/* Yuda Bi — homepage
   A single white column set in Times New Roman; the research directions,
   the paper list and each paper sit in framed cards. Formulas are typeset
   with LaTeX (newtx, a Times math) by scripts/build_math.sh and served as SVG. */

:root {
  --ink: #111;
  --text: #1a1a1a;
  --muted: #3f3f3f;
  --faint: #6b6b6b;
  --rule: #d9d9d9;
  --frame: #d2d9e3;      /* card borders */
  --frame-soft: #e4e8ee; /* lines and panels inside a card */
  --head: #f4f6f9;       /* card header, hover */
  --panel: #fafbfc;      /* formula panel */
  --accent: #1f4e8c;
  --link: #1f4e8c;
  --shadow: 0 1px 2px rgba(16, 32, 64, 0.04), 0 8px 20px -18px rgba(16, 32, 64, 0.28);
  --measure: 40rem;   /* ~78 characters per line in Times at 17px */
}

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

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

body {
  margin: 0;
  background: #fff;
  color: var(--text);
  font-family: "Times New Roman", Times, "Liberation Serif", "Nimbus Roman",
    "TeX Gyre Termes", serif;
  font-size: 1.0625rem;   /* 17px */
  line-height: 1.58;
  font-kerning: normal;
  text-rendering: optimizeLegibility;
}

@media (prefers-reduced-motion: no-preference) {
  html { scroll-behavior: smooth; }
}

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

p { margin: 0 0 0.85em; }
p, li { text-wrap: pretty; }
h1, h2, h3, .dir-title { text-wrap: balance; }

strong, b { font-weight: 700; color: var(--ink); }

a { color: var(--link); text-decoration: none; }
a:hover { text-decoration: underline; text-underline-offset: 0.15em; }
a:focus-visible, summary:focus-visible { outline: 2px solid var(--link); outline-offset: 2px; }

/* Inline mathematics written in HTML */
var { font-style: italic; }
sub, sup { font-size: 0.75em; line-height: 0; position: relative; vertical-align: baseline; }
sup { top: -0.45em; }
sub { top: 0.25em; }
.ss {                     /* stacked sub- and superscript, e.g. w_j^4 */
  display: inline-block;
  vertical-align: -0.34em;
  font-size: 0.75em;
  line-height: 1;
  margin-left: 0.04em;
}
.ss > sup, .ss > sub { display: block; font-size: 1em; position: static; line-height: 1; }
.nowrap { white-space: nowrap; }

/* Small capital labels */
.label, .toc-group, .display-label, .paper h4, .dir-num {
  font-size: 0.8125rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--accent);
}

/* Status tags */
.tag {
  display: inline-block;
  padding: 0.06rem 0.55rem 0.04rem;
  border: 1px solid var(--frame);
  border-radius: 999px;
  background: #fff;
  font-size: 0.75rem;
  line-height: 1.45;
  letter-spacing: 0.02em;
  color: var(--muted);
  white-space: nowrap;
}
.tag-pub { background: var(--accent); border-color: var(--accent); color: #fff; }

/* ---------- Page ---------- */

.page {
  max-width: calc(var(--measure) + 3rem);
  margin: 0 auto;
  padding: 3.75rem 1.5rem 3rem;
}

/* ---------- Header ---------- */

.intro {
  display: flex;
  align-items: center;
  gap: 1.75rem;
}
.portrait {
  flex: none;
  width: 7.5rem;
  height: 7.5rem;
  border-radius: 50%;
  object-fit: cover;
  object-position: 50% 30%;
  border: 1px solid var(--frame-soft);
  box-shadow: 0 6px 16px -10px rgba(16, 32, 64, 0.4);
}
.intro-text { min-width: 0; }
h1 {
  font-size: 2.25rem;
  font-weight: 700;
  line-height: 1.1;
  letter-spacing: 0.005em;
  color: var(--ink);
  margin: 0 0 0.35rem;
}
.affil { color: var(--muted); margin: 0; }
.links {
  list-style: none;
  margin: 0.8rem 0 0;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
}
.links a {
  display: inline-block;
  padding: 0.14rem 0.75rem 0.1rem;
  border: 1px solid var(--frame);
  border-radius: 999px;
  font-size: 0.9375rem;
  white-space: nowrap;
  transition: background-color 120ms ease, border-color 120ms ease;
}
.links a:hover { text-decoration: none; background: var(--head); border-color: var(--accent); }

/* Epigraph under the name */
.motto {
  margin: 1.9rem 0 0;
  padding-left: 1.15rem;
  border-left: 2px solid var(--accent);
  max-width: 34rem;
}
.motto p {
  margin: 0;
  font-size: 1.125rem;
  font-style: italic;
  line-height: 1.5;
  color: var(--muted);
  text-wrap: pretty;
}
.motto cite {
  display: block;
  margin-top: 0.55rem;
  font-size: 0.75rem;
  font-style: normal;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--accent);
}

.bio { margin: 1.5rem 0 0; }

/* Research directions */
.directions {
  list-style: none;
  margin: 1rem 0 0;
  padding: 0;
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.9rem;
}
.directions li {
  padding: 0.85rem 0.95rem 1rem;
  border: 1px solid var(--frame);
  border-top: 3px solid var(--accent);
  border-radius: 6px;
  background: linear-gradient(#fff, var(--panel));
  box-shadow: var(--shadow);
}
.dir-num { display: block; }
.dir-title {
  display: block;
  margin: 0.2rem 0 0.4rem;
  font-size: 1.0625rem;
  line-height: 1.3;
}
.directions p { margin: 0; font-size: 0.9rem; line-height: 1.5; color: var(--muted); }

/* ---------- Sections ---------- */

h2 {
  position: relative;
  font-size: 1.3125rem;
  font-weight: 700;
  line-height: 1.3;
  color: var(--ink);
  margin: 2.9rem 0 1.15rem;
  padding-bottom: 0.45rem;
  border-bottom: 1px solid var(--rule);
  scroll-margin-top: 1.5rem;
}
h2::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: -2px;
  width: 3.25rem;
  height: 3px;
  background: var(--accent);
}

/* Paper list */
.toc-card {
  padding: 0.35rem 0 0.45rem;
  border: 1px solid var(--frame);
  border-radius: 6px;
  background: #fff;
  box-shadow: var(--shadow);
}
.toc-group { margin: 0.75rem 1.25rem 0.35rem; }
.toc { list-style: none; margin: 0; padding: 0; }
.toc a {
  display: grid;
  grid-template-columns: 1.5rem minmax(0, 1fr) auto;
  column-gap: 0.6rem;
  align-items: baseline;
  padding: 0.5rem 1.25rem;
  border-top: 1px solid var(--frame-soft);
  color: var(--text);
  transition: background-color 120ms ease;
}
.toc a:hover { text-decoration: none; background: var(--head); }
.toc a:hover .toc-title { color: var(--link); text-decoration: underline; text-underline-offset: 0.15em; }
.toc-num { color: var(--accent); font-weight: 700; }
.toc-title { color: var(--ink); }
.toc .tag { align-self: center; }

/* ---------- Papers: framed cards ---------- */

.paper {
  margin-top: 1.5rem;
  background: #fff;
  border: 1px solid var(--frame);
  border-top: 3px solid var(--accent);
  border-radius: 6px;
  box-shadow: var(--shadow);
  overflow: hidden;
  scroll-margin-top: 1.5rem;
}
h2 + .paper { margin-top: 1.25rem; }
.paper:target {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px rgba(31, 78, 140, 0.12), var(--shadow);
}

.paper-head {
  background: var(--head);
  border-bottom: 1px solid var(--frame);
  padding: 1.15rem 1.5rem 1.05rem;
}
.paper-body { padding: 0.25rem 1.5rem 1.25rem; }

.paper h3 {
  display: flex;
  align-items: baseline;
  gap: 0.65rem;
  font-size: 1.3125rem;
  font-weight: 700;
  line-height: 1.3;
  color: var(--ink);
  margin: 0 0 0.5rem;
}
.paper h3 .num {
  flex: none;
  display: inline-grid;
  place-items: center;
  width: 1.7rem;
  height: 1.7rem;
  border-radius: 50%;
  background: var(--accent);
  color: #fff;
  font-size: 0.9375rem;
}
.byline { margin-bottom: 0.2rem; }
.byline .me { font-weight: 700; color: var(--ink); }
.venue-line { color: var(--muted); margin-bottom: 0; }
.venue-line .tag { margin-right: 0.45rem; position: relative; top: -0.08em; }
.venue-line a:not(:last-child)::after {
  content: "\00b7";
  color: var(--faint);
  display: inline-block;
  padding: 0 0.45em;
}
.note { color: var(--muted); font-size: 0.9375rem; margin: 0.15rem 0 0; }

/* Displayed formulas, on a light panel */
.display {
  margin: 1.25rem 0 0.4rem;
  padding: 0.95rem 1.25rem 1.05rem;
  background: var(--panel);
  border: 1px solid var(--frame-soft);
  border-radius: 4px;
}
.display-label {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.75rem;
  margin: 0 0 0.85rem;
  font-size: 0.75rem;
  letter-spacing: 0.14em;
}
.display-label::before, .display-label::after {
  content: "";
  width: 2.25rem;
  border-top: 1px solid var(--frame);
}
.display picture, .display > img { display: block; }
.display img { margin: 0 auto; }
.display .gloss {
  max-width: 38rem;
  margin: 0.75rem auto 0;
  text-align: center;
  font-size: 0.9688rem;
  color: var(--muted);
}
.display .gloss + picture,
.display .gloss + img { margin-top: 1.2rem; padding-top: 1.1rem; border-top: 1px solid var(--frame-soft); }

.paper h4 {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  line-height: 1.3;
  margin: 1.6rem 0 0.6rem;
}
.paper h4::after { content: ""; flex: 1; border-top: 1px solid var(--frame-soft); }

.results { margin: 0; padding-left: 1.2rem; list-style: square; }
.results li::marker { color: var(--accent); }
.results li + li { margin-top: 0.65rem; }
.thm-name { font-style: italic; }

/* Tables */
details.table { margin: 1.1rem 0 0; }
details.table > summary { cursor: pointer; color: var(--link); width: fit-content; }
details.table[open] > summary { margin-bottom: 0.8rem; }
.table-scroll { overflow-x: auto; -webkit-overflow-scrolling: touch; }
table {
  border-collapse: collapse;
  font-size: 0.9375rem;
  line-height: 1.35;
  font-variant-numeric: tabular-nums;
  min-width: 100%;
  border-top: 1px solid var(--ink);
  border-bottom: 1px solid var(--ink);
}
th, td { padding: 0.32rem 0.75rem 0.32rem 0; text-align: right; white-space: nowrap; vertical-align: baseline; }
th:first-child, td:first-child { text-align: left; }
th:last-child, td:last-child { padding-right: 0; }
thead th { font-weight: 400; font-style: italic; border-bottom: 1px solid var(--ink); vertical-align: bottom; }
thead th.group { text-align: center; border-bottom: 1px solid var(--rule); }
tbody th { font-weight: 400; }
td .pred { color: var(--muted); }
td sup { font-size: 0.7em; }
.table-note { color: var(--muted); font-size: 0.9375rem; margin-top: 0.6rem; }

/* Figures: bled to the edges of the card so the panels keep their width */
.figure {
  margin: 1.5rem -1.5rem 0;
  padding: 0.9rem 0.9rem 0.8rem;
  border-top: 1px solid var(--frame-soft);
  border-bottom: 1px solid var(--frame-soft);
  border-left: 0;
  border-right: 0;
  border-radius: 0;
}
.fig-scroll { overflow-x: auto; -webkit-overflow-scrolling: touch; }
.fig-scroll a { display: block; }
.figure figcaption { margin-top: 0.7rem; font-size: 0.9375rem; color: var(--muted); }
.swipe-hint { display: none; }

.to-top { margin: 1rem 0 0; text-align: right; font-size: 0.875rem; }
.to-top a { color: var(--faint); }
.to-top a:hover { color: var(--link); }

/* ---------- Footer ---------- */

.site-footer {
  margin-top: 3.25rem;
  padding-top: 1.1rem;
  border-top: 1px solid var(--rule);
  color: var(--faint);
  font-size: 0.9375rem;
  text-align: center;
}
.site-footer p { margin: 0; }
[hidden] { display: none !important; }

/* Visitor count (GoatCounter, filled in on load) */
.visit { margin-top: 0.35rem; }
.visit .count {
  color: var(--muted);
  font-variant-numeric: tabular-nums;
}

/* ---------- Small screens ---------- */

@media (max-width: 720px) {
  .directions { grid-template-columns: minmax(0, 1fr); gap: 0.7rem; }
}

@media (max-width: 640px) {
  body { font-size: 1rem; }
  .page { padding: 2rem 1rem 2.5rem; }
  .intro { gap: 1rem; align-items: flex-start; }
  .portrait { width: 5.25rem; height: 5.25rem; }
  h1 { font-size: 1.75rem; }
  .links { gap: 0.35rem; margin-top: 0.65rem; }
  .links a { font-size: 0.875rem; padding: 0.1rem 0.6rem 0.06rem; }
  .bio { margin-top: 1.5rem; }
  .toc-group { margin-inline: 1rem; }
  .toc a { grid-template-columns: 1.3rem minmax(0, 1fr); padding: 0.5rem 1rem; }
  .toc .tag { grid-column: 2; justify-self: start; margin-top: 0.3rem; }
  .paper-head { padding: 0.95rem 1rem 0.9rem; }
  .paper-body { padding: 0.1rem 1rem 1rem; }
  .paper h3 { font-size: 1.125rem; gap: 0.5rem; }
  .paper h3 .num { width: 1.45rem; height: 1.45rem; font-size: 0.8125rem; }
  .display { padding: 0.85rem 0.6rem 0.9rem; }
  .figure { margin-inline: -1rem; padding: 0.6rem; }
  .fig-scroll img { width: 40rem; max-width: none; }
  .swipe-hint { display: block; font-size: 0.875rem; color: var(--faint); margin: 0.3rem 0 0; }
}

@media print {
  .paper, .toc-card, .directions li { box-shadow: none; }
  .paper { break-inside: avoid-page; }
  .to-top, .swipe-hint, .visit { display: none !important; }
  .fig-scroll img { width: 100% !important; }
  a { color: inherit; }
}