/* =====================================================================
   Yipin Guo — Personal Website
   Warm-white theme · clean, compact typography.
===================================================================== */
:root {
  --bg:        #faf6ef;
  --bg-soft:   #f4eee3;
  --card:      #fffdf8;
  --ink:       #2a2620;
  --ink-soft:  #6f685c;
  --line:      #e7dfd0;
  --accent:    #b5773a;
  --accent-deep:#8a5623;
  --accent-soft:#f0e2cf;
  --shadow:    0 1px 2px rgba(60,45,25,.04), 0 6px 22px rgba(90,65,30,.06);
  --shadow-lg: 0 4px 12px rgba(60,45,25,.06), 0 18px 44px rgba(90,65,30,.09);
  --radius:    14px;
  --maxw:      980px;
  --font-sans: "Inter", system-ui, -apple-system, sans-serif;
  --font-disp: "Fraunces", Georgia, serif;
  --font-mono: "JetBrains Mono", ui-monospace, monospace;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 72px; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font-sans);
  font-size: 15px;
  line-height: 1.58;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}
img { max-width: 100%; display: block; }
a { color: inherit; text-decoration: none; }

.block, .work, .hero, .contact { padding-left: 24px; padding-right: 24px; }

/* ============ NAV ============ */
.nav {
  position: sticky; top: 0; z-index: 50;
  display: flex; align-items: center; justify-content: space-between; gap: 24px;
  padding: 11px clamp(20px, 5vw, 40px);
  background: rgba(250, 246, 239, .85);
  backdrop-filter: saturate(140%) blur(12px);
  border-bottom: 1px solid var(--line);
}
.nav__brand { font-family: var(--font-disp); font-weight: 600; font-size: 1.02rem; }
.nav__links { display: flex; gap: clamp(14px, 2.2vw, 26px); }
.nav__links a {
  font-size: .84rem; color: var(--ink-soft); font-weight: 500;
  position: relative; padding: 3px 0; transition: color .2s;
}
.nav__links a:hover { color: var(--ink); }
.nav__links a.is-active { color: var(--accent-deep); }
.nav__links a.is-active::after {
  content: ""; position: absolute; left: 0; right: 0; bottom: -1px;
  height: 2px; background: var(--accent); border-radius: 2px;
}
@media (max-width: 640px) {
  .nav__links a:not(:first-child):not(:last-child) { display: none; }
}

/* ============ HERO ============ */
.hero {
  max-width: var(--maxw); margin: clamp(34px, 6vw, 64px) auto clamp(30px, 5vw, 52px);
  display: grid; grid-template-columns: 1.4fr .85fr;
  gap: clamp(26px, 5vw, 56px); align-items: center;
}
.hero__eyebrow {
  font-family: var(--font-mono); font-size: .72rem; letter-spacing: 1.4px;
  text-transform: uppercase; color: var(--accent-deep); margin: 0 0 12px;
}
.hero__name {
  font-family: var(--font-disp); font-weight: 600;
  font-size: clamp(2.4rem, 6vw, 3.6rem); line-height: 1; letter-spacing: -.5px;
  margin: 0 0 16px;
}
.hero__tagline {
  font-size: clamp(.98rem, 1.6vw, 1.1rem); color: var(--ink-soft);
  max-width: 42ch; margin: 0 0 20px;
}
.hero__tagline em { font-family: var(--font-disp); font-style: italic; color: var(--accent-deep); }
.hero__interests {
  list-style: none; padding: 0; margin: 0 0 24px;
  display: flex; flex-wrap: wrap; gap: 7px;
}
.hero__interests li {
  font-size: .78rem; font-weight: 500; padding: 5px 12px;
  background: var(--accent-soft); color: var(--accent-deep); border-radius: 999px;
}
.hero__actions { display: flex; flex-wrap: wrap; gap: 12px; }
.hero__contact {
  list-style: none; padding: 0; margin: 22px 0 0;
  display: flex; flex-wrap: wrap; align-items: center; gap: 8px 18px;
  border-top: 1px solid var(--line); padding-top: 18px;
}
.hero__contact li { font-size: .84rem; }
.hero__contact a {
  color: var(--accent-deep); font-weight: 600;
  border-bottom: 1.5px solid transparent; transition: border-color .2s;
}
.hero__contact a:hover { border-color: var(--accent); }
.hero__contact-loc { color: var(--ink-soft); font-family: var(--font-mono); font-size: .76rem; }
.btn {
  font-weight: 600; font-size: .88rem; padding: 10px 20px; border-radius: 999px;
  transition: transform .18s ease, box-shadow .18s ease, background .2s, border-color .2s;
  border: 1.5px solid transparent;
}
.btn--primary { background: var(--accent); color: #fff; box-shadow: var(--shadow); }
.btn--primary:hover { background: var(--accent-deep); transform: translateY(-2px); }
.btn--ghost { border-color: var(--line); color: var(--ink); }
.btn--ghost:hover { border-color: var(--accent); color: var(--accent-deep); transform: translateY(-2px); }
.hero__photo { margin: 0; position: relative; }
.hero__photo img {
  width: 100%; aspect-ratio: 4 / 5; object-fit: cover; object-position: top;
  border-radius: var(--radius); box-shadow: var(--shadow-lg);
}
.hero__photo::after {
  content: ""; position: absolute; inset: 12px -12px -12px 12px;
  border: 1.5px solid var(--accent-soft); border-radius: var(--radius); z-index: -1;
}
@media (max-width: 780px) {
  .hero { grid-template-columns: 1fr; }
  .hero__photo { max-width: 280px; }
}

/* ============ GENERIC BLOCK ============ */
.block { padding-top: clamp(34px, 5vw, 56px); padding-bottom: clamp(34px, 5vw, 56px); }
.block--alt { background: var(--bg-soft); border-top: 1px solid var(--line); border-bottom: 1px solid var(--line); }

.section-head { max-width: var(--maxw); margin: 0 auto clamp(20px, 3vw, 30px); }
.section-head__label {
  font-family: var(--font-mono); font-size: .72rem; letter-spacing: 1.4px;
  text-transform: uppercase; color: var(--accent-deep); margin: 0 0 6px;
}
.section-head__title {
  font-family: var(--font-disp); font-weight: 600;
  font-size: clamp(1.5rem, 3vw, 2rem); letter-spacing: -.3px; margin: 0;
}

/* ============ TIMELINE (education + experience) ============ */
.timeline { max-width: var(--maxw); margin: 0 auto; display: flex; flex-direction: column; }
.tl {
  display: grid; grid-template-columns: 130px 1fr; gap: clamp(14px, 3vw, 32px);
  padding: 16px 0; border-top: 1px solid var(--line);
  opacity: 0; transform: translateY(14px);
  transition: opacity .5s ease, transform .5s ease;
}
.tl.is-visible { opacity: 1; transform: none; }
.tl:last-child { border-bottom: 1px solid var(--line); }
.tl__when {
  font-family: var(--font-mono); font-size: .8rem; color: var(--accent-deep);
  padding-top: 2px; display: flex; flex-direction: column;
}
.tl__when span { color: var(--ink-soft); font-size: .68rem; margin-top: 1px; }
.tl__body h3 {
  font-family: var(--font-disp); font-weight: 600; font-size: 1.06rem;
  margin: 0 0 3px; display: flex; align-items: center; gap: 8px; flex-wrap: wrap;
}
.tl__tag {
  font-family: var(--font-sans); font-size: .64rem; font-weight: 600;
  letter-spacing: .3px; text-transform: uppercase;
  color: var(--accent-deep); background: var(--accent-soft);
  padding: 2px 8px; border-radius: 999px;
}
.tl__org { color: var(--ink); font-weight: 500; margin: 0 0 4px; font-size: .9rem; }
.tl__note { color: var(--ink-soft); margin: 0; font-size: .88rem; }
@media (max-width: 560px) {
  .tl { grid-template-columns: 1fr; gap: 4px; }
}

/* ============ SELECTED WORK / PAPERS ============ */
.work {
  padding-top: clamp(36px, 5vw, 60px); padding-bottom: clamp(36px, 5vw, 60px);
  background: var(--bg);
}
.papers { max-width: var(--maxw); margin: 0 auto; display: flex; flex-direction: column; gap: clamp(18px, 2.5vw, 28px); }
.paper {
  display: grid; grid-template-columns: 1.05fr 1fr; gap: clamp(16px, 2.5vw, 30px);
  align-items: stretch; background: var(--card); border: 1px solid var(--line);
  border-radius: var(--radius); padding: clamp(14px, 1.6vw, 18px);
  box-shadow: var(--shadow);
  opacity: 0; transform: translateY(18px);
  transition: opacity .55s ease, transform .55s ease, box-shadow .25s ease;
}
.paper.is-visible { opacity: 1; transform: none; }
.paper:hover { box-shadow: var(--shadow-lg); }
.paper--flip .paper__figure { order: 2; }

/* Clickable cards: the title link stretches over the whole card;
   the arXiv / Code / Project links sit above it. */
.paper--link { cursor: pointer; color: inherit; position: relative; }
.paper__stretch::after { content: ""; position: absolute; inset: 0; border-radius: var(--radius); }
.paper__cue a { position: relative; z-index: 1; }
.paper__cue a:hover { text-decoration: underline; }
.paper--link:hover { transform: translateY(-3px); border-color: var(--accent-soft); }
.paper--link:hover .paper__title { color: var(--accent-deep); }
.paper--link:hover .paper__cue { color: var(--accent-deep); gap: 8px; }
.paper__title { transition: color .2s; }
.paper__figure {
  margin: 0; border-radius: 10px; background: #fff; border: 1px solid var(--line);
  display: flex; align-items: center; justify-content: center;
  padding: clamp(12px, 2vw, 22px); min-height: 180px;
}
.paper__figure img { width: 100%; height: auto; max-height: 260px; object-fit: contain; }
.paper__body { display: flex; flex-direction: column; justify-content: center; padding: clamp(6px, 1vw, 12px); }
.paper__meta { display: flex; flex-wrap: wrap; align-items: center; gap: 8px; margin-bottom: 10px; }
.paper__venue {
  font-family: var(--font-mono); font-size: .68rem; letter-spacing: .3px;
  color: var(--accent-deep); background: var(--accent-soft);
  padding: 4px 9px; border-radius: 5px;
}
.paper__role { font-size: .74rem; font-weight: 600; color: var(--ink-soft); }
.paper__award {
  font-size: .68rem; font-weight: 700; color: #fff; background: var(--accent);
  padding: 3px 8px; border-radius: 5px;
}
.paper__title {
  font-family: var(--font-disp); font-weight: 600;
  font-size: clamp(1.08rem, 1.8vw, 1.28rem); line-height: 1.22;
  letter-spacing: -.2px; margin: 0 0 10px;
}
.paper__summary { font-size: .9rem; color: var(--ink-soft); margin: 0 0 14px; line-height: 1.55; }
.paper__summary--empty { font-style: italic; opacity: .55; }
.paper__foot {
  display: flex; align-items: center; justify-content: space-between;
  gap: 12px; margin-top: auto;
}
.paper__tags { display: flex; flex-wrap: wrap; gap: 6px; }
.paper__cue {
  font-family: var(--font-mono); font-size: .72rem; font-weight: 500;
  color: var(--accent); white-space: nowrap;
  display: inline-flex; align-items: center; gap: 4px;
  transition: color .2s, gap .2s;
}
.tag {
  font-size: .7rem; font-weight: 500; color: var(--ink-soft);
  border: 1px solid var(--line); padding: 3px 10px; border-radius: 999px;
}
@media (max-width: 720px) {
  .paper { grid-template-columns: 1fr; }
  .paper--flip .paper__figure { order: 0; }
  .paper__figure { min-height: 0; }
}

/* ============ PROJECTS ============ */
.grid3 {
  max-width: var(--maxw); margin: 0 auto;
  display: grid; grid-template-columns: repeat(3, 1fr); gap: 16px;
}
.mini {
  background: var(--card); border: 1px solid var(--line); border-radius: 12px;
  padding: 16px 18px;
  opacity: 0; transform: translateY(14px);
  transition: opacity .5s ease, transform .5s ease;
}
.mini.is-visible { opacity: 1; transform: none; }
.mini__head { display: flex; justify-content: space-between; align-items: baseline; gap: 10px; margin-bottom: 5px; }
.mini__head h3 { font-family: var(--font-disp); font-weight: 600; font-size: .98rem; margin: 0; }
.mini__head span { font-family: var(--font-mono); font-size: .68rem; color: var(--accent-deep); white-space: nowrap; }
.mini p { margin: 0; color: var(--ink-soft); font-size: .85rem; }
@media (max-width: 720px) { .grid3 { grid-template-columns: 1fr; } }

.tech {
  max-width: var(--maxw); margin: 22px auto 0;
  display: flex; flex-wrap: wrap; gap: 7px;
}
.tech span {
  font-size: .76rem; font-weight: 500; color: var(--ink);
  background: var(--accent-soft); padding: 4px 11px; border-radius: 999px;
}

/* ============ FOOTER ============ */
.footer {
  text-align: center; padding: 30px 24px 38px; color: var(--ink-soft);
  font-size: .8rem; border-top: 1px solid var(--line);
}
.footer__links { display: flex; flex-wrap: wrap; justify-content: center; gap: 10px 24px; margin-bottom: 14px; }
.footer__links a {
  font-weight: 600; color: var(--accent-deep); font-size: .86rem;
  border-bottom: 1.5px solid transparent; transition: border-color .2s;
}
.footer__links a:hover { border-color: var(--accent); }
.footer p { margin: 0; }

@media (prefers-reduced-motion: reduce) {
  * { scroll-behavior: auto !important; }
  .paper, .tl, .mini { opacity: 1 !important; transform: none !important; transition: none; }
}