/* =========================================================================
   Roadmap to Diffusion Processes — shared stylesheet
   Clean, minimal, academically appropriate. One accent: deep teal.
   ========================================================================= */

:root{
  --paper:#FBFBF8;
  --surface:#FFFFFF;
  --ink:#1B2024;
  --ink-soft:#4C545E;
  --ink-faint:#828A93;
  --line:#E5E4DC;
  --line-strong:#D5D4C9;
  --accent:#0E6E64;        /* deep teal */
  --accent-dark:#0A4F48;
  --accent-tint:#E8F1EF;
  --placeholder:#9AA0A6;
  --focus:#0E6E64;

  --serif:"Source Serif 4", Georgia, "Times New Roman", serif;
  --ui:"Inter", system-ui, -apple-system, "Segoe UI", Helvetica, Arial, sans-serif;

  --measure:42rem;
  --maxw:1140px;
  --radius:6px;
}

*{box-sizing:border-box;}
html{scroll-behavior:smooth;}
body{
  margin:0;
  background:var(--paper);
  color:var(--ink);
  font-family:var(--serif);
  font-size:18px;
  line-height:1.65;
  -webkit-font-smoothing:antialiased;
  text-rendering:optimizeLegibility;
}
::selection{background:var(--accent-tint);}

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

:focus-visible{outline:2px solid var(--focus);outline-offset:2px;border-radius:3px;}

.skip-link{
  position:absolute;left:-9999px;top:0;
  background:var(--accent);color:#fff;font-family:var(--ui);font-size:.85rem;
  padding:.6rem 1rem;border-radius:0 0 var(--radius) 0;z-index:100;
}
.skip-link:focus{left:0;text-decoration:none;}

/* ---------------------------------------------------------------- header */
.site-header{
  background:var(--surface);
  border-bottom:1px solid var(--line);
  position:sticky;top:0;z-index:50;
}
.header-inner{
  max-width:var(--maxw);margin:0 auto;padding:.85rem 1.5rem;
  display:flex;align-items:center;justify-content:space-between;gap:1rem;
}
.brand{
  display:flex;align-items:center;gap:.6rem;
  font-family:var(--ui);font-weight:600;font-size:.98rem;letter-spacing:-.01em;
  color:var(--ink);
}
.brand:hover{text-decoration:none;color:var(--ink);}
.brand-mark{
  width:13px;height:13px;border-radius:50%;
  background:var(--accent);
  box-shadow:0 0 0 3px var(--accent-tint);
  flex:0 0 auto;
}
.site-nav{display:flex;align-items:center;gap:1.4rem;font-family:var(--ui);font-size:.82rem;}
.nav-link,.nav-back{
  font-family:var(--ui);color:var(--ink-soft);font-weight:500;letter-spacing:.01em;
}
.nav-link:hover,.nav-back:hover{color:var(--accent);text-decoration:none;}
.nav-back{font-weight:600;color:var(--accent);}
@media(max-width:560px){
  .brand-text{font-size:.86rem;}
  .nav-link{display:none;}
}

/* ---------------------------------------------------------------- hero */
.hero{
  background:linear-gradient(180deg,var(--surface),var(--paper));
  border-bottom:1px solid var(--line);
}
.hero-inner{max-width:var(--maxw);margin:0 auto;padding:4.5rem 1.5rem 3.5rem;}
.eyebrow{
  font-family:var(--ui);font-size:.74rem;font-weight:600;letter-spacing:.16em;
  text-transform:uppercase;color:var(--accent);margin:0 0 1rem;
}
.hero-title{
  font-family:var(--serif);font-weight:700;font-size:clamp(2.1rem,5vw,3.4rem);
  line-height:1.08;letter-spacing:-.02em;margin:0 0 1rem;max-width:18ch;
}
.hero-tagline{
  font-size:clamp(1.05rem,2.2vw,1.3rem);color:var(--ink-soft);margin:0;max-width:48ch;
  font-style:italic;
}

/* ---------------------------------------------------------------- sections */
.section{border-bottom:1px solid var(--line);}
.section-inner{max-width:var(--maxw);margin:0 auto;padding:3rem 1.5rem;}
.section-title{
  font-family:var(--serif);font-weight:600;font-size:1.5rem;letter-spacing:-.01em;
  margin:0 0 1rem;
}
.section-lede{color:var(--ink-soft);max-width:var(--measure);margin:0 0 2rem;}
.section-overview .placeholder{max-width:var(--measure);}

.placeholder{
  font-family:var(--ui);font-size:.92rem;color:var(--placeholder);
  background:var(--surface);border:1px dashed var(--line-strong);border-radius:var(--radius);
  padding:1rem 1.1rem;margin:0;
}

/* ---------------------------------------------------------------- card grid */
.concept-grid{
  list-style:none;margin:0;padding:0;
  display:grid;grid-template-columns:repeat(auto-fill,minmax(248px,1fr));gap:1rem;
}
.concept-card{margin:0;}
.card-link{
  display:flex;flex-direction:column;height:100%;
  background:var(--surface);border:1px solid var(--line);border-top:3px solid var(--line);
  border-radius:var(--radius);padding:1.2rem 1.2rem 1.1rem;
  color:var(--ink);transition:border-color .18s ease, box-shadow .18s ease, transform .18s ease;
}
.card-link:hover{
  text-decoration:none;color:var(--ink);
  border-top-color:var(--accent);border-color:var(--line-strong);
  box-shadow:0 6px 22px -14px rgba(14,110,100,.5);
  transform:translateY(-2px);
}
.card-num{
  font-family:var(--ui);font-size:.74rem;font-weight:600;letter-spacing:.1em;
  color:var(--accent);margin-bottom:.5rem;
}
.card-name{
  font-family:var(--serif);font-weight:600;font-size:1.16rem;line-height:1.25;
  letter-spacing:-.01em;margin-bottom:.4rem;
}
.card-teaser{
  font-family:var(--ui);font-size:.86rem;color:var(--placeholder);line-height:1.45;
  flex:1 1 auto;
}
.card-cue{
  font-family:var(--ui);font-size:.74rem;font-weight:600;color:var(--ink-faint);
  margin-top:1rem;letter-spacing:.02em;
}
.card-link:hover .card-cue{color:var(--accent);}

/* ---------------------------------------------------------------- concept page */
.concept-main{background:var(--paper);}
.concept{max-width:var(--measure);margin:0 auto;padding:3rem 1.5rem 2rem;}
.concept-head{margin-bottom:2.4rem;padding-bottom:1.6rem;border-bottom:1px solid var(--line);}
.concept-kicker{
  font-family:var(--ui);font-size:.76rem;font-weight:600;letter-spacing:.12em;
  text-transform:uppercase;color:var(--ink-faint);margin:0 0 .7rem;
  display:flex;align-items:center;gap:.6rem;
}
.concept-num{
  font-family:var(--ui);color:var(--accent);background:var(--accent-tint);
  border-radius:4px;padding:.1rem .45rem;font-size:.72rem;
}
.concept-title{
  font-family:var(--serif);font-weight:700;font-size:clamp(1.9rem,4.5vw,2.7rem);
  line-height:1.12;letter-spacing:-.02em;margin:0;
}
.concept-section{margin:2.2rem 0;}
.concept-section-title{
  font-family:var(--serif);font-weight:600;font-size:1.3rem;letter-spacing:-.01em;
  margin:0 0 .8rem;padding-top:.4rem;
}

/* sibling links */
.sibling-links{
  list-style:none;margin:1rem 0 0;padding:0;
  display:grid;grid-template-columns:repeat(auto-fill,minmax(210px,1fr));gap:.4rem .9rem;
}
.sibling-links li{margin:0;}
.sibling-link{
  font-family:var(--ui);font-size:.9rem;color:var(--accent);
  display:inline-block;padding:.2rem 0;border-bottom:1px solid transparent;
}
.sibling-link:hover{text-decoration:none;border-bottom-color:var(--accent);}

/* prev / next pager */
.concept-pager{
  display:flex;justify-content:space-between;gap:1rem;
  margin:3rem 0 1.5rem;padding-top:1.6rem;border-top:1px solid var(--line);
}
.pager-link{
  display:flex;flex-direction:column;gap:.2rem;max-width:48%;
  font-family:var(--ui);
}
.pager-prev{align-items:flex-start;text-align:left;}
.pager-next{align-items:flex-end;text-align:right;margin-left:auto;}
.pager-empty{flex:1;}
.pager-dir{font-size:.74rem;font-weight:600;letter-spacing:.06em;color:var(--ink-faint);}
.pager-name{font-size:.95rem;font-weight:600;color:var(--accent);}
.pager-link:hover{text-decoration:none;}
.pager-link:hover .pager-name{color:var(--accent-dark);}

.concept-return{margin:1.5rem 0 0;font-family:var(--ui);}

/* ---------------------------------------------------------------- footer */
.site-footer{background:var(--surface);border-top:1px solid var(--line);}
.footer-inner{max-width:var(--maxw);margin:0 auto;padding:2.4rem 1.5rem;font-family:var(--ui);}
.footer-title{font-weight:600;font-size:.95rem;color:var(--ink);margin:0 0 .3rem;}
.footer-note{font-size:.86rem;color:var(--ink-faint);margin:0;}

/* ---------------------------------------------------------------- motion */
@media(prefers-reduced-motion:reduce){
  *{transition:none !important;scroll-behavior:auto !important;}
  .card-link:hover{transform:none;}
}

/* ---------------------------------------------------------------- overview prose */
.prose{max-width:var(--measure);}
.prose p{margin:0 0 1.25rem;}
.prose p:first-child{font-size:1.12rem;color:var(--ink);}
.prose p:last-child{margin-bottom:0;}

/* ---------------------------------------------------------------- overview animation */
.diffusion-figure{
  margin:0 0 2rem;
}
.diffusion-figure canvas{
  display:block;width:100%;height:260px;
  background:var(--surface);
  border:1px solid var(--line);
  border-radius:var(--radius);
}
.diffusion-controls{
  display:flex;flex-wrap:wrap;align-items:center;gap:1.1rem;
  margin-top:.7rem;font-family:var(--ui);font-size:.84rem;
}
.dc-item{display:flex;align-items:center;gap:.5rem;color:var(--ink-soft);}
.dc-item label{font-weight:600;color:var(--ink);white-space:nowrap;}
.dc-item input[type=range]{width:128px;accent-color:var(--accent);cursor:pointer;}
.dc-item output{
  font-variant-numeric:tabular-nums;color:var(--accent);font-weight:600;
  min-width:2.6em;
}
.diffusion-controls button{
  font:inherit;font-weight:600;color:var(--accent);background:transparent;
  border:1px solid var(--line-strong);border-radius:6px;padding:.32rem .8rem;cursor:pointer;
}
.diffusion-controls button:hover{background:var(--accent-tint);border-color:var(--accent);}
.diffusion-caption{
  font-family:var(--ui);font-size:.82rem;line-height:1.45;color:var(--ink-faint);
  margin-top:.7rem;max-width:var(--measure);
}
@media(max-width:560px){
  .diffusion-figure canvas{height:200px;}
  .dc-item input[type=range]{width:96px;}
}

/* ---------------------------------------------------------------- concept tutorial body */
.tutorial{font-size:1.02rem;line-height:1.7;}
.tutorial h2{
  font-family:var(--serif);font-weight:600;font-size:1.5rem;letter-spacing:-.01em;
  margin:2.6rem 0 .9rem;padding-top:1.4rem;border-top:1px solid var(--line);
}
.tutorial > h2:first-child{border-top:0;padding-top:0;margin-top:.5rem;}
.tutorial h3{
  font-family:var(--serif);font-weight:600;font-size:1.18rem;letter-spacing:-.005em;
  margin:1.8rem 0 .6rem;color:var(--ink);
}
.tutorial p{margin:0 0 1.1rem;}
.tutorial a{color:var(--accent);}
.tutorial strong{font-weight:600;color:var(--ink);}
/* display math: let wide equations scroll instead of overflowing */
.tutorial .katex-display{overflow-x:auto;overflow-y:hidden;padding:.4rem 0;margin:1.1rem 0;}
.tutorial .katex{font-size:1.02em;}
/* pitfalls / callout list */
.tutorial .callout-list{
  list-style:none;margin:1.2rem 0 0;padding:0;
}
.tutorial .callout-list li{
  background:var(--accent-tint);
  border-left:3px solid var(--accent);
  border-radius:6px;
  padding:.85rem 1.1rem;
  margin:0 0 .8rem;
  font-size:.97rem;line-height:1.6;
}
.tutorial .callout-list li strong{color:var(--accent-dark);}