:root{
  --bg:#0F2439;
  --bg-panel:#15304A;
  --grid-line:rgba(220,234,244,0.055);
  --grid-line-major:rgba(220,234,244,0.10);
  --line:#DCEAF4;
  --line-dim:#7C9BB6;
  --gold:#C9A227;
  --gold-soft:#E7C765;
  --white:#F5F9FC;
  --rule:rgba(220,234,244,0.16);
}
*{box-sizing:border-box;}
html{scroll-behavior:smooth;}
body{
  margin:0;
  background-color:var(--bg);
  background-image:
    linear-gradient(var(--grid-line) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid-line) 1px, transparent 1px),
    linear-gradient(var(--grid-line-major) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid-line-major) 1px, transparent 1px);
  background-size:20px 20px,20px 20px,100px 100px,100px 100px;
  color:var(--line);
  font-family:'IBM Plex Sans',-apple-system,sans-serif;
  font-size:17px;
  line-height:1.65;
  -webkit-font-smoothing:antialiased;
}
.wrap{
  max-width:760px;
  margin:0 auto;
  padding:64px 24px 90px;
}

.crumbs{
  display:flex; flex-wrap:wrap; gap:8px; align-items:center;
  margin:0 0 20px; padding:0;
  font-family:'IBM Plex Mono',monospace;
  font-size:11px; letter-spacing:0.08em; text-transform:uppercase;
  color:var(--line-dim);
}
.crumbs a{
  color:var(--gold-soft); text-decoration:none; border-bottom:1px solid rgba(231,199,101,0.25);
  transition:color 0.15s ease, border-color 0.15s ease;
}
.crumbs a:hover{color:var(--white); border-bottom-color:var(--gold-soft)}
.crumbs span{color:var(--line-dim); opacity:0.9}
.sheet{
  position:relative;
  background:var(--bg-panel);
  border:1px solid var(--rule);
  padding:48px clamp(24px,5vw,64px) 56px;
}
.sheet::before,.sheet::after,
.corner-tl,.corner-br{
  content:'';
  position:absolute;
  width:22px;height:22px;
  border-color:var(--gold);
  border-style:solid;
  opacity:0.85;
}
.sheet::before{ top:-1px; left:-1px; border-width:2px 0 0 2px; }
.sheet::after{ bottom:-1px; right:-1px; border-width:0 2px 2px 0; }

.eyebrow{
  font-family:'IBM Plex Mono',monospace;
  font-size:12px;
  letter-spacing:0.14em;
  text-transform:uppercase;
  color:var(--gold-soft);
  display:flex;
  align-items:center;
  gap:10px;
  margin-bottom:22px;
}
.eyebrow::after{
  content:'';
  flex:1;
  height:1px;
  background:var(--rule);
}
h1{
  font-family:'Fraunces',serif;
  font-style:italic;
  font-weight:600;
  font-size:clamp(34px,5vw,50px);
  line-height:1.08;
  margin:0 0 6px;
  color:var(--white);
}
.subtitle{
  font-family:'IBM Plex Mono',monospace;
  font-size:13px;
  color:var(--line-dim);
  letter-spacing:0.03em;
  margin:0 0 36px;
}
p{ margin:0 0 20px; color:var(--line); }
p.lede{ font-size:19px; color:var(--white); }
a{ color:var(--gold-soft); text-decoration:none; border-bottom:1px solid rgba(231,199,101,0.35); }
a:hover{ border-bottom-color:var(--gold-soft); }
a:focus-visible, button:focus-visible{ outline:2px solid var(--gold-soft); outline-offset:3px; }

blockquote{
  margin:36px 0;
  padding:18px 26px;
  border-left:2px solid var(--gold);
  background:rgba(201,162,39,0.07);
  font-family:'Fraunces',serif;
  font-style:italic;
  font-size:21px;
  color:var(--white);
  line-height:1.5;
}
blockquote cite{
  display:block;
  margin-top:12px;
  font-family:'IBM Plex Mono',monospace;
  font-style:normal;
  font-size:12px;
  letter-spacing:0.06em;
  color:var(--line-dim);
}

.hero-diagram{ width:100%; max-width:340px; display:block; margin:8px auto 36px; }

h2{
  font-family:'Fraunces',serif;
  font-weight:600;
  font-size:22px;
  color:var(--white);
  margin:44px 0 18px;
}

/* Table of contents */
.toc{ list-style:none; margin:0; padding:0; }
.toc li{ border-top:1px solid var(--rule); }
.toc li:last-child{ border-bottom:1px solid var(--rule); }
.toc a{
  display:flex;
  align-items:center;
  gap:18px;
  padding:16px 4px;
  border-bottom:none;
  color:var(--line);
}
.toc a:hover .toc-title{ color:var(--gold-soft); }
.toc a:hover{ background:rgba(220,234,244,0.03); }
.unit-icon{ width:34px; height:34px; flex:none; }
.toc-num{
  font-family:'IBM Plex Mono',monospace;
  font-size:12px;
  color:var(--line-dim);
  width:52px;
  flex:none;
}
.toc-body{ flex:1; min-width:0; }
.toc-title{ font-family:'Fraunces',serif; font-size:17px; color:var(--white); }
.toc-title .opt{ font-family:'IBM Plex Mono',monospace; font-size:11px; color:var(--gold-soft); margin-left:8px; }
.toc-blurb{ font-size:14px; color:var(--line-dim); margin-top:3px; }
.toc-arrow{ font-family:'IBM Plex Mono',monospace; color:var(--gold); flex:none; }

/* Lesson list on unit pages */
.lessons{ list-style:none; margin:0 0 8px; padding:0; }
.lessons li{
  border-top:1px solid var(--rule);
}
.lessons li:last-child{ border-bottom:1px solid var(--rule); }
.lessons a.lesson-row{
  display:flex;
  gap:18px;
  align-items:baseline;
  padding:13px 4px;
  border-bottom:none;
  color:var(--line);
}
.lessons a.lesson-row:hover{ background:rgba(220,234,244,0.03); }
.lessons a.lesson-row:hover .lesson-title{ color:var(--gold-soft); }
.lesson-num{
  font-family:'IBM Plex Mono',monospace;
  font-size:13px;
  color:var(--gold-soft);
  width:44px;
  flex:none;
}
.lesson-title{ flex:1; color:var(--line); }
.lesson-time{
  font-family:'IBM Plex Mono',monospace;
  font-size:11.5px;
  color:var(--line-dim);
  flex:none;
  white-space:nowrap;
}

.review-box{
  margin-top:26px;
  padding:18px 22px;
  border:1px dashed var(--gold);
  background:rgba(201,162,39,0.06);
  display:flex;
  align-items:center;
  gap:14px;
}
.review-box .tag{
  font-family:'IBM Plex Mono',monospace;
  font-size:10.5px;
  letter-spacing:0.08em;
  text-transform:uppercase;
  color:var(--bg);
  background:var(--gold-soft);
  padding:3px 8px;
  flex:none;
}
.review-box .txt{ color:var(--white); font-size:15px; }
.review-box .txt small{ display:block; color:var(--line-dim); font-size:12.5px; margin-top:2px; }

.nav-row{
  margin-top:48px;
  padding-top:22px;
  border-top:1px solid var(--rule);
  display:flex;
  justify-content:space-between;
  gap:16px;
  font-family:'IBM Plex Mono',monospace;
  font-size:13px;
}
.nav-row a{ border-bottom:none; }
.nav-row .center{ text-align:center; }

footer{
  max-width:760px;
  margin:0 auto;
  padding:0 24px 60px;
  font-family:'IBM Plex Mono',monospace;
  font-size:11.5px;
  color:var(--line-dim);
  display:flex;
  justify-content:space-between;
  gap:12px;
}

@media (max-width:600px){
  .wrap{ padding:36px 14px 60px; }
  .sheet{ padding:34px 20px 40px; }
  .toc a{ gap:12px; }
  .toc-num{ width:36px; }
}