/* ===== CSS Variables & Reset ===== */
:root {
  --bg: #fbfaf7;
  --bg-elevated: #ffffff;
  --ink: #15212e;
  --ink-soft: #3a4a5c;
  --ink-muted: #6b7785;
  --rule: #e3e0d8;
  --upstream: #1f3a52;
  --midmarket: #4a7396;
  --downstream: #7aa6cc;
  --feedback: #16a085;
  --accent: #c8392c;
  --gold: #d4a843;
  --font-serif: 'Newsreader', Georgia, serif;
  --font-sans: 'Inter', system-ui, sans-serif;
  --font-mono: 'JetBrains Mono', monospace;
  --max-w: 920px;
  --nav-h: 52px;
  --rail-w: 160px;
}
*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
html{scroll-behavior:smooth;-webkit-font-smoothing:antialiased}
body{
  font-family:var(--font-serif);
  font-size:17px;
  line-height:1.75;
  color:var(--ink);
  background:var(--bg);
}

/* ===== Navigation ===== */
.nav-bar{
  position:fixed;top:0;left:0;right:0;z-index:100;
  height:var(--nav-h);
  background:rgba(251,250,247,0.92);
  backdrop-filter:blur(12px);
  border-bottom:1px solid var(--rule);
  display:flex;align-items:center;
}
.nav-inner{
  width:100%;max-width:var(--max-w);margin:0 auto;
  padding:0 24px;
  display:flex;align-items:center;justify-content:space-between;
}
.nav-paper{font-family:var(--font-sans);font-weight:600;font-size:14px;color:var(--ink)}
.nav-sub{font-family:var(--font-sans);font-size:11px;color:var(--ink-muted);margin-left:12px}
.nav-progress{
  width:120px;height:3px;background:var(--rule);border-radius:2px;overflow:hidden;
}
.nav-progress-fill{height:100%;width:0%;background:var(--accent);transition:width .15s}

/* ===== Chapter Rail ===== */
.chapter-rail{
  position:fixed;left:24px;top:50%;transform:translateY(-50%);z-index:90;
  list-style:none;
}
.chapter-rail ol{list-style:none;padding:0;margin:0}
.chapter-rail li{
  display:flex;align-items:center;gap:8px;
  margin-bottom:14px;cursor:pointer;
  transition:all .2s;
}
.chapter-rail .dot{
  width:8px;height:8px;border-radius:50%;
  background:var(--rule);flex-shrink:0;
  transition:all .25s;
}
.chapter-rail li.active .dot{background:var(--accent);transform:scale(1.4)}
.chapter-rail .label{
  font-family:var(--font-sans);font-size:11px;color:var(--ink-muted);
  white-space:nowrap;opacity:0;transform:translateX(-6px);
  transition:all .2s;
}
.chapter-rail li:hover .label,
.chapter-rail li.active .label{opacity:1;transform:translateX(0)}

@media(max-width:1100px){
  .chapter-rail{display:none}
}

/* ===== Chapters ===== */
.chapter{
  max-width:var(--max-w);margin:0 auto;
  padding:7rem 24px 3rem;
}
.chapter+.chapter{border-top:1px solid var(--rule)}

/* Cover */
.cover{padding-top:8rem;text-align:center}
.cover-inner{max-width:720px;margin:0 auto}
.cover-eyebrow{
  font-family:var(--font-sans);font-size:12px;font-weight:600;
  letter-spacing:.12em;text-transform:uppercase;color:var(--accent);
  margin-bottom:16px;
}
.cover-title{
  font-size:clamp(2rem,5vw,3.2rem);font-weight:700;
  line-height:1.15;margin-bottom:12px;
}
.cover-title em{color:var(--accent);font-style:italic}
.cover-subtitle{
  font-family:var(--font-sans);font-size:15px;color:var(--ink-soft);
  margin-bottom:24px;
}
.cover-byline{
  font-family:var(--font-sans);font-size:13px;color:var(--ink-muted);
  margin-bottom:40px;line-height:1.6;
}
.cover-byline .muted{color:var(--ink-muted)}

/* Cover Abstract */
.cover-abstract{
  text-align:left;
  background:var(--bg);
  border-left:3px solid var(--gold);
  padding:24px 28px;
  margin-bottom:48px;
  border-radius:0 6px 6px 0;
}
.cover-abstract-label{
  font-family:var(--font-sans);font-size:11px;font-weight:600;
  letter-spacing:.1em;text-transform:uppercase;color:var(--gold);
  margin-bottom:12px;
}
.cover-abstract p{margin-bottom:12px}
.cover-abstract p:last-child{margin-bottom:0}

/* Cover Pillars */
.cover-pillars{
  display:grid;grid-template-columns:repeat(3,1fr);gap:16px;
  text-align:left;margin-bottom:48px;
}
.pillar{
  background:var(--bg-elevated);
  border:1px solid var(--rule);
  border-radius:8px;
  padding:20px;
}
.pillar-num{
  font-family:var(--font-serif);font-size:28px;font-weight:700;
  color:var(--accent);margin-bottom:6px;
}
.pillar-title{
  font-family:var(--font-sans);font-size:13px;font-weight:600;
  color:var(--upstream);margin-bottom:8px;
}
.pillar-text{
  font-size:13px;line-height:1.6;color:var(--ink-soft);
}

@media(max-width:700px){
  .cover-pillars{grid-template-columns:1fr}
}

/* Chapter Anatomy */
.ch-eyebrow{
  font-family:var(--font-sans);font-size:11px;font-weight:600;
  letter-spacing:.12em;text-transform:uppercase;color:var(--accent);
  margin-bottom:8px;
}
.ch-headline{
  font-size:clamp(1.6rem,3.5vw,2.4rem);font-weight:700;
  line-height:1.2;margin-bottom:16px;
}
.ch-lede{
  font-size:18px;line-height:1.7;color:var(--ink-soft);
  margin-bottom:28px;
}

/* Plain English Card */
.plain-card{
  background:var(--bg);
  border-left:3px solid var(--gold);
  padding:20px 24px;
  margin-bottom:32px;
  border-radius:0 6px 6px 0;
}
.plain-label{
  font-family:var(--font-sans);font-size:11px;font-weight:600;
  letter-spacing:.1em;text-transform:uppercase;color:var(--gold);
  margin-bottom:10px;
}
.plain-card p{margin-bottom:10px;font-size:15px;line-height:1.7}
.plain-card p:last-child{margin-bottom:0}

/* Equation Block */
.equation-block{
  background:var(--bg-elevated);
  border:1px solid var(--rule);
  border-radius:8px;
  padding:20px 24px;
  margin:24px 0;
  overflow-x:auto;
}
.equation-block .eq-label{
  font-family:var(--font-sans);font-size:11px;color:var(--ink-muted);
  margin-bottom:8px;
}

/* Interactive Section */
.interactive-section{
  margin:32px 0;
}
.slider-group{
  display:grid;grid-template-columns:repeat(auto-fit,minmax(200px,1fr));gap:12px 20px;
  margin-bottom:16px;
}
.slider-item{
  display:flex;flex-direction:column;gap:4px;
}
.slider-item label{
  font-family:var(--font-sans);font-size:12px;font-weight:500;
  color:var(--ink-soft);display:flex;justify-content:space-between;
}
.slider-item label .val{
  font-family:var(--font-mono);font-size:12px;color:var(--accent);
}
input[type="range"]{
  -webkit-appearance:none;width:100%;height:6px;
  background:var(--rule);border-radius:3px;outline:none;
}
input[type="range"]::-webkit-slider-thumb{
  -webkit-appearance:none;width:16px;height:16px;
  background:var(--accent);border-radius:50%;cursor:pointer;
}
.chart-wrap{
  border:1px solid var(--rule);border-radius:8px;
  overflow:hidden;margin-bottom:12px;
  background:var(--bg-elevated);
}
.chart-grid{
  display:grid;grid-template-columns:1fr 1fr;gap:12px;
}
@media(max-width:640px){
  .chart-grid{grid-template-columns:1fr}
}
.hint{
  font-family:var(--font-sans);font-size:11px;color:var(--ink-muted);
  font-style:italic;margin-bottom:16px;
}

/* Readout Cards */
.readout-row{
  display:flex;gap:12px;flex-wrap:wrap;margin-bottom:16px;
}
.readout{
  background:var(--bg-elevated);border:1px solid var(--rule);
  border-radius:6px;padding:10px 16px;
  font-family:var(--font-mono);font-size:13px;
}
.readout .readout-label{
  font-family:var(--font-sans);font-size:10px;
  color:var(--ink-muted);text-transform:uppercase;letter-spacing:.05em;
}
.readout .readout-value{
  font-size:20px;font-weight:600;color:var(--upstream);
}

/* Callout */
.callout{
  background:rgba(200,57,44,0.06);
  border-left:3px solid var(--accent);
  padding:16px 20px;
  border-radius:0 6px 6px 0;
  margin:28px 0;
  font-size:15px;
}
.callout strong{color:var(--accent)}
.callout em{font-style:italic}

/* Chapter Foot Link */
.chapter-foot{
  display:inline-flex;align-items:center;gap:6px;
  font-family:var(--font-sans);font-size:14px;font-weight:500;
  color:var(--upstream);text-decoration:none;
  margin-top:16px;
  transition:all .2s;
}
.chapter-foot:hover{color:var(--accent)}
.chapter-foot:hover .arrow{transform:translateX(4px)}
.arrow{transition:transform .2s}

/* SVG Diagram */
.arch-diagram{
  width:100%;max-width:800px;margin:0 auto 24px;
}
.arch-diagram svg{width:100%;height:auto}

/* Strategy Cards */
.strategy-cards{
  display:flex;gap:12px;flex-wrap:wrap;margin-bottom:16px;
}
.strategy-card{
  flex:1;min-width:140px;
  background:var(--bg-elevated);border:2px solid var(--rule);
  border-radius:8px;padding:14px;cursor:pointer;
  transition:all .2s;text-align:center;
}
.strategy-card.active{border-color:var(--accent);background:rgba(200,57,44,0.04)}
.strategy-card:hover{border-color:var(--midmarket)}
.strategy-card .sc-title{
  font-family:var(--font-sans);font-size:13px;font-weight:600;
  color:var(--ink);margin-bottom:4px;
}
.strategy-card .sc-desc{
  font-size:12px;color:var(--ink-muted);line-height:1.4;
}

/* Button */
.btn{
  font-family:var(--font-sans);font-size:13px;font-weight:600;
  padding:8px 20px;border:2px solid var(--accent);
  border-radius:6px;background:transparent;color:var(--accent);
  cursor:pointer;transition:all .2s;
}
.btn:hover{background:var(--accent);color:white}
.btn.active{background:var(--accent);color:white}

/* Footer */
.site-footer{
  max-width:var(--max-w);margin:0 auto;
  padding:3rem 24px 4rem;
  text-align:center;
  font-family:var(--font-sans);font-size:13px;
  color:var(--ink-muted);
  border-top:1px solid var(--rule);
}
.site-footer a{color:var(--accent);text-decoration:none}
.site-footer a:hover{text-decoration:underline}

/* Utility */
.mt-0{margin-top:0}
.mb-0{margin-bottom:0}
.text-center{text-align:center}
.text-sm{font-size:14px}
.text-muted{color:var(--ink-muted)}
.mono{font-family:var(--font-mono)}
.sans{font-family:var(--font-sans)}