/* ============================================================
   Nam Cao — academic homepage (simple / clean)
   Single column, Source Sans 3, calm blue links, light + dark.
   ============================================================ */

:root {
  --font: "Source Sans 3", system-ui, -apple-system, "Segoe UI", sans-serif;
  --maxw: 1160px;
}

:root[data-theme="light"] {
  --bg:        #ffffff;   /* white */
  --text:      #2f333a;
  --heading:   #1a1d23;
  --title:     #1c3d6e;   /* dark blue section titles */
  --muted:     #6b7280;
  --link:      #2f6db5;   /* blue */
  --link-hover:#1f4e85;
  --border:    #e6e8ec;
  --chip-bg:   #eef2f8;
  --bar:       #d4e2fb;   /* light-blue user bar (bluer) */
  --bar-border:#bdd3f2;
}

:root[data-theme="dark"] {
  --bg:        #1b1e24;
  --text:      #c8ccd2;
  --heading:   #eef1f4;
  --title:     #9fc1ea;   /* light blue section titles (dark mode) */
  --muted:     #9499a1;
  --link:      #6aa6e6;   /* light blue */
  --link-hover:#9cc4f0;
  --border:    #2e333b;
  --chip-bg:   #242931;
  --bar:       #232a35;   /* subtly distinct bar */
  --bar-border:#313845;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; font-size: 18px; }
@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } }

body {
  margin: 0;
  font-family: var(--font);
  font-size: 18px;
  line-height: 1.65;
  color: var(--text);
  background: var(--bg);
  -webkit-font-smoothing: antialiased;
  transition: background-color .25s ease, color .25s ease;
}

img { max-width: 100%; display: block; }
a { color: var(--link); text-decoration: none; }
a:hover { color: var(--link-hover); text-decoration: underline; }
strong { color: var(--heading); font-weight: 600; }
::selection { background: color-mix(in srgb, var(--link) 22%, transparent); }

.skip-link {
  position: absolute; left: -999px; top: 0; z-index: 100;
  background: var(--link); color: #fff; padding: .5em 1em; border-radius: 0 0 6px 0;
}
.skip-link:focus { left: 0; }

/* ---------- Nav ---------- */
.nav {
  position: sticky; top: 0; z-index: 50;
  background: color-mix(in srgb, var(--bar) 92%, transparent);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--bar-border);
}
.nav__inner {
  max-width: var(--maxw); margin: 0 auto;
  display: flex; align-items: center; gap: 1rem;
  padding: 0 1.25rem; height: 54px;
}
.nav__brand { font-weight: 700; color: var(--heading); margin-right: auto; }
.nav__brand:hover { text-decoration: none; color: var(--link); }
.nav__links { display: flex; gap: 1.25rem; }
.nav__links a {
  color: var(--muted); font-size: .95rem; font-weight: 500;
}
.nav__links a:hover, .nav__links a.is-active { color: var(--link); text-decoration: none; }

.theme-toggle {
  display: grid; place-items: center; width: 34px; height: 34px;
  border: 1px solid var(--border); border-radius: 8px;
  background: transparent; color: var(--muted); cursor: pointer;
  transition: color .2s ease, border-color .2s ease;
}
.theme-toggle:hover { color: var(--link); border-color: var(--link); }
.theme-toggle svg { width: 17px; height: 17px; }
.ic-sun  { fill: none; stroke: currentColor; stroke-width: 1.8; stroke-linecap: round; }
.ic-moon { fill: currentColor; }
:root[data-theme="light"] .ic-moon { display: none; }
:root[data-theme="dark"]  .ic-sun  { display: none; }

/* ---------- Layout ---------- */
main { max-width: var(--maxw); margin: 0 auto; padding: 0 1.25rem; }

/* ---------- About ---------- */
.about {
  display: grid;
  grid-template-columns: 200px 1fr;
  gap: 2.4rem;
  align-items: start;
  padding: 3rem 0 2.4rem;
}
.about__card { text-align: center; }
.avatar {
  width: 170px; height: 170px; border-radius: 50%;
  object-fit: cover; margin: 0 auto .9rem;
  border: 1px solid var(--border);
}
.about__name { font-size: 1.45rem; font-weight: 700; color: var(--heading); margin: 0 0 .15rem; }
.about__role { margin: 0; color: var(--text); font-weight: 600; }
.about__org  { margin: .1rem 0 .9rem; color: var(--muted); font-size: .95rem; }
.about__icons { display: flex; justify-content: center; gap: .9rem; }
.about__icons a { color: var(--muted); display: grid; place-items: center; }
.about__icons a:hover { color: var(--link); }
.about__icons svg {
  width: 21px; height: 21px;
  fill: none; stroke: currentColor; stroke-width: 1.7; stroke-linecap: round; stroke-linejoin: round;
}
.about__bio { padding-top: .2rem; }
.about__bio p { margin: 0 0 1rem; }
.about__bio p:last-child { margin-bottom: 0; }

/* ---------- Sections ---------- */
.section { padding: 1.6rem 0; }
.section__title {
  font-size: 1.4rem; font-weight: 700; color: var(--title);
  margin: 0 0 1.1rem; padding-bottom: .4rem;
  border-bottom: 2px solid var(--border);
}
.section__note { margin: -.6rem 0 1rem; color: var(--muted); font-size: .88rem; }

/* ---------- News ---------- */
.news { list-style: none; margin: 0; padding: 0; }
.news li {
  display: grid; grid-template-columns: 6.5rem 1fr; gap: 1rem;
  padding: .35rem 0;
}
.news__date { color: var(--muted); font-size: .92rem; font-variant-numeric: tabular-nums; }
.news__text { color: var(--text); }

/* ---------- Publications ---------- */
.pub-year { font-size: 1.05rem; font-weight: 700; color: var(--muted); margin: 0 0 1rem; }
.pubs { list-style: none; margin: 0; padding: 0; }
.pub {
  display: grid;
  grid-template-columns: 280px 1fr;
  gap: 1.6rem;
  align-items: center;
  padding: 1rem 0 1.2rem;
}
.pub + .pub { border-top: 1px solid var(--border); padding-top: 1.2rem; }
.pub__thumb { margin: 0; }
.pub__thumb img {
  width: 100%; height: auto;   /* whole figure, natural ratio */
  border-radius: 7px; border: 1px solid var(--border); background: #fff;
}
.zoom { display: block; cursor: zoom-in; }
.zoom img { transition: opacity .2s ease; }
.zoom:hover img { opacity: .92; }
.pub__title { font-size: 1.08rem; font-weight: 600; color: var(--heading); margin: 0 0 .25rem; line-height: 1.35; }
.pub__authors { margin: 0 0 .15rem; color: var(--text); font-size: .96rem; }
.pub__authors .me { color: var(--heading); font-weight: 700; text-decoration: underline; text-underline-offset: 2px; }
.pub__authors sup { color: var(--link); }
.pub__venue { margin: 0 0 .5rem; color: var(--muted); font-size: .94rem; }
.pub__badge {
  display: inline-block; font-size: .72rem; font-weight: 700; letter-spacing: .04em;
  text-transform: uppercase; color: #d35f4e; vertical-align: middle;
  padding: .1em .5em; border: 1px solid currentColor; border-radius: 4px;
}
:root[data-theme="dark"] .pub__badge { color: #ef8a7c; }
.pub__links { margin: 0; display: flex; gap: .5rem; flex-wrap: wrap; }
.pub__links a {
  font-size: .85rem; font-weight: 600;
  padding: .18em .7em; border: 1px solid var(--border); border-radius: 5px;
  background: var(--chip-bg); color: var(--link);
}
.pub__links a:hover { border-color: var(--link); text-decoration: none; }

/* ---------- Experience / Education ---------- */
.entries { list-style: none; margin: 0; padding: 0; }
.entry { padding: .5rem 0 1rem; }
.entry + .entry { border-top: 1px solid var(--border); padding-top: 1rem; }
.entry__head {
  display: flex; justify-content: space-between; align-items: baseline;
  gap: 1rem; flex-wrap: wrap;
}
.entry__role { font-weight: 700; color: var(--heading); font-size: 1.05rem; }
.entry__date { color: var(--muted); font-size: .9rem; white-space: nowrap; font-variant-numeric: tabular-nums; }
.entry__org  { margin: .1rem 0 .5rem; color: var(--text); }
.entry__note { margin: 0; color: var(--muted); }
.entry__desc { margin: .35rem 0 0; color: var(--muted); font-size: .96rem; }
.role-highlight { color: #d35f4e; font-weight: 700; }   /* soft red */
:root[data-theme="dark"] .role-highlight { color: #ef8a7c; }
.entry__points { margin: .4rem 0 0; padding-left: 1.15rem; }
.entry__points li { margin: 0 0 .4rem; }
.entry__points li::marker { color: var(--muted); }

/* ---------- Research projects (gallery) ---------- */
.gallery { list-style: none; margin: 0; padding: 0; }
.project {
  display: grid;
  grid-template-columns: 280px 1fr;
  gap: 1.6rem;
  align-items: center;
  padding: .6rem 0 1.1rem;
}
.project + .project { border-top: 1px solid var(--border); padding-top: 1.1rem; }
.project__info .entry__points { margin-top: .4rem; }
.project__info .entry__points li { margin-bottom: 0; }
.project__media { margin: 0; order: -1; }   /* image panel on the left */
.project__media img {
  width: 100%;
  height: auto;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: #fff;
}

/* ---------- Education (compact, one line per degree) ---------- */
.edu { list-style: none; margin: 0; padding: 0; }
.edu__item {
  display: flex; justify-content: space-between; align-items: baseline;
  gap: 1.4rem; padding: .45rem 0;
}
.edu__text { color: var(--text); }
.edu__text strong { color: var(--heading); font-weight: 700; }
.edu__date {
  color: var(--muted); white-space: nowrap;
  font-size: .92rem; font-variant-numeric: tabular-nums;
}

/* ---------- Awards ---------- */
.awards { margin: 0; padding-left: 1.15rem; }
.awards li { margin: 0 0 .55rem; }
.awards li::marker { color: var(--muted); }
.awards__year { color: var(--muted); white-space: nowrap; }

/* ---------- Footer ---------- */
.footer {
  max-width: var(--maxw); margin: 1.5rem auto 0; padding: 1.6rem 1.25rem 2.4rem;
  border-top: 1px solid var(--border);
  color: var(--muted); font-size: .9rem;
  display: flex; justify-content: space-between; flex-wrap: wrap; gap: .4rem;
}
.footer p { margin: 0; }

/* ---------- Lightbox ---------- */
.lightbox {
  position: fixed; inset: 0; z-index: 200;
  display: flex; align-items: center; justify-content: center;
  padding: 4vmin;
  background: rgba(15, 18, 24, .84);
  -webkit-backdrop-filter: blur(4px); backdrop-filter: blur(4px);
}
.lightbox[hidden] { display: none; }
.lightbox__img {
  max-width: 94vw; max-height: 90vh;
  border-radius: 8px; background: #fff;
  box-shadow: 0 24px 70px rgba(0, 0, 0, .55);
}
.lightbox__close {
  position: absolute; top: 3vmin; right: 4vmin;
  width: 42px; height: 42px; border-radius: 50%;
  border: none; cursor: pointer; line-height: 1; font-size: 1.5rem;
  background: rgba(255, 255, 255, .15); color: #fff;
  transition: background-color .2s ease;
}
.lightbox__close:hover { background: rgba(255, 255, 255, .28); }

/* ---------- Responsive ---------- */
@media (max-width: 640px) {
  .nav__links { display: none; }
  .about {
    grid-template-columns: 1fr; gap: 1.4rem; text-align: center;
    padding-top: 2.2rem;
  }
  .about__bio { text-align: left; }
  .news li { grid-template-columns: 1fr; gap: .1rem; padding: .5rem 0; }
  .news__date { font-size: .85rem; }
  .entry__head { gap: .2rem; }
  .edu__item { flex-direction: column; gap: .1rem; }
  .project { grid-template-columns: 1fr; gap: 1rem; }
  .project__media { max-width: 320px; }
  .pub { grid-template-columns: 1fr; gap: .9rem; }
  .pub__thumb { max-width: 320px; }
}