/* ── Ulter · design system ─────────────────────────────────────────────── */
:root {
  --ink: #0d0d0d;
  --ink-2: #353535;
  --muted: #5f5f66;
  --faint: #8e8e95;
  --line: #ececec;
  --line-2: #e3e3e3;
  --bg: #ffffff;
  --bg-soft: #f7f7f8;
  --bg-softer: #fafafa;
  --radius: 18px;
  --radius-lg: 24px;
  --nav-h: 64px;
  --container: 1216px;
  --font: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
  --shadow-card: 0 1px 2px rgba(0, 0, 0, .04), 0 8px 24px rgba(0, 0, 0, .06);
  --shadow-pop: 0 2px 8px rgba(0, 0, 0, .06), 0 16px 48px rgba(0, 0, 0, .10);
}

* { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
body {
  font-family: var(--font);
  color: var(--ink);
  background: var(--bg);
  font-size: 16px;
  line-height: 1.55;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}
img { max-width: 100%; display: block; }
a { color: inherit; text-decoration: none; }
button { font-family: inherit; }
::selection { background: #0d0d0d; color: #fff; }

.container {
  max-width: var(--container);
  margin: 0 auto;
  padding: 0 24px;
}

/* ── Nav ───────────────────────────────────────────────────────────────── */
.site-nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255, 255, 255, .82);
  backdrop-filter: saturate(180%) blur(16px);
  -webkit-backdrop-filter: saturate(180%) blur(16px);
  border-bottom: 1px solid transparent;
  transition: border-color .25s ease;
}
.site-nav.scrolled { border-bottom-color: var(--line); }
.site-nav.on-dark {
  background: rgba(10, 10, 10, .72);
  color: #f5f5f5;
}
.site-nav.on-dark.scrolled { border-bottom-color: rgba(255, 255, 255, .08); }
.nav-inner {
  max-width: var(--container);
  margin: 0 auto;
  padding: 0 24px;
  height: var(--nav-h);
  display: flex;
  align-items: center;
  gap: 28px;
}
.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 600;
  font-size: 19px;
  letter-spacing: -.01em;
}
.brand img {
  width: 28px;
  height: 28px;
  border-radius: 7px;
}
.nav-links {
  display: flex;
  align-items: center;
  gap: 26px;
  margin-left: 8px;
  flex: 1;
}
.nav-links a {
  font-size: 14.5px;
  font-weight: 500;
  color: var(--muted);
  transition: color .15s ease;
}
.nav-links a:hover, .nav-links a.active { color: var(--ink); }
.on-dark .nav-links a { color: rgba(245, 245, 245, .7); }
.on-dark .nav-links a:hover, .on-dark .nav-links a.active { color: #fff; }
.nav-actions {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-left: auto;
}
.okran-chip {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 34px;
  height: 34px;
  border-radius: 50%;
  overflow: hidden;
  border: 1px solid var(--line-2);
  transition: transform .18s ease, box-shadow .18s ease;
}
.okran-chip img { width: 100%; height: 100%; object-fit: cover; }
.okran-chip:hover { transform: scale(1.06); box-shadow: var(--shadow-card); }
.on-dark .okran-chip { border-color: rgba(255, 255, 255, .18); }

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  border-radius: 999px;
  font-weight: 500;
  font-size: 14.5px;
  padding: 9px 18px;
  border: 1px solid transparent;
  cursor: pointer;
  transition: background .18s ease, color .18s ease, border-color .18s ease, transform .18s ease;
  white-space: nowrap;
}
.btn-dark { background: var(--ink); color: #fff; }
.btn-dark:hover { background: #2f2f2f; }
.btn-light { background: #fff; color: var(--ink); }
.btn-light:hover { background: #ededed; }
.btn-ghost { border-color: var(--line-2); color: var(--ink); background: transparent; }
.btn-ghost:hover { background: var(--bg-soft); }
.btn-ghost-dark { border-color: rgba(255, 255, 255, .28); color: #fff; background: transparent; }
.btn-ghost-dark:hover { background: rgba(255, 255, 255, .1); }
.btn-lg { padding: 13px 26px; font-size: 16px; }

.nav-burger {
  display: none;
  margin-left: auto;
  background: none;
  border: none;
  width: 40px;
  height: 40px;
  cursor: pointer;
  border-radius: 10px;
  align-items: center;
  justify-content: center;
  flex-direction: column;
  gap: 5px;
}
.nav-burger span {
  display: block;
  width: 18px;
  height: 1.8px;
  background: currentColor;
  border-radius: 2px;
  transition: transform .2s ease, opacity .2s ease;
}
.mobile-menu {
  display: none;
  border-top: 1px solid var(--line);
  background: #fff;
  padding: 10px 24px 18px;
}
.mobile-menu a {
  display: block;
  padding: 12px 2px;
  font-size: 16px;
  font-weight: 500;
  border-bottom: 1px solid var(--line);
  color: var(--ink-2);
}
.mobile-menu a:last-child { border-bottom: none; }
.site-nav.menu-open .mobile-menu { display: block; }
.site-nav.on-dark .mobile-menu { background: #0d0d0d; }
.site-nav.on-dark .mobile-menu a { color: #eee; border-color: rgba(255,255,255,.08); }

/* ── Hero (home) ───────────────────────────────────────────────────────── */
.hero {
  min-height: calc(88vh - var(--nav-h));
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: 72px 24px 56px;
}
.hero h1 {
  font-size: clamp(34px, 5.4vw, 56px);
  font-weight: 550;
  letter-spacing: -.025em;
  line-height: 1.12;
  margin-bottom: 34px;
}
.prompt-wrap { width: 100%; max-width: 760px; }
.prompt {
  display: flex;
  align-items: center;
  gap: 10px;
  width: 100%;
  background: #fff;
  border: 1px solid var(--line-2);
  border-radius: 999px;
  padding: 8px 8px 8px 22px;
  box-shadow: 0 2px 6px rgba(0, 0, 0, .03), 0 18px 44px rgba(0, 0, 0, .07);
  transition: box-shadow .2s ease, border-color .2s ease;
}
.prompt:focus-within {
  border-color: #cfcfcf;
  box-shadow: 0 2px 6px rgba(0, 0, 0, .05), 0 22px 56px rgba(0, 0, 0, .11);
}
.prompt input {
  flex: 1;
  border: none;
  outline: none;
  font-size: 17px;
  font-family: inherit;
  color: var(--ink);
  background: transparent;
  min-width: 0;
}
.prompt input::placeholder { color: var(--faint); }
.prompt-send {
  width: 44px;
  height: 44px;
  border-radius: 50%;
  border: none;
  background: var(--ink);
  color: #fff;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  flex: 0 0 auto;
  transition: background .15s ease, transform .15s ease;
}
.prompt-send:hover { background: #2f2f2f; transform: scale(1.04); }
.prompt-send svg { width: 18px; height: 18px; }
.prompt-hint {
  margin-top: 16px;
  font-size: 13px;
  color: var(--faint);
}
.prompt-hint a { color: var(--muted); text-decoration: underline; text-underline-offset: 3px; }
.chips {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  justify-content: center;
  margin-top: 22px;
}
.chip {
  border: 1px solid var(--line-2);
  background: #fff;
  color: var(--muted);
  border-radius: 999px;
  padding: 8px 16px;
  font-size: 13.5px;
  font-weight: 500;
  cursor: pointer;
  transition: background .15s ease, color .15s ease, border-color .15s ease;
}
.chip:hover { background: var(--bg-soft); color: var(--ink); }

/* ── Sections ──────────────────────────────────────────────────────────── */
.section { padding: 72px 0; }
.section-head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 20px;
  margin-bottom: 28px;
}
.section-head h2 {
  font-size: clamp(24px, 3vw, 32px);
  font-weight: 550;
  letter-spacing: -.02em;
}
.section-head .see-all {
  font-size: 14.5px;
  font-weight: 500;
  color: var(--muted);
  transition: color .15s ease;
}
.section-head .see-all:hover { color: var(--ink); }

/* Card grid */
.card-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 20px;
}
.card { display: block; }
.card .thumb {
  aspect-ratio: 4 / 3;
  border-radius: var(--radius);
  overflow: hidden;
  background: var(--bg-soft);
  position: relative;
}
.card .thumb img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  transition: transform .5s cubic-bezier(.2, .6, .2, 1);
}
.card:hover .thumb img { transform: scale(1.045); }
.card .thumb .art { position: absolute; inset: 0; transition: transform .5s cubic-bezier(.2,.6,.2,1); }
.card:hover .thumb .art { transform: scale(1.045); }
.card h3 {
  margin-top: 14px;
  font-size: 16px;
  font-weight: 550;
  letter-spacing: -.01em;
  line-height: 1.35;
}
.card .meta {
  margin-top: 5px;
  font-size: 13px;
  color: var(--faint);
}

/* Abstract gradient art tiles */
.art-1 { background: linear-gradient(135deg, #e8f1ff 0%, #cfe0ff 34%, #f4d9ff 68%, #ffe3ec 100%); }
.art-2 { background: linear-gradient(120deg, #dff3e9 0%, #bfe8d9 40%, #d7e9ff 78%, #e8e0ff 100%); }
.art-3 { background: linear-gradient(130deg, #fff0dc 0%, #ffd9c2 38%, #ffc9d8 72%, #e6d4ff 100%); }
.art-4 { background: linear-gradient(140deg, #101010 0%, #23252b 52%, #3a3f49 100%); }

/* Split feature */
.split {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 56px;
  align-items: center;
}
.split .visual {
  border-radius: var(--radius-lg);
  overflow: hidden;
  box-shadow: var(--shadow-card);
}
.split h2 {
  font-size: clamp(26px, 3.4vw, 38px);
  font-weight: 550;
  letter-spacing: -.022em;
  line-height: 1.15;
  margin-bottom: 16px;
}
.split p.lede { font-size: 17px; color: var(--muted); margin-bottom: 22px; }
.split .actions { display: flex; gap: 12px; flex-wrap: wrap; }

/* Model tiles */
.model-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 16px;
}
.model-tile {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 22px 20px;
  background: #fff;
  transition: box-shadow .2s ease, transform .2s ease;
}
.model-tile:hover { box-shadow: var(--shadow-card); transform: translateY(-2px); }
.model-tile .dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  margin-bottom: 14px;
}
.model-tile h4 { font-size: 15.5px; font-weight: 600; letter-spacing: -.01em; }
.model-tile p { font-size: 13.5px; color: var(--muted); margin-top: 4px; }

/* Feature cards (okran page) */
.feature-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 20px;
}
.feature-card {
  border: 1px solid var(--line);
  border-radius: var(--radius-lg);
  background: #fff;
  padding: 28px 26px;
  transition: box-shadow .2s ease, transform .2s ease;
}
.feature-card:hover { box-shadow: var(--shadow-card); transform: translateY(-2px); }
.feature-card .icon {
  width: 40px;
  height: 40px;
  border-radius: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 18px;
  background: var(--bg-soft);
  font-size: 18px;
}
.feature-card h3 { font-size: 17px; font-weight: 600; letter-spacing: -.012em; margin-bottom: 8px; }
.feature-card p { font-size: 14.5px; color: var(--muted); }

/* CTA band */
.cta-band {
  background: #0d0d0d;
  color: #fff;
  border-radius: var(--radius-lg);
  padding: clamp(44px, 6vw, 80px) clamp(28px, 5vw, 72px);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 32px;
  flex-wrap: wrap;
  position: relative;
  overflow: hidden;
}
.cta-band::after {
  content: "";
  position: absolute;
  right: -140px;
  top: -140px;
  width: 420px;
  height: 420px;
  background: radial-gradient(circle at center, rgba(64, 106, 255, .55), transparent 65%);
  pointer-events: none;
}
.cta-band h2 {
  font-size: clamp(26px, 3.6vw, 40px);
  font-weight: 550;
  letter-spacing: -.022em;
  line-height: 1.12;
}
.cta-band p { color: rgba(255, 255, 255, .62); margin-top: 10px; font-size: 16px; }
.cta-band .actions { display: flex; gap: 12px; flex-wrap: wrap; position: relative; z-index: 1; }

/* ── Article (how / legal) ─────────────────────────────────────────────── */
.article {
  max-width: 720px;
  margin: 0 auto;
  padding: 64px 24px 96px;
}
.article .eyebrow {
  font-size: 13.5px;
  font-weight: 500;
  color: var(--faint);
  margin-bottom: 18px;
  display: flex;
  gap: 8px;
  align-items: center;
  flex-wrap: wrap;
}
.article .eyebrow a { color: var(--muted); }
.article .eyebrow a:hover { color: var(--ink); }
.article h1 {
  font-size: clamp(32px, 4.6vw, 48px);
  font-weight: 550;
  letter-spacing: -.026em;
  line-height: 1.1;
  margin-bottom: 22px;
}
.article .lede {
  font-size: 19px;
  line-height: 1.6;
  color: var(--muted);
  margin-bottom: 36px;
}
.article figure {
  margin: 36px 0;
}
.article figure img { border-radius: var(--radius-lg); width: 100%; }
.article figcaption { font-size: 13px; color: var(--faint); margin-top: 10px; }
.article h2 {
  font-size: 25px;
  font-weight: 600;
  letter-spacing: -.018em;
  margin: 44px 0 14px;
}
.article h3 {
  font-size: 18.5px;
  font-weight: 600;
  letter-spacing: -.012em;
  margin: 30px 0 10px;
}
.article p { margin-bottom: 16px; font-size: 16.5px; line-height: 1.7; color: var(--ink-2); }
.article ul, .article ol { margin: 0 0 18px 22px; }
.article li { margin-bottom: 9px; font-size: 16.5px; line-height: 1.65; color: var(--ink-2); }
.article blockquote {
  border-left: 3px solid var(--ink);
  padding: 4px 0 4px 22px;
  margin: 30px 0;
  font-size: 19px;
  line-height: 1.55;
  font-weight: 500;
  letter-spacing: -.012em;
  color: var(--ink);
}
.article .note {
  background: var(--bg-soft);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 20px 22px;
  font-size: 15px;
  color: var(--muted);
  margin: 28px 0;
}
.article .note strong { color: var(--ink-2); }
.article table {
  width: 100%;
  border-collapse: collapse;
  font-size: 14.5px;
  margin: 24px 0;
}
.article th, .article td {
  text-align: left;
  padding: 10px 12px;
  border-bottom: 1px solid var(--line);
  vertical-align: top;
}
.article th { font-weight: 600; background: var(--bg-soft); }
.article a.inline { text-decoration: underline; text-underline-offset: 3px; text-decoration-color: #c9c9c9; }
.article a.inline:hover { text-decoration-color: var(--ink); }
.article .updated { font-size: 13.5px; color: var(--faint); margin-bottom: 40px; }

/* Numbered steps */
.steps { counter-reset: step; margin: 26px 0; display: grid; gap: 14px; }
.step {
  display: flex;
  gap: 18px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 20px 22px;
  background: #fff;
}
.step::before {
  counter-increment: step;
  content: counter(step);
  flex: 0 0 30px;
  height: 30px;
  border-radius: 50%;
  background: var(--ink);
  color: #fff;
  font-size: 14px;
  font-weight: 600;
  display: flex;
  align-items: center;
  justify-content: center;
  margin-top: 2px;
}
.step h4 { font-size: 16px; font-weight: 600; margin-bottom: 4px; }
.step p { font-size: 14.5px; color: var(--muted); margin: 0; line-height: 1.6; }

/* Roster */
.roster { display: grid; grid-template-columns: repeat(2, 1fr); gap: 14px; margin: 26px 0; }
.roster .member {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 18px 20px;
  background: #fff;
}
.roster .member h4 { font-size: 15.5px; font-weight: 600; display: flex; align-items: center; gap: 9px; }
.roster .member h4 .dot { width: 9px; height: 9px; border-radius: 50%; display: inline-block; }
.roster .member p { font-size: 13.5px; color: var(--muted); margin: 6px 0 0; line-height: 1.55; }

.dot-blue { background: #3b82f6; }
.dot-green { background: #10b981; }
.dot-purple { background: #8b5cf6; }
.dot-orange { background: #f59e0b; }

/* ── Research index ────────────────────────────────────────────────────── */
.page-hero {
  padding: 84px 0 48px;
}
.page-hero h1 {
  font-size: clamp(38px, 5.4vw, 60px);
  font-weight: 550;
  letter-spacing: -.028em;
  line-height: 1.05;
  margin-bottom: 16px;
}
.page-hero p {
  font-size: 18px;
  color: var(--muted);
  max-width: 620px;
}
.paper-featured {
  display: grid;
  grid-template-columns: 1.15fr 1fr;
  border: 1px solid var(--line);
  border-radius: var(--radius-lg);
  overflow: hidden;
  margin-bottom: 24px;
  background: #fff;
  transition: box-shadow .2s ease;
}
.paper-featured:hover { box-shadow: var(--shadow-card); }
.paper-featured .art { min-height: 300px; }
.paper-featured .body { padding: clamp(26px, 4vw, 48px); display: flex; flex-direction: column; justify-content: center; }
.paper-featured .tag { font-size: 13px; font-weight: 500; color: var(--faint); margin-bottom: 12px; }
.paper-featured h3 { font-size: clamp(21px, 2.6vw, 28px); font-weight: 550; letter-spacing: -.02em; line-height: 1.22; margin-bottom: 12px; }
.paper-featured p { font-size: 15px; color: var(--muted); margin-bottom: 20px; }
.paper-featured .read { font-size: 14.5px; font-weight: 550; }
.paper-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 20px; }

/* ── PDF viewer ────────────────────────────────────────────────────────── */
.viewer-body { background: var(--bg-soft); min-height: 100vh; }
.viewer-bar {
  position: sticky;
  top: 0;
  z-index: 60;
  display: flex;
  align-items: center;
  gap: 16px;
  padding: 0 20px;
  height: 58px;
  background: rgba(255, 255, 255, .86);
  backdrop-filter: saturate(180%) blur(14px);
  -webkit-backdrop-filter: saturate(180%) blur(14px);
  border-bottom: 1px solid var(--line);
}
.viewer-bar .back {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 14px;
  font-weight: 500;
  color: var(--muted);
  flex: 0 0 auto;
}
.viewer-bar .back:hover { color: var(--ink); }
.viewer-bar .vtitle {
  flex: 1;
  font-size: 14px;
  font-weight: 550;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  text-align: center;
  color: var(--ink-2);
}
.viewer-bar .tools { display: flex; align-items: center; gap: 8px; flex: 0 0 auto; }
.viewer-bar .pageinfo { font-size: 13px; color: var(--faint); min-width: 74px; text-align: center; }
.zoom-btn {
  width: 32px;
  height: 32px;
  border-radius: 50%;
  border: 1px solid var(--line-2);
  background: #fff;
  color: var(--ink-2);
  font-size: 16px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background .15s ease;
}
.zoom-btn:hover { background: var(--bg-soft); }
.viewer-bar .btn { padding: 7px 15px; font-size: 13.5px; }
#pdf-scroll { padding: 28px 16px 64px; }
#pdf-pages { display: flex; flex-direction: column; align-items: center; gap: 22px; }
.pdf-page-card {
  background: #fff;
  border-radius: 8px;
  box-shadow: 0 1px 3px rgba(0, 0, 0, .07), 0 10px 30px rgba(0, 0, 0, .07);
  overflow: hidden;
  line-height: 0;
}
.pdf-page-card canvas { width: 100%; height: auto; }
.viewer-loading {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 16px;
  padding: 90px 0;
  color: var(--faint);
  font-size: 14px;
}
.spinner {
  width: 26px;
  height: 26px;
  border-radius: 50%;
  border: 2.5px solid var(--line-2);
  border-top-color: var(--ink);
  animation: spin .8s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }

/* ── Footer ────────────────────────────────────────────────────────────── */
.site-footer {
  border-top: 1px solid var(--line);
  padding: 56px 0 40px;
  margin-top: 40px;
  background: var(--bg);
}
.footer-grid {
  display: grid;
  grid-template-columns: 1.4fr repeat(4, 1fr);
  gap: 32px;
}
.footer-brand { display: flex; flex-direction: column; gap: 14px; }
.footer-brand .brand img { width: 30px; height: 30px; }
.footer-brand p { font-size: 13.5px; color: var(--faint); max-width: 240px; }
.footer-col h5 {
  font-size: 13px;
  font-weight: 600;
  color: var(--ink);
  margin-bottom: 14px;
}
.footer-col a {
  display: block;
  font-size: 13.5px;
  color: var(--muted);
  padding: 4.5px 0;
  transition: color .15s ease;
}
.footer-col a:hover { color: var(--ink); }
.footer-bottom {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  flex-wrap: wrap;
  margin-top: 44px;
  padding-top: 24px;
  border-top: 1px solid var(--line);
  font-size: 13px;
  color: var(--faint);
}
.footer-bottom .links { display: flex; gap: 18px; }
.footer-bottom a:hover { color: var(--ink); }

/* ── Dark hero (okran page) ────────────────────────────────────────────── */
.dark-hero {
  background: #0a0a0a;
  color: #fff;
  padding: 96px 0 88px;
  text-align: center;
  position: relative;
  overflow: hidden;
}
.dark-hero::before {
  content: "";
  position: absolute;
  left: 50%;
  bottom: -320px;
  transform: translateX(-50%);
  width: 900px;
  height: 620px;
  background: radial-gradient(ellipse at center, rgba(56, 98, 255, .5), rgba(120, 60, 255, .18) 55%, transparent 75%);
  pointer-events: none;
}
.dark-hero .inner { position: relative; z-index: 1; }
.dark-hero .mark {
  width: 76px;
  height: 76px;
  border-radius: 50%;
  margin: 0 auto 26px;
  overflow: hidden;
  box-shadow: 0 0 0 1px rgba(255, 255, 255, .12), 0 20px 60px rgba(0, 0, 0, .5);
}
.dark-hero .mark img { width: 100%; height: 100%; object-fit: cover; }
.dark-hero h1 {
  font-size: clamp(40px, 6.4vw, 72px);
  font-weight: 550;
  letter-spacing: -.03em;
  line-height: 1.02;
}
.dark-hero .sub {
  font-size: clamp(17px, 2vw, 20px);
  color: rgba(255, 255, 255, .64);
  max-width: 560px;
  margin: 18px auto 34px;
}
.dark-hero .actions { display: flex; gap: 14px; justify-content: center; flex-wrap: wrap; }

.section-sub {
  font-size: 16.5px;
  color: var(--muted);
  max-width: 640px;
  margin-top: -16px;
  margin-bottom: 30px;
}

/* ── Responsive ────────────────────────────────────────────────────────── */
@media (max-width: 980px) {
  .card-grid { grid-template-columns: repeat(2, 1fr); }
  .model-grid { grid-template-columns: repeat(2, 1fr); }
  .feature-grid { grid-template-columns: repeat(2, 1fr); }
  .split { grid-template-columns: 1fr; gap: 32px; }
  .paper-featured { grid-template-columns: 1fr; }
  .paper-featured .art { min-height: 200px; }
  .paper-grid { grid-template-columns: repeat(2, 1fr); }
  .footer-grid { grid-template-columns: repeat(2, 1fr); }
}
@media (max-width: 720px) {
  .nav-links, .nav-actions .btn { display: none; }
  .nav-burger { display: flex; }
  .hero { padding-top: 40px; min-height: calc(78vh - var(--nav-h)); }
  .section { padding: 52px 0; }
  .viewer-bar .vtitle { display: none; }
}
@media (max-width: 560px) {
  .card-grid, .model-grid, .feature-grid, .paper-grid, .roster { grid-template-columns: 1fr; }
  .footer-grid { grid-template-columns: 1fr 1fr; }
  .cta-band { border-radius: var(--radius); }
}

/* ── Help center ───────────────────────────────────────────────────────── */
.help-hero {
  padding: 76px 0 44px;
  text-align: center;
}
.help-hero h1 {
  font-size: clamp(32px, 4.6vw, 48px);
  font-weight: 550;
  letter-spacing: -.025em;
  margin-bottom: 26px;
}
.help-search {
  display: flex;
  align-items: center;
  gap: 10px;
  max-width: 640px;
  margin: 0 auto;
  background: #fff;
  border: 1px solid var(--line-2);
  border-radius: 999px;
  padding: 6px 8px 6px 20px;
  box-shadow: 0 2px 6px rgba(0,0,0,.03), 0 14px 36px rgba(0,0,0,.06);
  transition: box-shadow .2s ease, border-color .2s ease;
}
.help-search:focus-within { border-color: #cfcfcf; box-shadow: 0 2px 6px rgba(0,0,0,.05), 0 18px 44px rgba(0,0,0,.1); }
.help-search svg { color: var(--faint); flex: 0 0 auto; }
.help-search input {
  flex: 1;
  border: none;
  outline: none;
  font-size: 16px;
  font-family: inherit;
  background: transparent;
  padding: 8px 0;
  min-width: 0;
}
.help-search input::placeholder { color: var(--faint); }
.help-cats {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  justify-content: center;
  margin-top: 22px;
}
.help-section { margin-bottom: 20px; }
.help-section h2 {
  font-size: 21px;
  font-weight: 600;
  letter-spacing: -.015em;
  padding-top: 34px;
  margin-bottom: 14px;
}
details.qa {
  border: 1px solid var(--line);
  border-radius: 14px;
  background: #fff;
  margin-bottom: 10px;
  overflow: hidden;
  transition: box-shadow .2s ease;
}
details.qa:hover { box-shadow: var(--shadow-card); }
details.qa summary {
  cursor: pointer;
  list-style: none;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 16px 20px;
  font-size: 15.5px;
  font-weight: 550;
  letter-spacing: -.008em;
}
details.qa summary::-webkit-details-marker { display: none; }
details.qa summary::after {
  content: "+";
  font-size: 20px;
  font-weight: 400;
  color: var(--faint);
  transition: transform .2s ease;
  flex: 0 0 auto;
}
details.qa[open] summary::after { transform: rotate(45deg); }
details.qa .a {
  padding: 0 20px 18px;
  font-size: 14.5px;
  line-height: 1.65;
  color: var(--ink-2);
}
details.qa .a p { margin-bottom: 10px; }
details.qa .a p:last-child { margin-bottom: 0; }
details.qa .a ol, details.qa .a ul { margin: 0 0 10px 20px; }
details.qa .a li { margin-bottom: 5px; }
details.qa .a a { text-decoration: underline; text-underline-offset: 3px; text-decoration-color: #c9c9c9; }
details.qa .a a:hover { text-decoration-color: var(--ink); }
details.qa .a code {
  background: var(--bg-soft);
  border: 1px solid var(--line);
  border-radius: 6px;
  padding: 1px 6px;
  font-size: 13px;
}
.help-empty {
  display: none;
  text-align: center;
  color: var(--faint);
  padding: 48px 0;
  font-size: 15px;
}
.help-contact {
  margin-top: 44px;
  border: 1px solid var(--line);
  border-radius: var(--radius-lg);
  background: var(--bg-soft);
  padding: 30px 28px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
  flex-wrap: wrap;
}
.help-contact h3 { font-size: 18px; font-weight: 600; letter-spacing: -.012em; }
.help-contact p { font-size: 14px; color: var(--muted); margin-top: 4px; }

/* ── Theming: dark by default, light via html[data-theme="light"] ─────── */
:root {
  --ink: #ececec;
  --ink-2: #c9c9ce;
  --muted: #9a9aa2;
  --faint: #6f6f78;
  --line: #232327;
  --line-2: #2e2e34;
  --bg: #0d0d0f;
  --bg-soft: #161619;
  --bg-softer: #121214;
  --card: #151518;
  --nav-glass: rgba(13, 13, 15, .8);
  --btn-hover: #d7d7d7;
  --sel-bg: #ececec;
  --sel-fg: #0d0d0f;
  --shadow-card: 0 1px 2px rgba(0, 0, 0, .3), 0 8px 24px rgba(0, 0, 0, .35);
  --shadow-pop: 0 2px 8px rgba(0, 0, 0, .35), 0 16px 48px rgba(0, 0, 0, .5);
  color-scheme: dark;
}
html[data-theme="light"] {
  --ink: #0d0d0d;
  --ink-2: #353535;
  --muted: #5f5f66;
  --faint: #8e8e95;
  --line: #ececec;
  --line-2: #e3e3e3;
  --bg: #ffffff;
  --bg-soft: #f7f7f8;
  --bg-softer: #fafafa;
  --card: #ffffff;
  --nav-glass: rgba(255, 255, 255, .82);
  --btn-hover: #2f2f2f;
  --sel-bg: #0d0d0d;
  --sel-fg: #ffffff;
  --shadow-card: 0 1px 2px rgba(0, 0, 0, .04), 0 8px 24px rgba(0, 0, 0, .06);
  --shadow-pop: 0 2px 8px rgba(0, 0, 0, .06), 0 16px 48px rgba(0, 0, 0, .10);
  color-scheme: light;
}

::selection { background: var(--sel-bg); color: var(--sel-fg); }

/* Re-point hardcoded surfaces at theme tokens */
.site-nav { background: var(--nav-glass); }
.site-nav.on-dark { background: rgba(10, 10, 10, .72); }
.mobile-menu { background: var(--bg); }
.mobile-menu a { color: var(--ink-2); border-color: var(--line); }

.btn-dark { background: var(--ink); color: var(--bg); }
.btn-dark:hover { background: var(--btn-hover); }

.prompt { background: var(--card); }
.prompt:focus-within { border-color: var(--line-2); }
.prompt input { color: var(--ink); }
.prompt-send { background: var(--ink); color: var(--bg); }
.prompt-send:hover { background: var(--btn-hover); }
.chip { background: var(--card); }
.chip:hover { background: var(--bg-soft); }

.model-tile, .feature-card, .step, .roster .member, .paper-featured, details.qa {
  background: var(--card);
}
.step::before { background: var(--ink); color: var(--bg); }

.cta-band { border: 1px solid rgba(255, 255, 255, .09); }
.cta-band .btn-dark { background: #fff; color: #0d0d0d; }
.cta-band .btn-dark:hover { background: #ededed; }

.viewer-bar { background: var(--nav-glass); }
.zoom-btn { background: var(--card); color: var(--ink-2); }
.zoom-btn:hover { background: var(--bg-soft); }
.pdf-page-card { background: #fff; }

.help-search { background: var(--card); }
.help-search:focus-within { border-color: var(--line-2); }
.help-search input { color: var(--ink); }

/* Theme toggle */
.theme-toggle {
  width: 34px;
  height: 34px;
  border-radius: 50%;
  border: 1px solid var(--line-2);
  background: transparent;
  color: var(--muted);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  flex: 0 0 auto;
  transition: color .15s ease, background .15s ease, transform .18s ease;
}
.theme-toggle:hover { color: var(--ink); background: var(--bg-soft); transform: scale(1.06); }
.on-dark .theme-toggle { border-color: rgba(255, 255, 255, .18); color: rgba(245, 245, 245, .7); }
.on-dark .theme-toggle:hover { color: #fff; background: rgba(255, 255, 255, .1); }
.theme-toggle .moon { display: none; }
.theme-toggle .sun { display: block; }
html[data-theme="light"] .theme-toggle .moon { display: block; }
html[data-theme="light"] .theme-toggle .sun { display: none; }

/* Dark-mode softening for bright artwork & imagery */
html:not([data-theme="light"]) .art-1 { background: linear-gradient(135deg, #1c2a45 0%, #24406e 34%, #4a2b5e 68%, #5e2740 100%); }
html:not([data-theme="light"]) .art-2 { background: linear-gradient(120deg, #14352a 0%, #1d4a3d 40%, #1e3a5c 78%, #35305e 100%); }
html:not([data-theme="light"]) .art-3 { background: linear-gradient(130deg, #45301a 0%, #5c3620 38%, #5e2436 72%, #3a2a56 100%); }
html:not([data-theme="light"]) .card .thumb img,
html:not([data-theme="light"]) .split .visual img,
html:not([data-theme="light"]) .article figure img { filter: brightness(.92); }

/* ── Fix: light buttons keep dark text in every theme ──────────────────── */
.btn-light { background: #fff; color: #0d0d0d; }
.btn-light:hover { background: #e6e6e6; color: #0d0d0d; }

/* ── Mobile refinements ────────────────────────────────────────────────── */
@media (max-width: 720px) {
  .section-head { flex-wrap: wrap; }
  .hero { padding-left: 18px; padding-right: 18px; }
  .split .actions .btn, .cta-band .actions .btn { flex: 0 1 auto; }
  .article table { display: block; overflow-x: auto; -webkit-overflow-scrolling: touch; }
  .viewer-bar { padding: 0 12px; gap: 10px; }
  .viewer-bar .back { font-size: 13px; }
  .viewer-bar .btn { padding: 7px 12px; font-size: 13px; }
  .footer-grid { gap: 24px; }
}
@media (max-width: 480px) {
  .container { padding: 0 18px; }
  .nav-inner { padding: 0 16px; gap: 16px; }
  .hero { min-height: calc(72vh - var(--nav-h)); padding-top: 32px; }
  .hero h1 { margin-bottom: 26px; }
  .prompt { padding: 6px 6px 6px 16px; }
  .prompt-send { width: 40px; height: 40px; }
  .chips { gap: 8px; }
  .chip { padding: 7px 13px; font-size: 13px; }
  .section { padding: 44px 0; }
  .btn-lg { padding: 12px 20px; font-size: 15px; }
  .cta-band { padding: 36px 22px; }
  .cta-band .actions { width: 100%; }
  .dark-hero { padding: 68px 0 60px; }
  .dark-hero .mark { width: 64px; height: 64px; }
  .page-hero { padding: 56px 0 30px; }
  .article { padding: 44px 18px 72px; }
  .article blockquote { font-size: 17px; padding-left: 16px; }
  .step { padding: 16px 16px; gap: 13px; }
  .paper-featured .body { padding: 22px 20px; }
  .help-hero { padding: 52px 0 32px; }
  .help-search { max-width: 100%; }
  .help-contact { padding: 22px 20px; }
  .viewer-bar .pageinfo { min-width: 0; }
  #pdf-scroll { padding: 16px 8px 48px; }
  .footer-grid { grid-template-columns: 1fr; gap: 20px; }
  .footer-bottom { flex-direction: column; align-items: flex-start; }
}