/* ============================================================
   Design tokens — tweak these to rebrand the whole page
   ============================================================ */
:root {
  --accent: #2563eb;
  --accent-dark: #1d4ed8;
  --text: #1a1a1a;
  --text-muted: #555;
  --bg: #ffffff;
  --bg-alt: #f6f7f9;
  --border: #e5e7eb;
  --max-width: 1080px;
  --narrow-width: 760px;
  --radius: 10px;
  font-size: 16px;
}

@media (prefers-color-scheme: dark) {
  :root {
    --text: #e8e8e8;
    --text-muted: #a0a0a0;
    --bg: #0f1115;
    --bg-alt: #171a21;
    --border: #2a2e37;
  }
}

/* ============================================================
   Base
   ============================================================ */
* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  color: var(--text);
  background: var(--bg);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

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

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

h2 {
  font-size: 1.6rem;
  font-weight: 700;
  text-align: center;
  margin: 0 0 1rem;
}

/* Subsection heading (e.g. parts within Experiments). */
.subsection {
  font-size: 1.25rem;
  font-weight: 600;
  text-align: center;
  margin: 2.5rem 0 0.75rem;
}

/* ============================================================
   Accordion (collapsible sub-sections, e.g. Experiments)
   ============================================================ */
.accordion {
  max-width: 980px;
  margin: 0 auto;
}
.accordion-item {
  border: 1px solid var(--border);
  border-radius: var(--radius);
  margin-bottom: 0.85rem;
  overflow: hidden;
  background: var(--bg-alt);
}
.accordion-header {
  list-style: none;            /* hide default disclosure triangle */
  cursor: pointer;
  padding: 1rem 1.25rem;
  font-size: 1.2rem;
  font-weight: 600;
  color: var(--text);
  display: flex;
  align-items: center;
  justify-content: space-between;
  user-select: none;
}
.accordion-header::-webkit-details-marker { display: none; }
.accordion-header::after {
  content: "+";
  font-size: 1.4rem;
  font-weight: 400;
  color: var(--accent);
  transition: transform 0.2s ease;
}
.accordion-item[open] .accordion-header::after {
  content: "\2212"; /* minus sign */
}
.accordion-header:hover { color: var(--accent); }
.accordion-body {
  padding: 0.25rem 1.25rem 1.25rem;
  background: var(--bg);
}
.accordion-body .section-intro { margin-top: 1rem; }

/* Collapsible takeaway: the callout itself is the clickable summary. */
.takeaway-item {
  max-width: 820px;
  margin: 1.25rem auto;
}
.takeaway {
  padding: 0.85rem 1.1rem;
  background: var(--bg-alt);
  border-left: 4px solid var(--accent);
  border-radius: 6px;
  color: var(--text);
}
.takeaway strong { color: var(--accent); }

/* summary styling (when a .takeaway is used as a <details> summary) */
summary.takeaway {
  cursor: pointer;
  list-style: none;
  display: flex;
  align-items: center;
  justify-content: space-between;
  user-select: none;
}
summary.takeaway::-webkit-details-marker { display: none; }
summary.takeaway::after {
  content: "+";
  color: var(--accent);
  font-size: 1.3rem;
  line-height: 1;
  margin-left: 1rem;
}
.takeaway-item[open] > summary.takeaway::after { content: "\2212"; }

.takeaway-detail {
  margin: 0.6rem 0 0;
  padding: 0 0.25rem;
  text-align: justify;
  color: var(--text-muted);
}

/* ============================================================
   Hero
   ============================================================ */
.hero {
  background: var(--bg-alt);
  border-bottom: 1px solid var(--border);
  padding: 4rem 0 3rem;
  text-align: center;
}

.title {
  font-size: clamp(1.8rem, 4vw, 3rem);
  font-weight: 700;
  line-height: 1.15;
  margin: 0 0 0.75rem;
}

.subtitle {
  font-size: 1.15rem;
  color: var(--text-muted);
  max-width: 640px;
  margin: 0 auto 2rem;
}

.authors {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 0.25rem 1.25rem;
  font-size: 1.1rem;
  margin-bottom: 0.5rem;
}
.author sup { color: var(--text-muted); }

.affiliations {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 0.25rem 1.5rem;
  color: var(--text-muted);
  font-size: 0.95rem;
  margin-bottom: 0.5rem;
}

.venue {
  font-weight: 600;
  color: var(--accent);
  margin-bottom: 2rem;
}

/* ============================================================
   Buttons
   ============================================================ */
.buttons {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 0.75rem;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.6rem 1.25rem;
  background: var(--text);
  color: var(--bg);
  border-radius: 999px;
  font-weight: 500;
  font-size: 0.95rem;
  transition: transform 0.15s ease, opacity 0.15s ease;
}
.btn:hover { transform: translateY(-2px); opacity: 0.9; text-decoration: none; }
.btn .icon { font-size: 1rem; }

/* ============================================================
   Sections
   ============================================================ */
.section {
  padding: 3rem 0;
  border-bottom: 1px solid var(--border);
}
.section:last-of-type { border-bottom: none; }

figure { margin: 1.5rem 0; text-align: center; }
figure img {
  max-width: 100%;
  height: auto;
  border-radius: var(--radius);
  border: 1px solid var(--border);
}

/* Standalone section figures (Taxonomy, Pipeline, Experiments, …): cap the
   width and center, so the figures are smaller and all line up to the same
   width. Carousel / video-pair figures are nested deeper and unaffected. */
.container > figure {
  max-width: 860px;
  margin-left: auto;
  margin-right: auto;
}

/* Smaller, centered figure (e.g. some takeaway figures). */
.fig-narrow {
  max-width: 600px;
  margin-left: auto;
  margin-right: auto;
}
figcaption {
  margin-top: 0.75rem;
  font-size: 0.9rem;
  color: var(--text-muted);
}

.teaser img { border: none; }

/* Teaser caption: normal left-aligned body text, not the centered figcaption. */
.teaser-caption {
  text-align: justify;
  font-size: 1rem;
  line-height: 1.35;
  color: #777;
  margin-top: 0.25rem;   /* hug the teaser image */
  margin-bottom: 1.5rem; /* keep more space before the abstract */
}

.section-lead {
  text-align: center;
  color: var(--text-muted);
  max-width: 640px;
  margin: 0 auto 2rem;
}

/* Justify body text so both edges are flush (e.g. the abstract). */
.justify {
  text-align: justify;
  text-justify: inter-word;
  hyphens: auto;
}

/* A paragraph of intro text inside a wide section: centered block, readable
   width, justified (not center-aligned like a one-line .section-lead). */
.section-intro {
  max-width: 820px;
  margin: 0 auto 2rem;
  text-align: justify;
  hyphens: auto;
  color: var(--text-muted);
}

/* Lettered list (a, b, c) sharing the centered, readable width of .section-intro. */
.composition-list {
  max-width: 820px;
  margin: 0 auto 2rem;
  padding-left: 1.5rem;
  list-style: lower-alpha;
  color: var(--text-muted);
  text-align: justify;
}
.composition-list li {
  margin-bottom: 0.6rem;
  padding-left: 0.35rem;
}
.composition-list li::marker {
  font-weight: 700;
  color: var(--text);
}

/* Numbered list (1, 2) with nested sub-items, e.g. Spatial Reasoning Design. */
.spatial-list {
  max-width: 820px;
  margin: 0 auto 2rem;
  padding-left: 1.5rem;
  list-style: decimal;
  color: var(--text-muted);
  text-align: justify;
}
.spatial-list > li {
  margin-bottom: 0.6rem;
  padding-left: 0.35rem;
}
.spatial-list > li::marker {
  font-weight: 700;
  color: var(--text);
}
.spatial-list ul {
  list-style: disc;
  margin-top: 0.5rem;
  padding-left: 1.5rem;
}
.spatial-list ul li {
  margin-bottom: 0.35rem;
}

/* Three camera-viewpoint images side by side, each with a caption. */
.viewpoint-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1.25rem;
  margin: 1rem 0 0.5rem;
}

/* The viewpoint example-group carousel lives inside the narrow 820px list
   column; break it out to a wider, page-centered block so the three photos
   render larger. Capped to the viewport to avoid horizontal scroll. */
.viewpoint-carousel {
  position: relative;
  left: 50%;
  transform: translateX(-50%);
  width: min(1080px, 95vw);
  margin: 1.5rem 0;
}
.viewpoint-carousel .viewpoint-grid {
  gap: 1rem;
  margin: 0;
}
.viewpoint-carousel + .carousel-counter {
  position: relative;
  left: 50%;
  transform: translateX(-50%);
  width: min(1080px, 95vw);
}
.viewpoint-cell { margin: 0; text-align: center; }
.viewpoint-cell img {
  width: 100%;
  height: auto;
  border-radius: var(--radius);
  border: 1px solid var(--border);
}
.viewpoint-cell figcaption {
  margin-top: 0.5rem;
  font-weight: 600;
  color: var(--text);
}

@media (max-width: 640px) {
  .viewpoint-grid { grid-template-columns: 1fr; }
}

/* ============================================================
   Motivation example — instruction + side-by-side videos
   ============================================================ */
.example {
  margin: 0 auto 2.5rem;
  max-width: 980px;
}
.example:last-child { margin-bottom: 0; }

.instruction {
  text-align: center;
  font-size: 1.1rem;
  margin: 0 0 1rem;
}
.instruction-label {
  font-weight: 700;
  color: var(--accent);
  margin-right: 0.35rem;
}

/* Larger instruction + video captions in the Motivating Example section. */
.example .instruction { font-size: 1.45rem; }
.example .video-cell figcaption { font-size: 1.2rem; }

/* Lock both Motivating Example videos to the same box so they match and align
   (the two clips have slightly different aspect ratios otherwise). */
.example .video-pair .bare-video {
  aspect-ratio: 9 / 10;
  height: auto;
  object-fit: cover;
}

/* Two videos side by side with a gap in the middle */
.video-pair {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.5rem;
}

.video-cell { margin: 0; text-align: center; }
.video-cell figcaption {
  margin-top: 0.6rem;
  font-weight: 600;
  color: var(--text);
}

/* Plain (non-embedded) video element */
.bare-video {
  width: 100%;
  height: auto;
  display: block;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  background: #000;
}

/* Overview video: lock the 16:9 box so it never resizes on play, and show the
   poster frame fully (contain) rather than cropping it. */
.overview-video {
  aspect-ratio: 16 / 9;
  height: auto;
  object-fit: contain;
  /* Break out of the narrow (760px) container to a larger, page-centered box.
     Capped to the viewport so it never causes horizontal scroll. */
  position: relative;
  left: 50%;
  transform: translateX(-50%);
  width: min(1000px, 95vw);
  max-width: none;
}

/* Task examples — one video + one image side by side */
.media-pair {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.5rem;
  align-items: center;
}
.media-cell { margin: 0; text-align: center; }
.media-cell img {
  width: 100%;
  height: auto;
  border-radius: var(--radius);
  border: 1px solid var(--border);
}

/* The human video (16:9) and executable-task image (square) have different
   aspect ratios; lock both to the same 16:9 box so the pair lines up. */
.media-pair .bare-video,
.media-pair img {
  aspect-ratio: 16 / 9;
  height: auto;
  object-fit: contain;
}

/* ============================================================
   Task examples — single-slide carousel with left/right arrows
   ============================================================ */
.carousel {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}
.carousel-track {
  flex: 1;
  min-width: 0;
}
.carousel-slide { display: none; }
.carousel-slide.is-active { display: block; }

.carousel-arrow {
  flex: 0 0 auto;
  width: 44px;
  height: 44px;
  font-size: 1.6rem;
  line-height: 1;
  color: var(--text);
  background: var(--bg-alt);
  border: 1px solid var(--border);
  border-radius: 999px;
  cursor: pointer;
  transition: background 0.15s ease, color 0.15s ease, border-color 0.15s ease;
}
.carousel-arrow:hover {
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
}

.carousel-caption {
  text-align: center;
  margin-top: 0.5rem;
}

/* Caption label style, matching the "Human Video" caption in Motivating Example
   (see .example .video-cell figcaption). Used by Taxonomy Overview and the
   "Examples in WatchAct" carousel caption. */
.caption-label,
.carousel-caption {
  font-size: 1.2rem;
  font-weight: 600;
  color: var(--text);
}

.carousel-counter {
  text-align: center;
  color: var(--text-muted);
  font-size: 0.9rem;
  margin-top: 1rem;
}

/* Simulation videos have mismatched aspect ratios (16:9 vs 1:1). Lock each
   cell to an identical 16:9 box and letterbox the contents so the two videos
   line up neatly. Scoped to the Simulation panel only. */
[data-rollout-panel="sim"] .video-pair .bare-video {
  aspect-ratio: 16 / 9;
  height: auto;
  object-fit: contain;
}

/* ============================================================
   Rollout demos — tabbed examples
   ============================================================ */
.rollout-tabs {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 0.5rem;
  margin-bottom: 1.75rem;
}
.rollout-tab {
  padding: 0.5rem 1.1rem;
  font-size: 0.95rem;
  font-weight: 500;
  color: var(--text);
  background: var(--bg-alt);
  border: 1px solid var(--border);
  border-radius: 999px;
  cursor: pointer;
  transition: background 0.15s ease, color 0.15s ease, border-color 0.15s ease;
}
.rollout-tab:hover { border-color: var(--accent); }
.rollout-tab.is-active {
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
}

.rollout-panel { display: none; }
.rollout-panel.is-active { display: block; }

/* Success / failure highlight in rollout captions. */
.result-success { color: #1a9e4b; font-weight: 700; }
.result-fail { color: #d83a3a; font-weight: 700; }

/* Per-example analysis text below the videos in each rollout slide. */
.rollout-analysis {
  max-width: 820px;
  margin: 1.25rem auto 0;
  text-align: justify;
  color: var(--text-muted);
}

/* Stack video / media pairs on narrow screens */
@media (max-width: 640px) {
  .video-pair,
  .media-pair { grid-template-columns: 1fr; }
}

/* ============================================================
   Responsive video embed (16:9)
   ============================================================ */
.video-wrap {
  position: relative;
  width: 100%;
  padding-top: 56.25%;
  border-radius: var(--radius);
  overflow: hidden;
}
.video-wrap iframe {
  position: absolute;
  top: 0; left: 0;
  width: 100%; height: 100%;
  border: 0;
}

/* ============================================================
   BibTeX block
   ============================================================ */
.bibtex {
  position: relative;
  background: var(--bg-alt);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1rem 1.25rem;
  text-align: left;
}
.bibtex pre {
  margin: 0;
  overflow-x: auto;
  font-size: 0.85rem;
  line-height: 1.5;
}
.copy-btn {
  position: absolute;
  top: 0.75rem;
  right: 0.75rem;
  padding: 0.3rem 0.8rem;
  font-size: 0.8rem;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text);
  border-radius: 6px;
  cursor: pointer;
  transition: background 0.15s ease;
}
.copy-btn:hover { background: var(--accent); color: #fff; border-color: var(--accent); }

/* ============================================================
   Footer
   ============================================================ */
.footer {
  padding: 2.5rem 0;
  text-align: center;
  font-size: 0.85rem;
  color: var(--text-muted);
  background: var(--bg-alt);
}
.footer p { margin: 0.4rem 0; }