/* ==========================================================================
   Junwei Quan — personal site
   Hand-built. Editorial serif: Source Serif 4 display, Inter body,
   JetBrains Mono for dates, venues and labels.
   ========================================================================== */

/* --- Palette -------------------------------------------------------------
   Every token is defined here in the base :root so no colour exists only
   inside a media query or a [data-theme] block. */
:root {
  --paper:        #fdfbf6;
  --paper-sunk:   #f5f1e8;
  --ink:          #1b1a17;
  --ink-soft:     #46433c;
  --ink-muted:    #7a756a;
  --rule:         #e3ddd0;
  --rule-strong:  #cec7b6;
  --accent:       #8c4227;
  --accent-soft:  #b8674a;
  --selection:    #f0e2d4;

  --font-display: "Source Serif 4", Georgia, "Times New Roman", serif;
  --font-body:    "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
  --font-mono:    "JetBrains Mono", ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;

  --measure: 780px;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --paper:        #15140f;
    --paper-sunk:   #1d1b15;
    --ink:          #ece8dd;
    --ink-soft:     #c3bdaf;
    --ink-muted:    #918a7b;
    --rule:         #2f2c24;
    --rule-strong:  #45402f;
    --accent:       #e09a72;
    --accent-soft:  #c47c55;
    --selection:    #3a2a1d;
  }
}

:root[data-theme="dark"] {
  --paper:        #15140f;
  --paper-sunk:   #1d1b15;
  --ink:          #ece8dd;
  --ink-soft:     #c3bdaf;
  --ink-muted:    #918a7b;
  --rule:         #2f2c24;
  --rule-strong:  #45402f;
  --accent:       #e09a72;
  --accent-soft:  #c47c55;
  --selection:    #3a2a1d;
}

/* --- Reset ---------------------------------------------------------------- */
*, *::before, *::after { box-sizing: border-box; }

html {
  scroll-behavior: smooth;
  scroll-padding-top: 5rem;
  -webkit-text-size-adjust: 100%;
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--font-body);
  font-size: 16.5px;
  line-height: 1.68;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

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

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

h1, h2, h3, h4 { font-family: var(--font-display); font-weight: 600; line-height: 1.22; }

p { margin: 0 0 1.05em; }

ul, ol { margin: 0; padding: 0; list-style: none; }

code {
  font-family: var(--font-mono);
  font-size: 0.86em;
  background: var(--paper-sunk);
  padding: 0.1em 0.35em;
  border-radius: 3px;
}

/* --- Links ---------------------------------------------------------------- */
a {
  color: var(--accent);
  text-decoration: none;
  border-bottom: 1px solid transparent;
  transition: border-color 120ms ease, color 120ms ease;
}

a:hover { border-bottom-color: var(--accent-soft); }

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

.skip-link {
  position: absolute;
  left: -9999px;
  top: 0;
  background: var(--paper);
  padding: 0.6rem 1rem;
  z-index: 100;
}

.skip-link:focus {
  left: 1rem;
  top: 1rem;
}

/* --- Navigation ----------------------------------------------------------- */
.nav {
  position: sticky;
  top: 0;
  z-index: 50;
  background: color-mix(in srgb, var(--paper) 88%, transparent);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--rule);
}

/* The bar spans the window; its contents line up with the content column. */
.nav-inner {
  max-width: var(--measure);
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 0.85rem 2rem;
}

.nav ul {
  display: flex;
  flex-wrap: wrap;
  gap: 1.4rem;
}

.nav a {
  font-family: var(--font-mono);
  font-size: 0.775rem;
  letter-spacing: 0.04em;
  text-transform: lowercase;
  color: var(--ink-muted);
}

.nav a:hover { color: var(--ink); }

.nav a.is-current {
  color: var(--ink);
  border-bottom-color: var(--rule-strong);
}

.theme-toggle {
  flex: none;
  width: 1.5rem;
  height: 1.5rem;
  padding: 0;
  border: 1px solid var(--rule-strong);
  border-radius: 50%;
  background:
    linear-gradient(to right, var(--ink) 0 50%, transparent 50% 100%);
  cursor: pointer;
  transition: transform 160ms ease, border-color 120ms ease;
}

.theme-toggle:hover { transform: rotate(180deg); border-color: var(--accent); }

.theme-toggle:focus-visible { outline: 2px solid var(--accent); outline-offset: 3px; }

/* --- Layout --------------------------------------------------------------- */
main {
  max-width: var(--measure);
  margin: 0 auto;
  padding: 0 2rem;
}

section {
  padding: 3.2rem 0;
  border-top: 1px solid var(--rule);
}

section > h2 {
  font-size: 0.8rem;
  font-family: var(--font-mono);
  font-weight: 500;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--ink-muted);
  margin: 0 0 1.9rem;
}

/* --- Intro ---------------------------------------------------------------- */
.intro {
  display: grid;
  grid-template-columns: 1fr 208px;
  gap: 3rem;
  align-items: start;
  padding: 4.2rem 0 3.4rem;
}

.intro h1 {
  font-size: 2.85rem;
  letter-spacing: -0.018em;
  margin: 0 0 0.5rem;
}

.intro .affil {
  font-family: var(--font-mono);
  font-size: 0.82rem;
  line-height: 1.6;
  color: var(--ink-muted);
  margin-bottom: 1.9rem;
  padding-bottom: 1.6rem;
  border-bottom: 1px solid var(--rule);
}

.intro .affil a { color: var(--ink-soft); border-bottom-color: var(--rule-strong); }
.intro .affil a:hover { color: var(--accent); border-bottom-color: var(--accent-soft); }

.intro-text p { color: var(--ink-soft); }

.intro-text strong { color: var(--ink); font-weight: 600; }

.intro-photo img {
  width: 100%;
  /* height:auto is load-bearing — the img's height attribute is a presentational
     hint that would otherwise beat aspect-ratio and render at intrinsic height. */
  height: auto;
  aspect-ratio: 3 / 4;
  object-fit: cover;
  object-position: center 22%;
  border-radius: 3px;
  filter: saturate(0.92);
}

/* --- Link row ------------------------------------------------------------- */
.links {
  display: flex;
  flex-wrap: wrap;
  gap: 0 1.5rem;
  margin-top: 1.7rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--rule);
  font-family: var(--font-mono);
  font-size: 0.8rem;
}

.links a { border-bottom-color: var(--rule-strong); }

/* --- Research ------------------------------------------------------------- */
.lede {
  color: var(--ink-soft);
  font-size: 1.02rem;
  margin-bottom: 2.4rem;
}

.topic { margin-bottom: 2.5rem; }
.topic:last-child { margin-bottom: 0; }

.topic h3 {
  font-size: 1.22rem;
  margin: 0 0 0.6rem;
  color: var(--ink);
}

.topic p { color: var(--ink-soft); }

.topic-ref {
  font-family: var(--font-mono);
  font-size: 0.76rem;
  color: var(--ink-muted);
  margin-bottom: 0;
}

/* --- News ----------------------------------------------------------------- */
.news li {
  display: grid;
  grid-template-columns: 5.6rem 1fr;
  gap: 1rem;
  padding: 0.62rem 0;
  border-bottom: 1px dotted var(--rule);
  color: var(--ink-soft);
}

.news li:last-child { border-bottom: none; }

.date {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  color: var(--ink-muted);
  white-space: nowrap;
  padding-top: 0.15em;
}

/* --- Publications --------------------------------------------------------- */
.note {
  font-family: var(--font-mono);
  font-size: 0.74rem;
  color: var(--ink-muted);
  margin-top: -1.2rem;
  margin-bottom: 2rem;
}

/* Papers are grouped by area: a numbered heading and a one-line description,
   then that area's entries. */
.pub-group + .pub-group { margin-top: 3.6rem; }

.pub-group > h3 {
  display: flex;
  align-items: baseline;
  gap: 0.75rem;
  font-size: 1.3rem;
  margin: 0 0 0.3rem;
}

.group-num {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  font-weight: 500;
  color: var(--accent);
}

.group-desc {
  font-size: 0.93rem;
  color: var(--ink-muted);
  margin-bottom: 1.9rem;
  padding-bottom: 1.3rem;
  border-bottom: 1px solid var(--rule-strong);
}

.pubs > li {
  padding-bottom: 2rem;
  margin-bottom: 2rem;
  border-bottom: 1px solid var(--rule);
  scroll-margin-top: 5rem;
}

.pubs > li:last-child { border-bottom: none; margin-bottom: 0; padding-bottom: 0; }

.pubs h4 {
  font-size: 1.1rem;
  margin: 0 0 0.4rem;
  line-height: 1.34;
}

.authors {
  font-size: 0.92rem;
  color: var(--ink-soft);
  margin-bottom: 0.35rem;
}

.authors strong { color: var(--ink); font-weight: 600; }

.venue { margin-bottom: 0.85rem; }

.tag {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.7rem;
  letter-spacing: 0.05em;
  padding: 0.16rem 0.5rem;
  background: var(--paper-sunk);
  border: 1px solid var(--rule);
  border-radius: 3px;
  color: var(--ink-soft);
}

.status {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--ink-muted);
  margin-left: 0.35rem;
}

.tldr {
  font-size: 0.94rem;
  color: var(--ink-soft);
  margin-bottom: 0.6rem;
  padding-left: 1rem;
  border-left: 2px solid var(--rule);
}

.pub-links {
  display: flex;
  gap: 1.1rem;
  font-family: var(--font-mono);
  font-size: 0.76rem;
  margin-bottom: 0;
}

.also {
  font-size: 0.9rem;
  color: var(--ink-muted);
  margin-top: 2rem;
  margin-bottom: 0;
}

/* --- Experience & education ----------------------------------------------- */
.entry {
  padding-bottom: 1.9rem;
  margin-bottom: 1.9rem;
  border-bottom: 1px dotted var(--rule);
}

.entry:last-of-type { border-bottom: none; margin-bottom: 0; }

.entry > .date {
  display: block;
  margin-bottom: 0.3rem;
  padding-top: 0;
}

.entry h3 {
  font-size: 1.1rem;
  margin: 0 0 0.55rem;
}

.entry-sub {
  font-family: var(--font-body);
  font-size: 0.93rem;
  font-weight: 400;
  font-style: italic;
  color: var(--ink-muted);
}

p.entry-sub { margin-top: -0.3rem; }

.entry > p:not(.date):not(.entry-sub) {
  color: var(--ink-soft);
  font-size: 0.95rem;
  margin-bottom: 0;
}

/* --- Awards --------------------------------------------------------------- */
.awards {
  margin-top: 2.2rem;
  padding-top: 1.6rem;
  border-top: 1px solid var(--rule);
}

.awards li {
  display: grid;
  grid-template-columns: 5.6rem 1fr;
  gap: 1rem;
  padding: 0.42rem 0;
  color: var(--ink-soft);
  font-size: 0.95rem;
}

/* --- Footer --------------------------------------------------------------- */
footer {
  max-width: var(--measure);
  margin: 0 auto;
  padding: 0 2rem 4rem;
  font-family: var(--font-mono);
  font-size: 0.76rem;
  color: var(--ink-muted);
}

/* Rule sits inside the padding so it lines up with the section rules above. */
.footer-inner {
  padding-top: 2.4rem;
  border-top: 1px solid var(--rule);
}

footer p { margin-bottom: 0.5rem; }

footer a { border-bottom-color: var(--rule-strong); }

.colophon { color: var(--ink-muted); opacity: 0.75; margin-bottom: 0; }

/* --- Responsive ----------------------------------------------------------- */
@media (max-width: 720px) {
  body { font-size: 16px; }

  .nav-inner { padding: 0.7rem 1.25rem; }
  .nav ul { gap: 1rem; }
  .nav a { font-size: 0.72rem; }

  main { padding: 0 1.25rem; }
  footer { padding: 0 1.25rem 3rem; }
  .footer-inner { padding-top: 2rem; }

  .intro {
    grid-template-columns: 1fr;
    gap: 2rem;
    padding: 2.6rem 0 2.6rem;
  }

  /* Photo above the name on narrow screens. */
  .intro-photo { order: -1; max-width: 168px; }

  .intro h1 { font-size: 2.25rem; }

  section { padding: 2.6rem 0; }

  .news li,
  .awards li {
    grid-template-columns: 1fr;
    gap: 0.15rem;
  }

  .tldr { padding-left: 0.85rem; }
}