:root {
  --bg: #ffffff;
  --bg-alt: #f7f8fa;
  --fg: #1a1a1f;
  --fg-soft: #4a4a55;
  --fg-muted: #7a7a85;
  --border: #e5e7eb;
  --accent: #2b50ec;
  --accent-soft: #eaefff;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0d0e12;
    --bg-alt: #14161c;
    --fg: #ececf1;
    --fg-soft: #c2c2cc;
    --fg-muted: #8a8a96;
    --border: #2a2c34;
    --accent: #6f8eff;
    --accent-soft: #1a2240;
  }
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--fg);
  font-family: 'Inter', system-ui, -apple-system, Segoe UI, Roboto, sans-serif;
  font-size: 16px;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

.container {
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 1.25rem;
}

.hero {
  padding: 6rem 0 5rem;
  text-align: center;
  background: radial-gradient(ellipse at top, var(--accent-soft), transparent 60%);
}

.title {
  font-size: clamp(1.9rem, 4.2vw, 3.1rem);
  line-height: 1.15;
  font-weight: 700;
  letter-spacing: -0.02em;
  margin: 0 0 1.5rem;
}

/* ---------- Authors & affiliations ---------- */
.authors,
.affiliations {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 0.15rem 0.9rem;
}

.authors {
  font-size: 1.08rem;
  font-weight: 600;
}

.authors li { white-space: nowrap; }

.authors a {
  color: var(--fg);
  text-decoration: none;
}
.authors a:hover { color: var(--accent); text-decoration: underline; }

.authors sup,
.affiliations sup {
  color: var(--accent);
  font-weight: 600;
}

.affiliations {
  margin-top: 0.6rem;
  font-size: 0.95rem;
  color: var(--fg-soft);
}

/* ---------- Link buttons ---------- */
.links {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 0.6rem;
  margin-top: 1.6rem;
}

.link-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  font-size: 0.92rem;
  font-weight: 600;
  color: #fff;
  background: var(--fg);
  padding: 0.5rem 1.05rem;
  border-radius: 999px;
  text-decoration: none;
  transition: transform 0.12s ease, background 0.12s ease;
}
.link-btn:hover { background: var(--accent); transform: translateY(-1px); }

@media (prefers-color-scheme: dark) {
  .link-btn { color: var(--bg); background: var(--fg); }
  .link-btn:hover { color: #fff; }
}

.link-ico {
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 0.9em;
}

/* ---------- Sticky section nav ---------- */
.section-nav {
  position: sticky;
  top: 0;
  z-index: 10;
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: saturate(180%) blur(10px);
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
}

.section-nav-inner {
  display: flex;
  flex-wrap: nowrap;
  gap: 0.35rem 1.4rem;
  overflow-x: auto;
  padding-top: 0.7rem;
  padding-bottom: 0.7rem;
  -webkit-overflow-scrolling: touch;
  scrollbar-width: none;
}
.section-nav-inner::-webkit-scrollbar { display: none; }

.section-nav-inner a {
  white-space: nowrap;
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--fg-muted);
  text-decoration: none;
}
.section-nav-inner a:hover { color: var(--accent); }

html { scroll-behavior: smooth; }
:target { scroll-margin-top: 4rem; }

/* ---------- Sections ---------- */
.section { padding: 3rem 0; }
.section + .section { border-top: 1px solid var(--border); }

/* ---------- Teaser carousel ---------- */
.teaser-cap {
  text-align: center;
  color: var(--fg-soft);
  font-size: 1.02rem;
  margin: 1.35rem auto 0;
  max-width: 62ch;
}

.carousel { position: relative; }
.carousel-track {
  display: flex;
  overflow-x: auto;
  scroll-snap-type: x mandatory;
  scroll-behavior: smooth;
  gap: 1rem;
  scrollbar-width: none;
  -webkit-overflow-scrolling: touch;
  --per: 1;
}
.carousel-track::-webkit-scrollbar { display: none; }

.slide {
  flex: 0 0 calc((100% - (var(--per) - 1) * 1rem) / var(--per));
  scroll-snap-align: start;
}
.slide-tag {
  font-size: 0.78rem;
  font-weight: 600;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--fg-muted);
  text-align: center;
  margin: 0 0 0.6rem;
}
.slide-tag a {
  color: inherit;
  text-decoration: underline;
  text-underline-offset: 2px;
}
.slide-tag a:hover { text-decoration-thickness: 2px; }

.stack .inputs-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.6rem;
  margin-bottom: 0.6rem;
}
.stack .vid-cell { aspect-ratio: 16 / 9; }

.car-btn {
  position: absolute;
  top: 44%;
  transform: translateY(-50%);
  width: 2.6rem;
  height: 2.6rem;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--fg);
  font-size: 1.2rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 5;
  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.12);
  transition: background 0.12s ease, color 0.12s ease, border-color 0.12s ease;
}
.car-btn:hover { background: var(--accent); color: #fff; border-color: var(--accent); }
.car-btn.prev { left: -0.5rem; }
.car-btn.next { right: -0.5rem; }

.dots {
  display: flex;
  justify-content: center;
  gap: 0.5rem;
  margin-top: 1rem;
}
.dot {
  width: 0.55rem;
  height: 0.55rem;
  border-radius: 999px;
  border: none;
  background: var(--border);
  cursor: pointer;
  padding: 0;
  transition: background 0.15s ease, transform 0.15s ease;
}
.dot.active { background: var(--accent); transform: scale(1.25); }

@media (max-width: 720px) {
  .car-btn.prev { left: 0; }
  .car-btn.next { right: 0; }
}

/* Teaser input/output treatment — tinted panels */
.io-v2 .io-panel {
  position: relative;
  border-radius: 9px;
  padding: 0.4rem;
}
.io-v2 .io-panel-in { background: var(--bg-alt); border: 1px solid var(--border); }
.io-v2 .io-panel-out { background: var(--accent-soft); border: 1px solid var(--accent); margin-top: 0.35rem; }
.io-v2 .io-head {
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}
/* input label sits on the same line as the "Reference" / "Masked visual action" captions */
.io-v2 .io-panel-in .io-head {
  position: absolute;
  top: 0.2rem;
  left: 0.55rem;
  z-index: 2;
  color: var(--fg-muted);
}
/* output label above the video, as before */
.io-v2 .io-panel-out .io-head {
  color: var(--accent);
  margin: 0.1rem 0 0.35rem 0.15rem;
}
.io-v2 .inputs-row { gap: 0.4rem; margin-bottom: 0; }

/* On phones the long "Masked visual action" label wraps to two lines while
   "Reference" stays one line; reserve equal (bottom-aligned) label height so
   the two input videos stay aligned. */
@media (max-width: 640px) {
  /* the section nav is too cramped to be useful on phones */
  .section-nav { display: none; }

  .io-v2 .inputs-row .cell-label {
    display: flex;
    align-items: flex-end;
    justify-content: center;
    line-height: 1.15;
    min-height: 2.3em;
  }
}

/* ---------- TL;DR ---------- */
.tldr {
  display: flex;
  align-items: baseline;
  gap: 1rem;
  background: var(--accent-soft);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 1.25rem 1.5rem;
}

.tldr-tag {
  flex: none;
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--accent);
}

.tldr-text {
  margin: 0;
  font-size: 1.1rem;
  line-height: 1.55;
  color: var(--fg);
}

@media (max-width: 560px) {
  .tldr { flex-direction: column; gap: 0.5rem; }
}

/* ---------- Overview figure ---------- */
.overview-fig { margin: 0; }

.overview-fig img {
  width: 100%;
  height: auto;
  display: block;
  border: 1px solid var(--border);
  border-radius: 8px;
  /* the figure art is transparent — keep it on white in both themes so it never looks off */
  background: #ffffff;
  padding: 1rem;
}

.overview-fig figcaption {
  margin-top: 0.75rem;
  font-size: 0.9rem;
  color: var(--fg-muted);
  text-align: center;
}

h2 {
  font-size: clamp(1.5rem, 2.6vw, 2rem);
  letter-spacing: -0.01em;
  margin: 0 0 0.75rem;
  font-weight: 700;
}

.lede {
  color: var(--fg-soft);
  font-size: 1.02rem;
  margin: 0 0 2rem;
}
.lede a {
  color: var(--accent);
  text-decoration: underline;
  text-underline-offset: 2px;
}

/* ---------- Policy eval examples ---------- */
.example { margin: 2rem 0 2.5rem; }
.example + .example { margin-top: 3rem; }

.example-title {
  font-size: 1.1rem;
  font-weight: 600;
  margin: 0 0 0.85rem;
  color: var(--fg);
}

.example-note {
  font-size: 0.92rem;
  color: var(--fg-muted);
  margin: -0.4rem 0 1rem;
  max-width: 780px;
}

/*
   Two-column layout per example:
     - Left: reference image (single-cell size, vertically centered)
     - Right: 3-col grid containing column labels + two rows of rollouts
*/
.example-grid {
  display: grid;
  grid-template-columns: minmax(180px, 1fr) minmax(0, 3fr);
  gap: 1.25rem;
  align-items: center;
}

.ref-col {
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
}

.ref-img {
  width: 100%;
  aspect-ratio: 16 / 10;
  object-fit: cover;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--bg-alt);
  display: block;
}

.rollouts {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.4rem 0.6rem;
}

.vid-cell {
  width: 100%;
  aspect-ratio: 16 / 10;
  object-fit: cover;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--bg-alt);
  display: block;
}

.cell-label {
  font-size: 0.78rem;
  font-weight: 600;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--fg-muted);
  padding: 0 0.15rem;
  text-align: center;
}

@media (max-width: 720px) {
  .example-grid {
    grid-template-columns: 1fr;
    gap: 1rem;
  }
}

/* ---------- Comparison-with-baselines grid ---------- */
.cmp-grid {
  display: grid;
  gap: 0.4rem 0.6rem;
  margin: 0 0 2rem;
}
.cmp-grid--5 { grid-template-columns: repeat(5, minmax(0, 1fr)); }
.cmp-grid--4 { grid-template-columns: repeat(4, minmax(0, 1fr)); }
.cmp-grid--3 { grid-template-columns: repeat(3, minmax(0, 1fr)); }
.cmp-grid--2 { grid-template-columns: repeat(2, minmax(0, 1fr)); }

.cmp-grid .vid-cell {
  width: 100%;
  aspect-ratio: 16 / 9;
}

@media (max-width: 720px) {
  /* keep comparisons side-by-side (that's the point) and labeled; scroll sideways
     so each cell stays a usable size instead of collapsing to one column */
  .cmp-grid {
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
    gap: 0.3rem 0.35rem;
    padding-bottom: 0.35rem;
  }
  .cmp-grid--5 { grid-template-columns: repeat(5, minmax(30vw, 1fr)); }
  .cmp-grid--4 { grid-template-columns: repeat(4, minmax(32vw, 1fr)); }
  .cmp-grid--3 { grid-template-columns: repeat(3, minmax(30vw, 1fr)); }
  .cmp-grid--2 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .cmp-grid > .cell-label { font-size: 0.6rem; letter-spacing: 0.02em; padding: 0; }
}

/* ---------- Reference frame + action->motion triptych ---------- */
.single-ref {
  margin: 0 auto 1.75rem;
  max-width: 420px;
  text-align: center;
}
.single-ref img {
  width: 100%;
  aspect-ratio: 16 / 9;
  object-fit: cover;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--bg-alt);
  display: block;
}
.single-ref figcaption {
  margin-top: 0.5rem;
  font-size: 0.78rem;
  font-weight: 600;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--fg-muted);
}

.io-flow {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.4rem 0.8rem;
  margin: 0 0 1rem;
}
.io-col {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
}
.io-col .vid-cell { aspect-ratio: 16 / 9; }
.io-arrow {
  text-align: center;
  color: var(--fg-muted);
  font-size: 1.25rem;
  font-weight: 700;
  line-height: 1;
  margin: 0.15rem 0;
}

@media (max-width: 720px) {
  .io-flow { grid-template-columns: 1fr; gap: 1rem; }
  /* the examples are similar; show just one instead of a long stack to scroll through */
  .io-flow .io-col:nth-child(n + 2) { display: none; }
}

/* ---------- "View more" link + collapsible section ---------- */
.more-link {
  margin: 1.75rem 0 0;
  font-size: 0.98rem;
  font-weight: 600;
}
.more-link a {
  color: var(--accent);
  text-decoration: none;
}
.more-link a:hover { text-decoration: underline; }

.collapsible {
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--bg-alt);
}
.collapsible > summary {
  cursor: pointer;
  list-style: none;
  padding: 1rem 1.25rem;
  font-weight: 600;
  font-size: 1.05rem;
  color: var(--fg);
  display: flex;
  align-items: center;
  gap: 0.6rem;
}
.collapsible > summary::-webkit-details-marker { display: none; }
.collapsible > summary::before {
  content: "\25B6";           /* ▶ */
  font-size: 0.7rem;
  color: var(--fg-muted);
  transition: transform 0.15s ease;
}
.collapsible[open] > summary::before { transform: rotate(90deg); }
.collapsible > summary:hover { color: var(--accent); }

.collapsible-body {
  padding: 0 1.25rem 1.25rem;
}
.collapsible-body .lede { margin-top: 0.5rem; }

/* ---------- BibTeX ---------- */
.bibtex {
  background: var(--bg-alt);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1.1rem 1.25rem;
  overflow-x: auto;
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 0.85rem;
  line-height: 1.55;
  color: var(--fg-soft);
  margin: 0;
}
.bibtex code { font-family: inherit; }

/* ---------- Footer ---------- */
.site-footer {
  border-top: 1px solid var(--border);
  padding: 2.5rem 0 3rem;
  text-align: center;
  color: var(--fg-soft);
  font-size: 0.92rem;
}
.site-footer p { margin: 0.2rem 0; }
.footer-muted { color: var(--fg-muted); font-size: 0.85rem; }