/* ============================================================
   PAPER PROJECT PAGES
   Shared styles for the dedicated, video-first paper pages
   (papers/<slug>/index.html). Inherits color/type tokens from
   the root styles.css — this file only adds new structure:
   hero video, sticky story-nav, narrative sections, inline
   video/figure embeds, stat callouts, dark "moment" bands.
   ============================================================ */

/* fixed-dark palette for dramatic bands — intentionally NOT tied to
   the light/dark theme toggle, so the contrast always reads correctly */
:root {
  --pp-dark-bg: #131110;
  --pp-dark-text: #f3efe8;
  --pp-dark-text-soft: #c9c4ba;
  --pp-dark-line: #2c2926;
}

/* ---------- Sticky chrome (top bar + story nav share one sticky box) ----------
   Both bars live in a single sticky container so the nav can never slide
   under the top bar. Anything that depends on their combined height reads
   it off the element instead of hardcoding a number. */
.pp-stickytop {
  position: sticky; top: 0; z-index: 50;
  background: var(--header-bg);
  backdrop-filter: blur(10px) saturate(1.4);
  -webkit-backdrop-filter: blur(10px) saturate(1.4);
}
.pp-topbar {
  display: flex; align-items: center; justify-content: space-between;
  gap: 1rem;
  padding: .85rem clamp(1rem, 4vw, 2rem);
  border-bottom: 1px solid var(--line);
}
.pp-topbar-back {
  display: inline-flex; align-items: center; gap: .5rem;
  font-size: var(--text-sm); font-weight: 700; color: var(--ink-soft);
}
.pp-topbar-back:hover { color: var(--orange-deep); }
.pp-topbar-back .arrow { color: var(--orange); }
.pp-topbar-actions { display: flex; align-items: center; gap: .6rem; }
.pp-topbar-actions .pp-btn { font-size: var(--text-xs); }

/* ---------- Hero ---------- */
.pp-hero {
  position: relative;
  min-height: min(92vh, 780px);
  display: flex; align-items: flex-end;
  overflow: hidden;
  background: var(--pp-dark-bg);
}
.pp-hero video, .pp-hero .pp-hero-poster {
  position: absolute; inset: 0;
  width: 100%; height: 100%;
  object-fit: cover;
  opacity: .55;
  /* pages can aim the crop at the part of the frame worth showing */
  object-position: var(--pp-poster-pos, center);
}
.pp-hero::after {
  content: ""; position: absolute; inset: 0;
  background: linear-gradient(180deg, rgba(19,17,16,.15) 0%, rgba(19,17,16,.55) 55%, rgba(19,17,16,.92) 100%);
}
.pp-hero-content {
  position: relative; z-index: 2;
  width: 100%; max-width: var(--maxw); margin: 0 auto;
  padding: 6rem clamp(1.25rem, 4vw, 3rem) 3.5rem;
  color: var(--pp-dark-text);
}
.pp-hero-badges { display: flex; flex-wrap: wrap; gap: .5rem; margin-bottom: 1.2rem; }
.pp-badge {
  display: inline-flex; align-items: center; gap: .4rem;
  font-size: var(--text-xs); font-weight: 700; letter-spacing: .08em; text-transform: uppercase;
  padding: .3rem .7rem; border-radius: 999px;
  border: 1px solid rgba(255,255,255,.28);
  background: rgba(255,255,255,.08);
  color: var(--pp-dark-text);
}
.pp-badge.is-orange { background: var(--orange); border-color: var(--orange); color: var(--on-orange); }
.pp-hero-title {
  font-family: var(--mono); font-weight: 700; letter-spacing: -0.01em;
  font-size: clamp(1.9rem, 4.4vw, 3.4rem);
  line-height: 1.12;
  max-width: 22ch;
  margin-bottom: 1rem;
  text-wrap: balance;
}
.pp-hero-subtitle {
  font-size: clamp(1rem, 1.6vw, 1.25rem);
  line-height: 1.55;
  color: var(--pp-dark-text-soft);
  max-width: 62ch;
  margin-bottom: 1.4rem;
}
.pp-hero-meta { font-size: var(--text-sm); color: var(--pp-dark-text-soft); }
.pp-hero-meta b { color: var(--pp-dark-text); font-weight: 700; }
.pp-scrolldown {
  position: absolute; left: 50%; bottom: 1.4rem; z-index: 2;
  transform: translateX(-50%);
  color: var(--pp-dark-text-soft); font-size: var(--text-xs);
  display: flex; flex-direction: column; align-items: center; gap: .35rem;
  letter-spacing: .1em; text-transform: uppercase;
  animation: ppBob 2s ease-in-out infinite;
}
@keyframes ppBob { 0%,100% { transform: translate(-50%, 0); } 50% { transform: translate(-50%, 6px); } }

/* ---------- Story nav (sticky, below topbar) ---------- */
.pp-storynav-wrap {
  border-bottom: 1px solid var(--line);
}
.pp-storynav {
  display: flex; gap: 1.6rem;
  max-width: var(--maxw); margin: 0 auto;
  padding: 0 clamp(1.25rem, 4vw, 3rem);
  overflow-x: auto; scrollbar-width: none;
}
.pp-storynav::-webkit-scrollbar { display: none; }
.pp-storynav a {
  flex-shrink: 0;
  font-size: var(--text-sm); font-weight: 700; color: var(--ink-faint);
  padding: .8rem .1rem; white-space: nowrap;
  border-bottom: 2px solid transparent;
  transition: color .15s ease, border-color .15s ease;
}
.pp-storynav a:hover { color: var(--ink); }
.pp-storynav a.is-active { color: var(--orange-deep); border-color: var(--orange); }

/* ---------- Sections ---------- */
/* scroll-margin keeps a section heading clear of the sticky chrome when
   the browser (rather than our own JS) does the scrolling. */
.pp-section { padding: clamp(3rem, 7vw, 5.5rem) clamp(1.25rem, 4vw, 3rem); scroll-margin-top: 110px; }
.pp-section-inner { max-width: 880px; margin: 0 auto; }
.pp-section--wide .pp-section-inner { max-width: 1100px; }
.pp-section--tint { background: var(--paper); }
.pp-section--dark { background: var(--pp-dark-bg); color: var(--pp-dark-text); border-top: 1px solid var(--pp-dark-line); border-bottom: 1px solid var(--pp-dark-line); }
.pp-section--dark .pp-eyebrow { color: var(--orange); }
.pp-section--dark .pp-section-title { color: var(--pp-dark-text); }
.pp-section--dark .pp-prose p { color: var(--pp-dark-text-soft); }
.pp-section--dark .pp-prose b, .pp-section--dark .pp-prose strong { color: var(--pp-dark-text); }
.pp-section--dark .pp-video, .pp-section--dark .pp-figure img { border-color: var(--pp-dark-line); }
.pp-section--dark .pp-video figcaption, .pp-section--dark .pp-figure figcaption { color: var(--pp-dark-text-soft); }
.pp-section--dark .pp-callout { background: rgba(255,255,255,.05); border-color: var(--pp-dark-line); }
.pp-section--dark .pp-callout b { color: var(--pp-dark-text); }
.pp-section--dark .pp-stat span { color: var(--pp-dark-text-soft); }

.pp-eyebrow {
  display: block; font-size: var(--text-xs); font-weight: 700;
  letter-spacing: .14em; text-transform: uppercase; color: var(--orange-deep);
  margin-bottom: .7rem;
}
.pp-section-title {
  font-family: var(--mono); font-weight: 700; letter-spacing: -0.01em;
  font-size: clamp(1.45rem, 2.6vw, 2.1rem);
  line-height: 1.2;
  margin-bottom: 1.4rem;
  max-width: 26ch;
}
.pp-tldr .pp-section-title { max-width: 34ch; }

.pp-prose p { font-size: 1rem; line-height: 1.85; color: var(--ink-soft); margin-bottom: 1.15rem; }
.pp-prose p:last-child { margin-bottom: 0; }
.pp-prose b, .pp-prose strong { color: var(--ink); }
.pp-prose code {
  font-family: var(--mono); font-size: .88em;
  background: var(--kw-bg); border: 1px solid var(--line);
  padding: .08em .32em; border-radius: 4px; color: var(--ink);
}
.pp-lede { font-size: 1.15rem; line-height: 1.75; color: var(--ink); }

/* ---------- Inline video ---------- */
.pp-video {
  border: 1px solid var(--line-strong); border-radius: var(--radius);
  overflow: hidden; background: #000;
  box-shadow: var(--shadow-md);
}
.pp-video video { display: block; width: 100%; height: auto; }
.pp-video figcaption {
  padding: .85rem 1.1rem;
  font-size: var(--text-xs); line-height: 1.6; color: var(--ink-faint);
  background: var(--white); border-top: 1px solid var(--line);
}
.pp-video figcaption b { color: var(--orange-deep); }
.pp-video-row { display: grid; grid-template-columns: 1fr 1fr; gap: 1.4rem; margin: 1.8rem 0; }
.pp-video-solo { margin: 1.8rem 0; }
.pp-video-solo .pp-video { max-width: 640px; margin: 0 auto; }

/* ---------- Labelled clip gallery ----------
   Each clip carries a tag saying which run it is, so a reader can tell
   a trained PPO policy apart from a collapsing SAC run at a glance. */
.pp-clips { display: grid; gap: 1.6rem; margin: 1.9rem 0; }
.pp-clips.is-two { grid-template-columns: 1fr 1fr; }
.pp-clip {
  margin: 0;
  border: 1px solid var(--line-strong); border-radius: var(--radius);
  overflow: hidden; background: #000;
  box-shadow: var(--shadow-md);
  position: relative;
}
.pp-clip video { display: block; width: 100%; height: auto; }
.pp-clip-tag {
  position: absolute; top: .7rem; left: .7rem; z-index: 2;
  font-size: var(--text-xs); font-weight: 700;
  letter-spacing: .1em; text-transform: uppercase;
  padding: .22rem .6rem; border-radius: 999px;
  background: var(--orange); color: var(--on-orange);
}
.pp-clip figcaption {
  padding: .9rem 1.1rem;
  font-size: var(--text-xs); line-height: 1.65; color: var(--ink-faint);
  background: var(--white); border-top: 1px solid var(--line);
}
.pp-clip figcaption b { color: var(--ink); }
.pp-section--dark .pp-clip { border-color: var(--pp-dark-line); }
.pp-section--dark .pp-clip figcaption {
  background: rgba(255,255,255,.04); border-color: var(--pp-dark-line);
  color: var(--pp-dark-text-soft);
}
.pp-section--dark .pp-clip figcaption b { color: var(--pp-dark-text); }

/* ---------- Figures (still images) ---------- */
.pp-figure { margin: 1.8rem 0; }
.pp-figure img {
  display: block; width: 100%; height: auto;
  background: #fff; padding: .75rem;
  border: 1px solid var(--line-strong); border-radius: var(--radius);
  cursor: zoom-in;
}
.pp-figure figcaption {
  font-size: var(--text-xs); line-height: 1.7; color: var(--ink-faint);
  margin-top: .7rem; padding-left: .85rem; border-left: 2px solid var(--orange-soft);
}
.pp-figure figcaption b { color: var(--orange-deep); }
.pp-figure-row { display: grid; grid-template-columns: 1fr 1fr; gap: 1.4rem; margin: 1.8rem 0; }
.pp-figure-row .pp-figure { margin: 0; }

/* ---------- Callouts / stats ---------- */
.pp-callout {
  border-left: 3px solid var(--orange);
  background: var(--orange-tint);
  padding: 1rem 1.25rem;
  border-radius: 0 10px 10px 0;
  margin: 1.6rem 0;
  font-size: .95rem; line-height: 1.75; color: var(--ink-soft);
}
.pp-callout b { color: var(--ink); }
.pp-stat-row { display: flex; flex-wrap: wrap; gap: 1.6rem; margin: 2rem 0; }
.pp-stat { flex: 1 1 140px; }
.pp-stat b {
  display: block; font-family: var(--mono); font-weight: 700;
  font-size: clamp(1.6rem, 3vw, 2.2rem); color: var(--orange-deep); line-height: 1.1;
}
.pp-stat span { display: block; font-size: var(--text-xs); color: var(--ink-faint); margin-top: .3rem; letter-spacing: .02em; }

/* ---------- Timeline / test log list (for the RL page's experiment walkthrough) ---------- */
.pp-log { margin: 1.8rem 0; display: flex; flex-direction: column; gap: 0; border-top: 1px solid var(--line); }
.pp-log-row { display: grid; grid-template-columns: 90px 110px 1fr; gap: 1rem; padding: .9rem 0; border-bottom: 1px solid var(--line); align-items: baseline; }
.pp-log-row .pp-log-test { font-family: var(--mono); font-weight: 700; color: var(--ink); font-size: var(--text-sm); }
.pp-log-row .pp-log-len { font-family: var(--mono); font-size: var(--text-sm); color: var(--orange-deep); }
.pp-log-row .pp-log-note { font-size: var(--text-sm); color: var(--ink-soft); line-height: 1.6; }
.pp-section--dark .pp-log { border-color: var(--pp-dark-line); }
.pp-section--dark .pp-log-row { border-color: var(--pp-dark-line); }
.pp-section--dark .pp-log-row .pp-log-test { color: var(--pp-dark-text); }
.pp-section--dark .pp-log-row .pp-log-note { color: var(--pp-dark-text-soft); }

/* ---------- Closing / footer CTA ---------- */
.pp-close { text-align: center; }
.pp-close .pp-section-title { max-width: none; }
.pp-close-actions { display: flex; flex-wrap: wrap; gap: .8rem; justify-content: center; margin-top: 1.6rem; }
.pp-btn {
  display: inline-flex; align-items: center; gap: .5rem;
  font-size: var(--text-sm); font-weight: 700;
  padding: .65rem 1.2rem; border-radius: 999px;
  border: 1px solid var(--line-strong); color: var(--ink-soft);
  transition: all .18s ease;
}
.pp-btn:hover { border-color: var(--orange); color: var(--orange-deep); background: var(--orange-tint); }
.pp-btn.is-primary { background: var(--orange); border-color: var(--orange); color: var(--on-orange); }
.pp-btn.is-primary:hover { background: var(--orange-deep); border-color: var(--orange-deep); color: var(--on-orange); }

.pp-refs { max-width: 880px; margin: 0 auto; padding-left: 1.4rem; }
.pp-refs li { font-size: var(--text-xs); line-height: 1.75; color: var(--ink-faint); margin-bottom: .55rem; }
.pp-refs li::marker { color: var(--orange); }

.pp-footer {
  padding: 2.2rem clamp(1.25rem, 4vw, 3rem) 2.6rem;
  border-top: 1px solid var(--line);
  display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 1rem;
  font-size: var(--text-xs); color: var(--ink-faint);
}

/* ---------- Responsive ---------- */
@media (max-width: 760px) {
  .pp-hero { min-height: 78vh; }
  .pp-video-row, .pp-figure-row, .pp-clips.is-two { grid-template-columns: 1fr; }
  .pp-section { scroll-margin-top: 96px; }
  .pp-log-row { grid-template-columns: 70px 90px 1fr; gap: .6rem; }
}
@media (prefers-reduced-motion: reduce) {
  .pp-scrolldown { animation: none; }
}