/* ---------- Design tokens ---------- */
:root {
  color-scheme: light dark;

  /* colour */
  --bg: #ffffff;
  --surface: #f6f6f4;
  --text: #1f1f1f;
  --muted: #646464;
  --faint: #9a9a96;
  --rule: #e4e4e0;
  --link: #1a5fb4;
  --link-hover: #c4540a;
  --focus: #1a5fb4;
  --badge-bg: #eef2f8;
  --badge-border: #d3deec;
  --badge-text: #2b4a74;
  --status-dot: #2f9e5b;
  --mono-logo-filter: none;

  /* type: serif for reading, sans for titles and labels; system fonts only */
  --font-serif: ui-serif, "New York", "Iowan Old Style", "Palatino Linotype", Palatino, Georgia, Cambria, "Times New Roman", "Songti SC", "Noto Serif CJK SC", serif;
  --font-sans: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "PingFang SC", "Hiragino Sans GB", "Noto Sans CJK SC", "Microsoft YaHei", sans-serif;
  --fs-body: 17px;
  --fs-label: 14px;
  --fs-badge: 12.5px;
  --fs-h1: 30px;
  --fs-h2: 19px;
  --fs-h3: 16px;
  --lh-body: 1.6;
  --lh-tight: 1.35;

  /* space and layout */
  --measure: 780px;
  --gutter: 16px;
  --space-1: 4px;
  --space-2: 8px;
  --space-3: 12px;
  --space-4: 16px;
  --space-5: 24px;
  --space-6: 40px;
  --radius: 6px;
  --radius-portrait: 12px;
  --portrait: 168px;
  --thumb-w: 180px;

  /* motion */
  --dur: 150ms;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #121315;
    --surface: #1b1d20;
    --text: #e7e5e1;
    --muted: #a3a19c;
    --faint: #7a7874;
    --rule: #2c2e32;
    --link: #79b0f2;
    --link-hover: #f2a65a;
    --focus: #79b0f2;
    --badge-bg: #1d2633;
    --badge-border: #2f4360;
    --badge-text: #b5cdf0;
    --status-dot: #4cc27d;
    --mono-logo-filter: invert(1);   /* black Leeds square becomes white; its transparent tower stays see-through */
  }
}

/* ---------- Base ---------- */
* { box-sizing: border-box; }

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

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-serif);
  font-size: var(--fs-body);
  line-height: var(--lh-body);
}

main {
  max-width: calc(var(--measure) + 2 * var(--gutter));
  margin: 0 auto;
  padding: var(--space-6) var(--gutter) var(--space-5);
}

p { margin: 0 0 var(--space-3); }

a {
  color: var(--link);
  text-decoration: none;
  transition: color var(--dur) ease;
}
a:hover { color: var(--link-hover); text-decoration: underline; }
a:focus-visible, summary:focus-visible {
  outline: 2px solid var(--focus);
  outline-offset: 2px;
  border-radius: 2px;
}

/* Titles and labels use the sans stack */
h1, h2, h3,
.status, .links, .contact, .meta, .date, .badge, .venue,
.focus dt, .lab-name, .pub-title, .proj-title, .more summary, footer {
  font-family: var(--font-sans);
}

h1 { font-size: var(--fs-h1); font-weight: 600; line-height: 1.2; margin: 0 0 var(--space-2); }
section { margin-top: var(--space-6); padding-top: var(--space-4); border-top: 1px solid var(--rule); }
h2 { font-size: var(--fs-h2); font-weight: 600; margin: 0 0 var(--space-3); }
h3 { font-size: var(--fs-h3); font-weight: 600; line-height: var(--lh-tight); margin: 0 0 var(--space-1); }

.meta, .date, .contact { color: var(--muted); font-size: var(--fs-label); }
.links { font-size: var(--fs-label); }
.date { white-space: nowrap; font-weight: 400; }

/* ---------- Header ---------- */
.intro { display: flex; align-items: flex-start; gap: var(--space-5); }
.intro-text { flex: 1; min-width: 0; }
.intro-text > p:not([class]) { text-wrap: balance; text-wrap: pretty; }   /* bio: no one-word last line; balance where pretty is unsupported */
.intro-side { flex: 0 0 auto; display: flex; flex-direction: column; align-items: center; text-align: center; padding-top: 5px; }   /* portrait top sits on the h1 cap line */
.intro-side .links { margin: var(--space-3) 0 2px; }
.intro-side .contact { margin: 0; }
.portrait {
  flex: 0 0 auto;
  width: var(--portrait);
  height: var(--portrait);
  border-radius: var(--radius-portrait);
  object-fit: cover;
}

.status {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  margin-bottom: var(--space-4);
  padding: 3px var(--space-3);
  border: 1px solid var(--rule);
  border-radius: 999px;
  background: var(--surface);
  font-size: 13.5px;
  line-height: 1.4;
}
.status-dot {
  flex: 0 0 auto;
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--status-dot);
}

/* Education: one row per line, 20 px mark + 12 px gap + muted text (after the old site's rows) */
.edu {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
  margin: 0 0 var(--space-4);
  font-family: var(--font-sans);
  font-size: var(--fs-label);
  line-height: 1.4;
}
.edu-line { display: flex; align-items: flex-start; gap: var(--space-3); color: var(--muted); font-weight: 500; }   /* mark aligns with the first line, not the block centre */
.edu-grad { font-weight: 400; }
.edu-line > span { text-wrap: balance; }
.edu-part { display: inline-block; }   /* a long line breaks between parts, e.g. before "@ Southwest…" */
.edu-logo {
  flex: 0 0 auto;
  width: 20px;
  height: 20px;
  object-fit: contain;
  border-radius: 3px;
}
.edu-logo-mono { filter: var(--mono-logo-filter); }
.edu-icon { flex: 0 0 auto; width: 20px; height: 20px; color: var(--faint); }

/* Goal / interests / current question */
.focus {
  display: grid;
  grid-template-columns: max-content 1fr;
  gap: var(--space-1) var(--space-4);
  margin: var(--space-5) 0 0;
  padding: var(--space-3) var(--space-4);
  background: var(--surface);
  border-radius: var(--radius);
}
.focus dt { font-weight: 600; font-size: var(--fs-label); line-height: var(--lh-body); padding-top: 2px; }
.focus dd { margin: 0; }

/* ---------- Research ---------- */
.lab { margin-bottom: var(--space-3); }
.lab-name { font-weight: 600; margin-bottom: 0; }
.lab > .meta { margin-bottom: var(--space-2); }
.lab .entry { margin-left: 2px; padding-left: var(--space-4); border-left: 2px solid var(--rule); }

.entry { display: flex; gap: var(--space-4); padding: var(--space-3) 0; }
.thumb { flex: 0 0 var(--thumb-w); }
.thumb:empty { display: none; }
.lab .thumb:empty { display: block; }   /* keeps P2 text aligned with P1 inside the lab block */
.thumb img { display: block; width: var(--thumb-w); height: auto; border: 1px solid var(--rule); border-radius: var(--radius); }
.entry-text { flex: 1; min-width: 0; }
section > .entry h3 { font-size: var(--fs-body); }   /* top-level entry title = same size as .lab-name / .proj-title */
.takeaway { font-style: italic; }

/* ---------- Publications ---------- */
.pubs { list-style: none; padding: 0; margin: 0; }
.pubs li { margin-bottom: var(--space-4); }
.pubs p { margin-bottom: 2px; }
.pub-title { font-weight: 600; font-size: var(--fs-body); line-height: var(--lh-tight); }
.venue { color: var(--muted); font-size: var(--fs-label); overflow-wrap: anywhere; }
.badge {
  display: inline-block;
  margin-right: var(--space-1);
  padding: 0 7px;
  border: 1px solid var(--badge-border);
  border-radius: 4px;
  background: var(--badge-bg);
  color: var(--badge-text);
  font-size: var(--fs-badge);
  font-weight: 600;
  line-height: 1.6;
}
.pub-note { margin-top: var(--space-1); }

/* ---------- Honors ---------- */
.honors { list-style: none; padding: 0; margin: 0; }
.honors li { display: flex; justify-content: space-between; align-items: baseline; gap: var(--space-4); margin-bottom: var(--space-1); }

/* ---------- Projects, internship ---------- */
.projects { list-style: none; padding: 0; margin: 0; }
.projects li { margin-bottom: var(--space-4); }
.proj-title { font-weight: 600; }
.proj-head { font-family: var(--font-sans); }
.projects .links { display: block; }

.more summary { cursor: pointer; color: var(--link); font-size: var(--fs-label); margin-bottom: var(--space-3); transition: color var(--dur) ease; }
.more summary:hover { color: var(--link-hover); }

/* ---------- Consistent space above each section rule ---------- */
section > :last-child { margin-bottom: 0; }
.lab > :last-child, .entry-text > :last-child { margin-bottom: 0; }
section > .entry:last-child { padding-bottom: 0; }
section > :last-child > li:last-child { margin-bottom: 0; }   /* only the list that closes the section */
.pubs li:last-child > :last-child { margin-bottom: 0; }
.more summary { margin-bottom: 0; }
.more[open] summary { margin-bottom: var(--space-3); }

/* ---------- Footer ---------- */
footer { margin-top: var(--space-6); padding-top: var(--space-3); border-top: 1px solid var(--rule); text-align: center; }
footer p { margin: 0 0 2px; }
.updated { color: var(--muted); font-size: 13px; }

/* ---------- Narrow screens (single breakpoint) ---------- */
@media (max-width: 600px) {
  :root { --fs-body: 16px; --fs-h1: 26px; --portrait: 140px; }
  main { padding-top: 32px; }
  .intro { flex-direction: column; align-items: stretch; gap: var(--space-2); }
  .intro-side { display: contents; }
  .intro-side .portrait { order: -1; align-self: center; margin-bottom: var(--space-3); }
  .intro-text { order: 0; }
  .intro-side .links, .intro-side .contact { order: 1; text-align: center; }
  .intro-side .links { margin-top: var(--space-2); }
  h1 span[lang="zh-CN"] { display: block; margin-left: -0.5em; }   /* 「 carries a blank left half; pull it back to the margin */
  .focus { grid-template-columns: 1fr; gap: 0; }
  .focus dd { margin-bottom: var(--space-2); }
  .entry { flex-direction: column; gap: var(--space-2); }
  .thumb { flex-basis: auto; }
  .lab .thumb:empty { display: none; }
  .thumb img { width: 50%; }
  .lab .entry { padding-left: var(--space-3); }
  .honors li { flex-direction: column; gap: 0; margin-bottom: var(--space-2); }
}

/* ---------- Reduced motion ---------- */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}