.top {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.5rem 1rem;
  padding-top: 2rem;
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  color: var(--text);
  font-family: var(--font-display);
  font-weight: 600;
  font-size: 0.95rem;
  white-space: nowrap;
}

.brand:hover {
  text-decoration: none;
  color: var(--cyan);
}

/* the robot mark's colors live here, not in the SVG markup */
.coco-mark .body,
.coco-mark .pupils {
  fill: var(--cyan);
}

.coco-mark .face {
  fill: #ffffff;
}

.brand img {
  width: 22px;
  height: 22px;
}

.brand .zh {
  color: var(--faint);
  font-family: var(--font-body);
  font-weight: 400;
}

.top-links {
  margin-left: auto;
  display: flex;
  gap: 1.25rem;
  font-family: var(--font-mono);
  font-size: 0.8rem;
}

.top-links a {
  color: var(--muted);
}

.top-links a:hover {
  color: var(--cyan);
  text-decoration: none;
}

/* ---------- language switch ---------- */
/* One language visible at a time; the header button flips
   html[data-lang] and the rules below do the rest. */

[data-lang="en"] .zh-only {
  display: none !important;
}

[data-lang="zh"] .en-only {
  display: none !important;
}

.lang-toggle {
  background: none;
  border: 1px solid var(--line);
  border-radius: 999px;
  color: var(--muted);
  font-family: var(--font-mono);
  font-size: 0.72rem;
  letter-spacing: 0.05em;
  padding: 0.18rem 0.75rem;
  cursor: pointer;
}

.lang-toggle:hover {
  color: var(--cyan);
  border-color: var(--cyan-a45);
}

[data-lang="zh"] body {
  letter-spacing: 0.01em;
}

/* ---------- sections ---------- */

section {
  padding-block: clamp(2.5rem, 6vw, 4rem);
}

section + section {
  border-top: 1px solid var(--line);
}

h2 {
  font-family: var(--font-display);
  font-size: 1.35rem;
  font-weight: 600;
  letter-spacing: -0.01em;
  margin-bottom: 1.4rem;
  display: flex;
  align-items: baseline;
  gap: 0.8rem;
}

h2 .index {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 500;
  color: var(--cyan);
  letter-spacing: 0.16em;
}

p {
  color: var(--muted);
  margin-bottom: 1.1rem;
}

p:last-child {
  margin-bottom: 0;
}

p strong {
  color: var(--text);
  font-weight: 500;
}

/* ---------- intro ---------- */

.intro {
  padding-top: clamp(3.5rem, 9vh, 6rem);
  position: relative;
}

.code-eyebrow {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--cyan);
  letter-spacing: 0.06em;
  margin-bottom: 1.1rem;
}

.intro h1 {
  font-family: var(--font-display);
  font-size: clamp(2rem, 5.5vw, 3rem);
  font-weight: 700;
  line-height: 1.12;
  letter-spacing: -0.025em;
  margin-bottom: 1.75rem;
  max-width: 16ch;
}

.intro h1 em {
  font-style: normal;
  color: var(--cyan);
}

.intro-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: clamp(1.5rem, 4vw, 3rem);
  align-items: center;
}

.intro-photo {
  padding-top: 0.5rem;
  text-align: center;
}

.photo-stack {
  position: relative;
  display: inline-block;
}

.intro-photo .portrait {
  width: clamp(200px, 26vw, 256px);
  height: auto;
}

/* the little robot peeks over the portrait's corner */
.hero-mark {
  position: absolute;
  right: -18px;
  bottom: -14px;
  line-height: 0;
}

.hero-mark .coco-mark {
  width: clamp(56px, 8vw, 72px);
  height: auto;
  filter: drop-shadow(0 10px 24px rgba(4, 12, 18, 0.6));
}

.mark-note {
  margin-top: 0.9rem;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--faint);
  letter-spacing: 0.05em;
}

.portrait {
  border-radius: var(--radius-card);
  border: 1px solid var(--line);
  box-shadow: 0 24px 60px var(--dusk-glow);
}

.coco-mark .pupils {
  transition: transform 0.18s ease-out;
}

.coco-mark .pupil {
  transform-origin: center;
  transform-box: fill-box;
  animation: blink 5.4s infinite;
}

@keyframes blink {
  0%, 94%, 100% { transform: scaleY(1); }
  96.5% { transform: scaleY(0.08); }
}

@media (max-width: 560px) {
  .brand .zh {
    display: none;
  }
  .top-links {
    gap: 0.9rem;
    font-size: 0.75rem;
  }
  .intro-grid {
    grid-template-columns: 1fr;
  }
  .intro-photo {
    order: -1;
  }
  .intro-photo .portrait {
    width: clamp(150px, 40vw, 200px);
  }
}

/* ---------- teach-by-demonstration demo ---------- */
/* Draw a path in the panel; the robot replays it at once.
   In-context learning, as a toy. */

.demo-lede {
  color: var(--muted);
  margin-bottom: 1.1rem;
}

.teach {
  position: relative;
  height: 240px;
  border: 1px solid var(--line);
  border-radius: var(--radius-card);
  background-image: radial-gradient(var(--cyan-soft) 1px, transparent 1px);
  background-size: 22px 22px;
  cursor: crosshair;
  touch-action: none;
  overflow: hidden;
}

.teach-canvas {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
}

.teach-trace {
  fill: none;
  stroke: var(--cyan-a55);
  stroke-width: 3;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.teach-bot {
  position: absolute;
  left: 0;
  top: 0;
  width: 44px;
  height: 44px;
  margin: -22px 0 0 -22px;
  pointer-events: none;
  will-change: transform;
}

.teach-bot .coco-mark {
  width: 44px;
  height: auto;
  filter: drop-shadow(0 8px 18px var(--cyan-a25));
}

.teach-obstacles rect {
  fill: rgba(154, 176, 186, 0.1);
  stroke: rgba(154, 176, 186, 0.35);
  stroke-width: 1.5;
}

.goal-pad {
  fill: rgba(200, 139, 240, 0.08);
  stroke: var(--dusk-a55);
  stroke-width: 1.5;
}

.goal-bolt {
  fill: var(--dusk);
}

.teach-goal.lit {
  filter: drop-shadow(0 0 12px rgba(200, 139, 240, 0.9));
}

.teach-bot.bump .coco-mark {
  animation: bump 0.45s ease;
}

@keyframes bump {
  0% { transform: translateX(0); }
  25% { transform: translateX(-5px) rotate(-4deg); }
  55% { transform: translateX(4px) rotate(3deg); }
  100% { transform: none; }
}

.teach-status {
  margin-top: 0.9rem;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--faint);
  letter-spacing: 0.05em;
}


@media (max-width: 560px) {
  .teach {
    height: 200px;
  }
}

/* ---------- coco ---------- */

.coco-logo {
  width: min(230px, 60%);
  margin: 0.4rem 0 1.5rem;
}

.co-words {
  color: var(--muted);
}

.co-words b {
  color: var(--cyan);
  font-weight: 500;
}

/* ---------- training log ---------- */

.log {
  list-style: none;
  display: grid;
  gap: 1.4rem;
}

.log li {
  display: grid;
  grid-template-columns: 6.5rem minmax(0, 1fr);
  gap: 1.25rem;
  align-items: baseline;
}

.log .years {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--faint);
  letter-spacing: 0.06em;
  text-align: right;
}

.log .years.now {
  color: var(--cyan);
}

.log .what {
  color: var(--muted);
  font-size: 1rem;
}

.log .what strong {
  color: var(--text);
  font-weight: 500;
}

.log .phase {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 500;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--cyan);
  display: block;
  margin-bottom: 0.15rem;
}

@media (max-width: 560px) {
  .log li {
    grid-template-columns: 1fr;
    gap: 0.2rem;
  }
  .log .years {
    text-align: left;
  }
}

/* ---------- research ---------- */

.pubs {
  list-style: none;
  display: grid;
  gap: 1.1rem;
}

.pubs li {
  line-height: 1.5;
}

.pubs a {
  color: var(--text);
  font-weight: 500;
}

.pubs a:hover {
  color: var(--cyan);
  text-decoration: underline;
  text-underline-offset: 3px;
}

.pubs .meta {
  display: block;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--faint);
  letter-spacing: 0.05em;
  margin-top: 0.15rem;
}

/* ---------- footer ---------- */

.footer {
  border-top: 1px solid var(--line);
  padding-block: clamp(2.5rem, 6vw, 4rem) 3rem;
}

.footer .hello {
  font-family: var(--font-display);
  font-size: 1.2rem;
  font-weight: 600;
  margin-bottom: 0.4rem;
}

.footer-links {
  list-style: none;
  display: flex;
  gap: 1.25rem;
  margin: 1rem 0 1.75rem;
  font-family: var(--font-mono);
  font-size: 0.8rem;
}

.footer-links a {
  color: var(--muted);
}

.footer-links a:hover {
  color: var(--cyan);
  text-decoration: none;
}

.footer .fine {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--faint);
  letter-spacing: 0.05em;
}

/* ---------- scroll reveal ---------- */
/* Hidden state only applies when JS is running (html.js is stamped by an
   inline script in <head>), so a no-JS visit still sees the whole page. */

html.js .reveal {
  opacity: 0;
  transform: translateY(14px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

html.js .reveal.is-visible {
  opacity: 1;
  transform: none;
}

@media (prefers-reduced-motion: reduce) {
  html.js .reveal {
    opacity: 1;
    transform: none;
    transition: none;
  }
  .coco-mark .pupil {
    animation: none;
  }
  .coco-mark .pupils {
    transition: none;
  }
  .teach-bot.bump .coco-mark {
    animation: none;
  }
}