/* ============================================================
   Yizhou Lu — personal site
   Palette
     paper    #F6F7F4   cool near-white ground
     ink      #16211C   green-black text
     fresh    #2E7D4F   FreshLens green (CV / internship)
     orbit    #5A4FBF   JobSignal indigo (LLM / solo work)
     amber    #C4740B   instrument warning accent (used sparingly)
     line     #D9DED7   rules and borders
   Type
     display  Archivo (condensed-ish widths, heavy weights)
     body     IBM Plex Sans
     utility  IBM Plex Mono (numbers, labels, roles)
   ============================================================ */

:root {
  --paper: #F6F7F4;
  --paper-raise: #FFFFFF;
  --ink: #16211C;
  --ink-soft: #4A5650;
  --fresh: #2E7D4F;
  --fresh-tint: #E5F0E9;
  --orbit: #5A4FBF;
  --orbit-tint: #EAE8F7;
  --amber: #C4740B;
  --teal: #0E7C86;
  --teal-tint: #E2F0F1;
  --gold: #A8820A;
  --gold-tint: #F5EEDA;
  --line: #D9DED7;
  --human-job: #A8B5AE;
  --sel-ink: #FFFFFF;
  --display: "Archivo", sans-serif;
  --body: "IBM Plex Sans", sans-serif;
  --mono: "IBM Plex Mono", monospace;
  --maxw: 1080px;
}

/* Dark theme: accents brightened for contrast on the dark ground.
   Applies on system preference unless overridden by data-theme,
   and on data-theme="dark" regardless of system preference. */
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --paper: #101614;
    --paper-raise: #18201C;
    --ink: #E4EAE3;
    --ink-soft: #9AA8A0;
    --fresh: #55AB7C;
    --fresh-tint: #1B2E24;
    --orbit: #9C8FF2;
    --orbit-tint: #221F3A;
    --amber: #E09A3C;
    --teal: #4FB3BD;
    --teal-tint: #152E35;
    --gold: #D9B84A;
    --gold-tint: #2D2916;
    --line: #2B3630;
    --human-job: #5A6B62;
    --sel-ink: #1A1430;
  }
}
:root[data-theme="dark"] {
  --paper: #101614;
  --paper-raise: #18201C;
  --ink: #E4EAE3;
  --ink-soft: #9AA8A0;
  --fresh: #55AB7C;
  --fresh-tint: #1B2E24;
  --orbit: #9C8FF2;
  --orbit-tint: #221F3A;
  --amber: #E09A3C;
  --teal: #4FB3BD;
  --teal-tint: #152E35;
  --gold: #D9B84A;
  --gold-tint: #2D2916;
  --line: #2B3630;
  --human-job: #5A6B62;
  --sel-ink: #1A1430;
}

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

html { scroll-behavior: smooth; }

body {
  background: var(--paper);
  color: var(--ink);
  font-family: var(--body);
  font-size: 1.0625rem;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

::selection { background: var(--orbit); color: var(--sel-ink); }

a { color: inherit; }

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

/* keep anchored sections clear of the sticky header */
section[id] { scroll-margin-top: 4.5rem; }

/* skip-to-content: hidden until keyboard focus */
.skip-link {
  position: absolute;
  left: 1rem;
  top: -4rem;
  z-index: 100;
  font-family: var(--mono);
  font-size: 0.8rem;
  font-weight: 600;
  text-decoration: none;
  background: var(--ink);
  color: var(--paper);
  padding: 0.5rem 0.9rem;
  border-radius: 4px;
  transition: top 0.15s;
}
.skip-link:focus-visible { top: 0.75rem; }

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

.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 2rem;
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 1rem 1.5rem;
  background: color-mix(in srgb, var(--paper) 88%, transparent);
  backdrop-filter: blur(8px);
}

.wordmark {
  font-family: var(--display);
  font-weight: 900;
  font-size: 1.35rem;
  letter-spacing: -0.03em;
  text-decoration: none;
}
.wordmark-dot { color: var(--fresh); }

.site-nav {
  display: flex;
  gap: 1.4rem;
  margin-left: auto;
}
.site-nav a {
  font-family: var(--mono);
  font-size: 0.8rem;
  text-decoration: none;
  color: var(--ink-soft);
  padding: 0.2rem 0;
  border-bottom: 2px solid transparent;
  transition: color 0.15s, border-color 0.15s;
}
.site-nav a:hover { color: var(--ink); border-color: var(--fresh); }
.site-nav a.active { color: var(--ink); border-bottom-color: var(--fresh); }

.lang-switch {
  display: flex;
  align-items: center;
  gap: 0.45rem;
  font-family: var(--mono);
  font-size: 0.8rem;
}
.lang-switch a {
  text-decoration: none;
  color: var(--ink-soft);
  padding: 0.15rem 0;
  border-bottom: 2px solid transparent;
}
.lang-switch a:hover { color: var(--ink); }
.lang-switch a.active {
  color: var(--ink);
  font-weight: 600;
  border-bottom-color: var(--fresh);
}
.lang-switch .lang-sep { color: var(--line); }

/* Chinese page: CJK fallbacks slot in behind the latin faces */
body.zh {
  --display: "Archivo", "Noto Sans SC", sans-serif;
  --body: "IBM Plex Sans", "Noto Sans SC", sans-serif;
  --mono: "IBM Plex Mono", "Noto Sans SC", monospace;
  font-family: var(--body);
}
body.zh .hero-title { letter-spacing: 0; }

.header-cta {
  font-family: var(--mono);
  font-size: 0.8rem;
  font-weight: 600;
  text-decoration: none;
  color: var(--paper);
  background: var(--ink);
  padding: 0.5rem 0.95rem;
  border-radius: 4px;
  transition: background 0.15s;
}
.header-cta:hover { background: var(--orbit); }

.theme-toggle {
  font-family: var(--mono);
  font-size: 0.85rem;
  line-height: 1;
  color: var(--ink-soft);
  background: transparent;
  border: 1px solid var(--line);
  border-radius: 4px;
  padding: 0.45rem 0.6rem;
  cursor: pointer;
  transition: color 0.15s, border-color 0.15s;
}
.theme-toggle:hover { color: var(--ink); border-color: var(--ink-soft); }

/* ---------- hero ---------- */

.hero {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 5.5rem 1.5rem 4.5rem;
}

.hero-eyebrow {
  font-family: var(--mono);
  font-size: 0.85rem;
  color: var(--fresh);
  font-weight: 600;
  margin-bottom: 1.4rem;
}

.hero-title {
  font-family: var(--display);
  font-weight: 900;
  font-stretch: 82%;
  font-size: clamp(2.6rem, 7.2vw, 5.2rem);
  line-height: 1.02;
  letter-spacing: -0.025em;
  text-wrap: balance;
}
.hero-title span { display: block; }
.hero-title em {
  font-style: normal;
  color: var(--orbit);
  position: relative;
}
.hero-title em::after {
  content: "";
  position: absolute;
  left: 0; right: 0; bottom: 0.08em;
  height: 0.09em;
  background: var(--orbit);
  opacity: 0.35;
}

.hero-sub {
  max-width: 46rem;
  margin-top: 1.6rem;
  font-size: 1.15rem;
  color: var(--ink-soft);
}

.hero-links {
  display: flex;
  flex-wrap: wrap;
  gap: 1.6rem;
  margin-top: 1.8rem;
}
.hero-links a {
  font-family: var(--mono);
  font-size: 0.88rem;
  font-weight: 600;
  text-decoration: none;
  border-bottom: 2px solid var(--line);
  padding-bottom: 2px;
  transition: border-color 0.15s;
}
.hero-links a:hover { border-color: var(--fresh); }

/* ticker — instrument readout strip */

.ticker {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  border-top: 1px solid var(--ink);
  border-bottom: 1px solid var(--ink);
  margin-top: 3.4rem;
}
.ticker-item {
  padding: 1.1rem 1.2rem 1.1rem 0;
  border-right: 1px solid var(--line);
  display: flex;
  flex-direction: column;
}
.ticker-item:last-child { border-right: none; }
.ticker-num, .ticker-mono {
  font-family: var(--mono);
  font-weight: 600;
  font-size: 1.7rem;
  line-height: 1.1;
  font-variant-numeric: tabular-nums;
}
.ticker-plus {
  font-family: var(--mono);
  font-weight: 600;
  font-size: 1.7rem;
  line-height: 1.1;
  display: inline;
}
.ticker-item { flex-direction: row; flex-wrap: wrap; align-items: baseline; column-gap: 0.05em; }
.ticker-label {
  flex-basis: 100%;
  font-family: var(--mono);
  font-size: 0.72rem;
  color: var(--ink-soft);
  margin-top: 0.45rem;
  line-height: 1.4;
}

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

.section {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 4.5rem 1.5rem;
}

.section-head { margin-bottom: 2.6rem; }

.section-head h2, .contact-title {
  font-family: var(--display);
  font-weight: 800;
  font-stretch: 85%;
  font-size: clamp(1.9rem, 4vw, 2.7rem);
  letter-spacing: -0.02em;
  line-height: 1.1;
}

.section-sub {
  margin-top: 0.7rem;
  color: var(--ink-soft);
  max-width: 44rem;
}

/* ---------- projects ---------- */

.project {
  background: var(--paper-raise);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 2.2rem 2.4rem;
  margin-bottom: 1.6rem;
  position: relative;
  overflow: hidden;
}
.project::before {
  content: "";
  position: absolute;
  left: 0; top: 0; bottom: 0;
  width: 5px;
}
.project--signal::before { background: var(--orbit); }
.project--fresh::before { background: var(--fresh); }
.project--gothin::before { background: var(--teal); }
.project--lumen::before { background: var(--gold); }

/* whole-card click target: the title anchor stretches over the card */
.project--link .project-title a.stretch::after {
  content: "";
  position: absolute;
  inset: 0;
  z-index: 1;
}
.project--link {
  transition: border-color 0.15s, transform 0.15s, box-shadow 0.15s;
}
.project--link:hover {
  border-color: var(--ink);
  transform: translateY(-2px);
  box-shadow: 0 8px 24px rgba(22, 33, 28, 0.08);
}
.project-visit {
  position: absolute;
  top: 1.1rem;
  right: 1.3rem;
  font-family: var(--mono);
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--ink-soft);
  opacity: 0.55;
  transition: opacity 0.15s, color 0.15s;
}
.project--link:hover .project-visit { opacity: 1; color: var(--ink); }

.project-meta {
  display: flex;
  align-items: center;
  gap: 1rem;
  margin-bottom: 1rem;
}
.chip {
  font-family: var(--mono);
  font-size: 0.72rem;
  font-weight: 600;
  padding: 0.25rem 0.6rem;
  border-radius: 3px;
}
.chip--indigo { background: var(--orbit-tint); color: var(--orbit); }
.chip--green { background: var(--fresh-tint); color: var(--fresh); }
.chip--teal { background: var(--teal-tint); color: var(--teal); }
.chip--gold { background: var(--gold-tint); color: var(--gold); }
.project-dates {
  font-family: var(--mono);
  font-size: 0.78rem;
  color: var(--ink-soft);
}

.project-title {
  font-family: var(--display);
  font-weight: 800;
  font-size: 1.9rem;
  letter-spacing: -0.02em;
}
.project-title a { text-decoration: none; }
.project-title a:hover { color: var(--orbit); }

.project-tag {
  color: var(--ink-soft);
  margin-top: 0.25rem;
  margin-bottom: 1.2rem;
}

.project-body p { max-width: 48rem; }

.project-points {
  margin: 1.1rem 0 0 0;
  padding: 0;
  list-style: none;
  max-width: 50rem;
}
.project-points li {
  padding: 0.55rem 0 0.55rem 1.5rem;
  position: relative;
  border-top: 1px dashed var(--line);
}
.project-points li::before {
  content: "▸";
  position: absolute;
  left: 0.2rem;
  color: var(--amber);
}

.project-stack {
  margin-top: 1.4rem;
  font-family: var(--mono);
  font-size: 0.78rem;
  color: var(--ink-soft);
}

.project-row {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: 1.6rem;
  margin-top: 0.4rem;
}
.mini-project {
  border-top: 2px solid var(--ink);
  padding-top: 1rem;
  max-width: 44rem;
}
.mini-project h4 {
  font-family: var(--display);
  font-weight: 800;
  font-size: 1.15rem;
  margin-bottom: 0.5rem;
}
.mini-project h4 a { text-decoration: none; }
.mini-project h4 a:hover { color: var(--orbit); }
.mini-project p { font-size: 0.95rem; color: var(--ink-soft); }
.mini-stack {
  margin-top: 0.7rem;
  font-family: var(--mono);
  font-size: 0.72rem;
}

/* ---------- pipeline (signature) ---------- */

.section--pipeline {
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
}

.pipeline {
  display: flex;
  flex-wrap: wrap;
  align-items: stretch;
  gap: 0.5rem;
  margin-bottom: 0.8rem;
}

.pipe-node {
  position: relative;
  flex: 1 1 120px;
  min-width: 118px;
  background: var(--paper-raise);
  border: 1px solid var(--line);
  border-radius: 6px;
  padding: 0.85rem 0.9rem;
  cursor: default;
  transition: border-color 0.15s, transform 0.15s, box-shadow 0.15s;
  opacity: 0;
  transform: translateY(10px);
}
.pipeline.lit .pipe-node {
  animation: node-in 0.4s ease forwards;
}
.pipeline.lit .pipe-node:nth-child(1)  { animation-delay: 0.00s; }
.pipeline.lit .pipe-node:nth-child(3)  { animation-delay: 0.12s; }
.pipeline.lit .pipe-node:nth-child(5)  { animation-delay: 0.24s; }
.pipeline.lit .pipe-node:nth-child(7)  { animation-delay: 0.36s; }
.pipeline.lit .pipe-node:nth-child(9)  { animation-delay: 0.48s; }
.pipeline.lit .pipe-node:nth-child(11) { animation-delay: 0.60s; }
.pipeline.lit .pipe-node:nth-child(13) { animation-delay: 0.72s; }

@keyframes node-in {
  to { opacity: 1; transform: translateY(0); }
}

.pipe-node:hover, .pipe-node:focus-visible {
  border-color: var(--orbit);
  transform: translateY(-2px);
  box-shadow: 0 6px 18px rgba(90, 79, 191, 0.12);
}
.pipe-node--review { border-style: dashed; border-color: var(--amber); }
.pipe-node--human { background: var(--ink); }
.pipe-node--human .pipe-role { color: var(--paper); }
.pipe-node--human .pipe-job { color: var(--human-job); }

.pipe-role {
  display: block;
  font-family: var(--mono);
  font-size: 0.72rem;
  font-weight: 600;
  color: var(--orbit);
}
.pipe-node--review .pipe-role { color: var(--amber); }
.pipe-job {
  display: block;
  font-size: 0.82rem;
  color: var(--ink-soft);
  margin-top: 0.2rem;
  line-height: 1.35;
}

.pipe-arrow {
  align-self: center;
  color: var(--ink-soft);
  font-size: 0.9rem;
  opacity: 0;
}
.pipeline.lit .pipe-arrow { animation: node-in 0.3s ease forwards; }
.pipeline.lit .pipe-arrow:nth-child(2)  { animation-delay: 0.08s; }
.pipeline.lit .pipe-arrow:nth-child(4)  { animation-delay: 0.20s; }
.pipeline.lit .pipe-arrow:nth-child(6)  { animation-delay: 0.32s; }
.pipeline.lit .pipe-arrow:nth-child(8)  { animation-delay: 0.44s; }
.pipeline.lit .pipe-arrow:nth-child(10) { animation-delay: 0.56s; }
.pipeline.lit .pipe-arrow:nth-child(12) { animation-delay: 0.68s; }

/* hover card */
.pipe-card {
  position: absolute;
  left: 50%;
  bottom: calc(100% + 10px);
  transform: translateX(-50%) translateY(4px);
  width: 250px;
  background: var(--ink);
  color: var(--paper);
  font-size: 0.82rem;
  line-height: 1.5;
  padding: 0.85rem 1rem;
  border-radius: 6px;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.15s, transform 0.15s;
  z-index: 20;
}
.pipe-card::after {
  content: "";
  position: absolute;
  top: 100%;
  left: 50%;
  transform: translateX(-50%);
  border: 6px solid transparent;
  border-top-color: var(--ink);
}
.pipe-node:hover .pipe-card,
.pipe-node:focus-visible .pipe-card {
  opacity: 1;
  transform: translateX(-50%) translateY(0);
}

.pipe-loop-note {
  font-family: var(--mono);
  font-size: 0.75rem;
  color: var(--amber);
  margin-bottom: 2.8rem;
}

/* rules */

.rules-title {
  font-family: var(--display);
  font-weight: 800;
  font-size: 1.25rem;
  margin-bottom: 1.2rem;
}
.rules-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(230px, 1fr));
  gap: 1px;
  background: var(--line);
  border: 1px solid var(--line);
  border-radius: 6px;
  overflow: hidden;
}
.rule {
  background: var(--paper-raise);
  padding: 1.1rem 1.2rem;
  font-size: 0.92rem;
  color: var(--ink-soft);
}
.rule-k {
  display: block;
  font-family: var(--mono);
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--ink);
  margin-bottom: 0.3rem;
}

/* ---------- timeline ---------- */

.timeline {
  list-style: none;
  border-left: 2px solid var(--line);
  padding-left: 0;
  margin-left: 0.4rem;
}
.tl-item {
  display: grid;
  grid-template-columns: 150px 1fr;
  gap: 1.6rem;
  padding: 0 0 2.2rem 1.8rem;
  position: relative;
}
.tl-item::before {
  content: "";
  position: absolute;
  left: -6px;
  top: 0.5em;
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: var(--paper);
  border: 2px solid var(--fresh);
}
.tl-item:first-child::before { background: var(--fresh); }
.tl-when {
  font-family: var(--mono);
  font-size: 0.8rem;
  color: var(--ink-soft);
  padding-top: 0.2em;
  white-space: nowrap;
}
.tl-what h3 {
  font-family: var(--display);
  font-weight: 700;
  font-size: 1.15rem;
  letter-spacing: -0.01em;
}
.tl-what p {
  margin-top: 0.35rem;
  color: var(--ink-soft);
  font-size: 0.97rem;
  max-width: 44rem;
}

.edu {
  display: flex;
  flex-wrap: wrap;
  gap: 2.5rem;
  margin-top: 1.4rem;
  padding-top: 1.6rem;
  border-top: 1px solid var(--line);
}
.edu-item { display: flex; flex-direction: column; }
.edu-school { font-weight: 600; }
.edu-degree {
  font-family: var(--mono);
  font-size: 0.78rem;
  color: var(--ink-soft);
  margin-top: 0.2rem;
}

/* ---------- contact ---------- */

.section--contact {
  text-align: center;
  padding-top: 5.5rem;
  padding-bottom: 5.5rem;
}
.contact-sub {
  color: var(--ink-soft);
  margin-top: 0.8rem;
}
.contact-links {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.9rem;
  margin-top: 2rem;
}
.contact-primary {
  font-family: var(--mono);
  font-weight: 600;
  font-size: clamp(1.1rem, 3vw, 1.6rem);
  text-decoration: none;
  color: var(--paper);
  background: var(--ink);
  padding: 0.8rem 1.6rem;
  border-radius: 6px;
  transition: background 0.15s;
}
.contact-primary:hover { background: var(--orbit); }
.contact-links a:not(.contact-primary) {
  font-family: var(--mono);
  font-size: 0.85rem;
  color: var(--ink-soft);
}

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

.site-footer {
  border-top: 1px solid var(--line);
  padding: 1.6rem 1.5rem;
  text-align: center;
  font-family: var(--mono);
  font-size: 0.75rem;
  color: var(--ink-soft);
}

/* ---------- reveal animation ---------- */

.reveal {
  opacity: 0;
  transform: translateY(14px);
  animation: rise 0.6s cubic-bezier(0.2, 0.7, 0.3, 1) forwards;
}
.reveal.d1 { animation-delay: 0.08s; }
.reveal.d2 { animation-delay: 0.16s; }
.reveal.d3 { animation-delay: 0.28s; }
.reveal.d4 { animation-delay: 0.36s; }
.reveal.d5 { animation-delay: 0.46s; }

@keyframes rise {
  to { opacity: 1; transform: translateY(0); }
}

.scroll-reveal {
  opacity: 0;
  transform: translateY(18px);
  transition: opacity 0.55s ease, transform 0.55s ease;
}
.scroll-reveal.in {
  opacity: 1;
  transform: translateY(0);
}

/* ---------- responsive ---------- */

@media (max-width: 760px) {
  .site-header { gap: 0.6rem 1.1rem; padding: 0.7rem 1rem; }
  /* nav becomes a second, horizontally scrollable row instead of vanishing */
  .site-nav {
    display: flex;
    order: 3;
    flex-basis: 100%;
    margin-left: 0;
    gap: 1.1rem;
    overflow-x: auto;
    scrollbar-width: none;
    padding-bottom: 0.15rem;
  }
  .site-nav::-webkit-scrollbar { display: none; }
  .site-nav a { white-space: nowrap; }
  .lang-switch { margin-left: auto; }
  section[id] { scroll-margin-top: 7rem; }
  .project { padding: 1.6rem 1.4rem; }
  .tl-item { grid-template-columns: 1fr; gap: 0.3rem; }
  .pipe-arrow { display: none; }
  /* pipeline stacks vertically; station details render inline, not as hover cards */
  .pipe-node { flex-basis: 100%; }
  .pipe-card {
    position: static;
    transform: none;
    width: auto;
    background: transparent;
    color: var(--ink-soft);
    padding: 0.55rem 0 0;
    margin-top: 0.55rem;
    border-top: 1px dashed var(--line);
    border-radius: 0;
    opacity: 1;
  }
  .pipe-card::after { display: none; }
  .pipe-node--human .pipe-card { color: var(--human-job); }
  .pipe-job { font-size: 0.78rem; }
}

@media (max-width: 420px) {
  .header-cta { padding: 0.45rem 0.7rem; }
  .wordmark { font-size: 1.2rem; }
}

/* ---------- reduced motion ---------- */

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .reveal, .pipeline .pipe-node, .pipeline .pipe-arrow {
    animation: none !important;
    opacity: 1 !important;
    transform: none !important;
  }
  .scroll-reveal { opacity: 1; transform: none; transition: none; }
  .pipe-node, .pipe-card { transition: none; }
}