/* ===========================================================================
   Qingsong Pan academic homepage
   Direction: refined editorial CV, quiet research-first hierarchy.
   =========================================================================== */

:root {
  --paper: #faf8f2;
  --paper-warm: #f3efe5;
  --surface: #fffdf8;
  --surface-muted: #f6f1e8;
  --ink: #171713;
  --ink-soft: #57534b;
  --ink-muted: #7a7468;
  --rule: #dfd7c9;
  --rule-strong: #c9bda9;
  --accent: #234f65;
  --accent-deep: #153747;
  --accent-warm: #8a4034;
  --accent-olive: #596744;
  --shadow: 0 18px 44px rgba(50, 43, 31, 0.08);
  --maxw: 940px;
  --contentw: 760px;
  --gap: clamp(3rem, 7vw, 5rem);
  --pad: clamp(1.25rem, 5vw, 2.25rem);
}

* { box-sizing: border-box; }

html {
  scroll-behavior: smooth;
  scroll-padding-top: 5rem;
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
  }
}

body {
  margin: 0;
  overflow-x: hidden;
  background:
    linear-gradient(180deg, rgba(255, 255, 255, 0.68), rgba(255, 255, 255, 0) 15rem),
    linear-gradient(90deg, rgba(35, 79, 101, 0.035) 1px, transparent 1px),
    var(--paper);
  background-size: auto, 72px 72px, auto;
  color: var(--ink);
  font-family: "IBM Plex Sans", "Segoe UI", system-ui, sans-serif;
  font-size: 17px;
  line-height: 1.65;
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
}

body::selection {
  background: rgba(35, 79, 101, 0.16);
}

a {
  color: var(--accent-deep);
  text-decoration: underline;
  text-decoration-color: rgba(35, 79, 101, 0.24);
  text-decoration-thickness: 1px;
  text-underline-offset: 0.18em;
  transition: color 160ms ease, text-decoration-color 160ms ease;
}

a:hover {
  color: var(--accent);
  text-decoration-color: currentColor;
}

a:focus-visible,
summary:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 4px;
  border-radius: 4px;
}

/* Top bar */
.topbar {
  position: sticky;
  top: 0;
  z-index: 10;
  display: grid;
  grid-template-columns: minmax(10rem, 1fr) auto;
  align-items: center;
  gap: 1rem;
  padding: 0.86rem max(var(--pad), calc((100vw - var(--maxw)) / 2 + var(--pad)));
  background: rgba(250, 248, 242, 0.9);
  border-bottom: 1px solid rgba(201, 189, 169, 0.72);
  backdrop-filter: blur(14px);
  box-shadow: 0 1px 0 rgba(255, 255, 255, 0.72) inset;
}

.topbar__name {
  color: var(--ink);
  font-family: "Newsreader", Georgia, serif;
  font-size: 1.22rem;
  font-weight: 500;
  letter-spacing: 0;
  text-decoration: none;
}

.topbar__nav {
  display: flex;
  flex-wrap: wrap;
  justify-content: flex-end;
  gap: 0.28rem 0.42rem;
}

.topbar__nav a {
  padding: 0.32rem 0.48rem;
  color: var(--ink-soft);
  border-radius: 5px;
  font-family: "IBM Plex Mono", Consolas, monospace;
  font-size: 0.72rem;
  letter-spacing: 0.04em;
  text-decoration: none;
  text-transform: uppercase;
}

.topbar__nav a:hover {
  background: rgba(35, 79, 101, 0.07);
  color: var(--accent-deep);
}

/* Layout */
main {
  width: min(100%, var(--maxw));
  min-width: 0;
  margin: 0 auto;
  padding: 0 var(--pad);
}

.section {
  width: min(100%, var(--contentw));
  min-width: 0;
  margin: 0 auto;
  padding-top: var(--gap);
}

/* About */
.about {
  position: relative;
  display: grid;
  grid-template-columns: 176px minmax(0, 1fr);
  gap: clamp(1.5rem, 5vw, 3rem);
  align-items: start;
  padding: clamp(3.5rem, 8vw, 5.5rem) 0 clamp(2.5rem, 6vw, 4rem);
  border-bottom: 1px solid var(--rule);
}

.about::after {
  content: "";
  position: absolute;
  right: 0;
  bottom: -1px;
  width: min(54%, 420px);
  height: 2px;
  background: linear-gradient(90deg, transparent, var(--accent), var(--accent-warm));
}

.portrait {
  width: 176px;
  height: 176px;
  border: 1px solid rgba(201, 189, 169, 0.9);
  border-radius: 6px;
  background: #ebe6da center / cover no-repeat;
  background-image: url("photo.jpg");
  box-shadow: var(--shadow);
  overflow: hidden;
  position: relative;
}

.portrait::after {
  content: "";
  position: absolute;
  inset: 0;
  border: 1px solid rgba(255, 255, 255, 0.58);
  border-radius: inherit;
  pointer-events: none;
}

.about__body {
  min-width: 0;
  max-width: 680px;
}

.about__name {
  margin: 0 0 0.42rem;
  font-family: "Newsreader", Georgia, serif;
  font-size: clamp(2.35rem, 6vw, 3.5rem);
  font-weight: 500;
  letter-spacing: 0;
  line-height: 0.98;
  overflow-wrap: anywhere;
}

.about__name span[lang="zh"] {
  color: var(--ink-soft);
  font-weight: 400;
  white-space: nowrap;
}

.about__role {
  margin: 0 0 1.25rem;
  color: var(--accent-deep);
  font-size: 1.02rem;
  font-weight: 500;
}

.about__bio {
  margin: 0 0 1.6rem;
  max-width: 62ch;
  color: var(--ink-soft);
  font-size: 1.03rem;
  overflow-wrap: anywhere;
}

.links {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0;
  list-style: none;
  margin: 0;
  padding: 0;
  border-top: 1px solid var(--rule);
  border-bottom: 1px solid var(--rule);
}

.links li {
  min-width: 0;
  padding: 0.78rem 0.95rem;
  border-right: 1px solid var(--rule);
}

.links li:first-child {
  padding-left: 0;
}

.links li:last-child {
  border-right: 0;
}

.links a {
  display: inline-block;
  max-width: 100%;
  overflow-wrap: anywhere;
  font-size: 0.95rem;
  font-weight: 500;
}

.links__key {
  display: block;
  margin-bottom: 0.12rem;
  color: var(--ink-muted);
  font-family: "IBM Plex Mono", Consolas, monospace;
  font-size: 0.66rem;
  font-weight: 500;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

/* Section headings */
.section__title {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 1rem;
  align-items: baseline;
  margin: 0 0 1.55rem;
  color: var(--ink);
  font-family: "Newsreader", Georgia, serif;
  font-size: clamp(1.75rem, 4vw, 2.2rem);
  font-weight: 500;
  letter-spacing: 0;
  line-height: 1.05;
}

.section__title::after {
  content: "";
  height: 1px;
  background: linear-gradient(90deg, var(--rule-strong), transparent);
}

.group {
  margin: 2.2rem 0 0.95rem;
  color: var(--ink-muted);
  font-family: "IBM Plex Mono", Consolas, monospace;
  font-size: 0.72rem;
  font-weight: 500;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.section__title + .group {
  margin-top: 0;
}

/* Papers */
.papers {
  display: grid;
  gap: 1rem;
  list-style: none;
  margin: 0;
  padding: 0;
  counter-reset: paper;
}

.paper {
  position: relative;
  min-width: 0;
  max-width: 100%;
  counter-increment: paper;
  padding: 1.18rem 1.22rem 1.12rem 3.65rem;
  border: 1px solid rgba(223, 215, 201, 0.9);
  border-left: 3px solid rgba(35, 79, 101, 0.62);
  border-radius: 8px;
  background: rgba(255, 253, 248, 0.72);
  box-shadow: 0 1px 0 rgba(255, 255, 255, 0.75) inset;
}

.paper::before {
  content: counter(paper, decimal-leading-zero);
  position: absolute;
  top: 1.24rem;
  left: 1.08rem;
  color: var(--ink-muted);
  font-family: "IBM Plex Mono", Consolas, monospace;
  font-size: 0.72rem;
  letter-spacing: 0.04em;
}

.paper__title {
  margin: 0;
  font-family: "Newsreader", Georgia, serif;
  font-size: 1.24rem;
  font-weight: 500;
  line-height: 1.28;
  overflow-wrap: anywhere;
}

.paper__title a {
  color: var(--ink);
  text-decoration-color: rgba(35, 79, 101, 0.28);
  overflow-wrap: anywhere;
}

.paper__title a:hover {
  color: var(--accent-deep);
}

.paper__byline {
  margin: 0.42rem 0 0;
  color: var(--ink-soft);
  font-size: 0.96rem;
}

.paper__meta {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
  margin: 0.62rem 0 0;
}

.tag {
  display: inline-flex;
  align-items: center;
  min-height: 1.54rem;
  padding: 0.16rem 0.48rem;
  border: 1px solid rgba(201, 189, 169, 0.9);
  border-radius: 4px;
  background: var(--surface-muted);
  color: var(--ink-soft);
  font-family: "IBM Plex Mono", Consolas, monospace;
  font-size: 0.68rem;
  letter-spacing: 0.03em;
  line-height: 1.2;
}

.tag--rr {
  border-color: rgba(138, 64, 52, 0.28);
  background: rgba(138, 64, 52, 0.08);
  color: var(--accent-warm);
}

.paper__abstract {
  margin: 0.72rem 0 0;
}

.paper__abstract summary,
.section-details > summary {
  cursor: pointer;
  width: fit-content;
  color: var(--accent-deep);
  font-family: "IBM Plex Mono", Consolas, monospace;
  font-size: 0.68rem;
  font-weight: 500;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.paper__abstract summary:hover,
.section-details > summary:hover {
  color: var(--accent);
}

.paper__abstract p {
  margin: 0.68rem 0 0;
  padding-top: 0.72rem;
  border-top: 1px solid rgba(223, 215, 201, 0.8);
  color: var(--ink-soft);
  font-size: 0.95rem;
  line-height: 1.72;
}

/* Service and presentations */
.service-list {
  display: grid;
  gap: 0.6rem;
  list-style: none;
  margin: 0;
  padding: 0;
}

.service-list li {
  padding: 0.72rem 0.95rem;
  border-left: 3px solid var(--accent-olive);
  background: rgba(255, 253, 248, 0.62);
  color: var(--ink-soft);
  font-weight: 500;
}

.presentation-list {
  margin: 0;
  padding: 0 0 0 1rem;
  border-left: 2px solid rgba(35, 79, 101, 0.35);
  color: var(--ink-soft);
  font-size: 0.98rem;
  line-height: 1.78;
}

.presentation-list + .group {
  margin-top: 2.2rem;
}

/* Teaching */
.section-details {
  margin: 0;
  padding: 1.1rem 0 0;
  border-top: 1px solid var(--rule);
}

.section-details[open] > summary {
  margin-bottom: 1.4rem;
}

.section-details .group:first-of-type {
  margin-top: 0;
}

.teaching {
  display: grid;
  gap: 0.58rem;
  list-style: none;
  margin: 0;
  padding: 0;
}

.teaching li {
  display: grid;
  grid-template-columns: 5.8rem minmax(0, 1fr);
  gap: 0.7rem;
  align-items: baseline;
  color: var(--ink-soft);
}

.teaching__role {
  color: var(--ink-muted);
  font-family: "IBM Plex Mono", Consolas, monospace;
  font-size: 0.67rem;
  font-weight: 500;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.teaching__note {
  color: var(--ink-muted);
  font-size: 0.9rem;
}

/* Footer */
.footer {
  width: min(100%, var(--contentw));
  margin: var(--gap) auto 0;
  padding: 1.8rem var(--pad) 3.2rem;
  border-top: 1px solid var(--rule);
  color: var(--ink-muted);
  font-size: 0.88rem;
}

.footer p {
  margin: 0;
}

/* Responsive */
@media (max-width: 760px) {
  .topbar {
    grid-template-columns: 1fr;
    align-items: start;
  }

  .topbar__nav {
    justify-content: flex-start;
  }

  .about {
    grid-template-columns: 140px minmax(0, 1fr);
  }

  .portrait {
    width: 140px;
    height: 140px;
  }

  .links {
    grid-template-columns: 1fr;
  }

  .links li,
  .links li:first-child {
    padding: 0.72rem 0;
    border-right: 0;
    border-bottom: 1px solid var(--rule);
  }

  .links li:last-child {
    border-bottom: 0;
  }
}

@media (max-width: 560px) {
  body {
    font-size: 16px;
    background-size: auto, 56px 56px, auto;
  }

  main,
  .footer {
    width: 100vw;
    max-width: 100vw;
    padding-left: 1.5rem;
    padding-right: 1.5rem;
  }

  .section,
  .about,
  .about__body,
  .links,
  .papers,
  .paper {
    width: calc(100vw - 3rem);
    max-width: calc(100vw - 3rem);
  }

  .topbar {
    position: static;
  }

  .topbar__nav a {
    padding-left: 0;
    padding-right: 0.4rem;
    font-size: 0.68rem;
  }

  .about {
    grid-template-columns: 1fr;
    padding-top: 2.7rem;
  }

  .portrait {
    width: 128px;
    height: 128px;
  }

  .about__name {
    font-size: 2.02rem;
    line-height: 1.06;
  }

  .about__name span[lang="zh"] {
    display: block;
    margin-top: 0.12rem;
    white-space: normal;
  }

  .about__role {
    font-size: 0.98rem;
    overflow-wrap: anywhere;
  }

  .section__title {
    grid-template-columns: 1fr;
    gap: 0.55rem;
  }

  .paper {
    padding: 1rem 1rem 1rem 1.05rem;
  }

  .paper::before {
    position: static;
    display: block;
    margin-bottom: 0.42rem;
  }

  .paper__title {
    font-size: 1.08rem;
  }

  .teaching li {
    grid-template-columns: 1fr;
    gap: 0.1rem;
  }
}