/* ═══════════════════════════════════════════════════════════════
   THE FOUNDER'S GUIDE TO PRODUCT-MARKET FIT
   Apple-inspired editorial guide · cool neutrals + navy + amber
   System sans, weight-driven hierarchy, generous reading column.
   ═══════════════════════════════════════════════════════════════ */

:root {
  --bg:        #f5f5f7;   /* page off-white */
  --paper:    #ffffff;   /* reading surface */
  --ink:      #1d1d1f;
  --ink-2:    #424245;
  --ink-3:    #6e6e73;
  --ink-4:    #a1a1a6;
  --rule:     rgba(0,0,0,0.10);
  --rule-2:   rgba(0,0,0,0.055);
  --navy:     #1d2b4a;
  --navy-2:   #2d3e63;
  --amber:    #c8813a;
  --amber-ink:#7a4d1c;
  --bone:     #ededf0;
  --ok:       #1f7a4d;
  --bad:      #9b2c2c;

  --col:      720px;   /* reading column width */
  --wide:     1040px;  /* wide blocks */
  --gutter:   clamp(24px, 6vw, 96px);
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "SF Pro Display", "Helvetica Neue", Helvetica, Arial, sans-serif;
  font-feature-settings: "ss01", "cv11";
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  line-height: 1.6;
  font-size: 20px;
}

::selection { background: var(--amber); color: #fff; }

/* ── Top bar ─────────────────────────────────────────────────── */
.topbar {
  position: sticky;
  top: 0;
  z-index: 100;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 var(--gutter);
  height: 64px;
  background: rgba(245,245,247,0.78);
  backdrop-filter: saturate(180%) blur(20px);
  -webkit-backdrop-filter: saturate(180%) blur(20px);
  border-bottom: 1px solid var(--rule-2);
}
.topbar .wordmark {
  font-size: 15px;
  font-weight: 600;
  letter-spacing: -0.01em;
  color: var(--ink);
}
.topbar .wordmark span { color: var(--ink-3); font-weight: 500; }
.topbar nav {
  display: flex;
  gap: 22px;
  font-size: 14px;
  font-weight: 500;
}
.topbar nav a { white-space: nowrap; }
@media (max-width: 880px) {
  .topbar .wordmark span { display: none; }
  .topbar nav { gap: 16px; font-size: 13px; }
}
@media (max-width: 680px) {
  .topbar { height: auto; flex-direction: column; align-items: flex-start; gap: 6px; padding-top: 10px; padding-bottom: 10px; }
  .topbar nav { flex-wrap: wrap; gap: 12px 16px; }
}
.topbar nav a {
  color: var(--ink-3);
  text-decoration: none;
  transition: color 160ms ease;
}
.topbar nav a:hover { color: var(--ink); }
.topbar .progress {
  position: absolute;
  left: 0; bottom: -1px;
  height: 2px;
  background: var(--amber);
  width: 0;
}

/* ── Layout primitives ───────────────────────────────────────── */
.wrap   { max-width: var(--col);  margin: 0 auto; padding: 0 var(--gutter); }
.wrap-w { max-width: var(--wide); margin: 0 auto; padding: 0 var(--gutter); }

section { padding: 0; }

/* ── Hero ────────────────────────────────────────────────────── */
.hero {
  background: #000;
  color: #f5f5f7;
  padding: clamp(80px, 14vh, 180px) 0 clamp(72px, 12vh, 140px);
  position: relative;
  overflow: hidden;
}
.hero .eyebrow { color: var(--amber); }
.hero h1 {
  font-size: clamp(56px, 9vw, 128px);
  font-weight: 700;
  letter-spacing: -0.045em;
  line-height: 0.96;
  margin: 28px 0 0;
}
.hero h1 .accent { color: var(--amber); }
.hero .sub {
  margin-top: 36px;
  font-size: clamp(20px, 2.6vw, 30px);
  line-height: 1.35;
  color: rgba(245,245,247,0.74);
  font-weight: 400;
  max-width: 30ch;
  letter-spacing: -0.015em;
}
.hero .byline {
  margin-top: 56px;
  padding-top: 28px;
  border-top: 1px solid rgba(255,255,255,0.16);
  display: flex;
  flex-wrap: wrap;
  gap: 8px 28px;
  font-size: 15px;
  letter-spacing: 0.04em;
  color: rgba(245,245,247,0.6);
  font-weight: 500;
}
.hero .byline strong { color: #fff; font-weight: 600; }

/* ── Eyebrow / kickers ───────────────────────────────────────── */
.eyebrow {
  font-size: 14px;
  letter-spacing: 0.22em;
  text-transform: uppercase;
  font-weight: 600;
  color: var(--navy);
  margin: 0;
}

/* ── Typography ──────────────────────────────────────────────── */
h2, h3, h4 { margin: 0; letter-spacing: -0.025em; line-height: 1.1; font-weight: 600; }
h2 { font-size: clamp(34px, 5vw, 56px); letter-spacing: -0.03em; }
h3 { font-size: clamp(26px, 3.4vw, 38px); }
h4 { font-size: 22px; letter-spacing: -0.01em; }

p { margin: 0 0 1.2em; color: var(--ink-2); }
p:last-child { margin-bottom: 0; }
.lede { font-size: clamp(22px, 2.8vw, 28px); line-height: 1.4; color: var(--ink); font-weight: 400; letter-spacing: -0.015em; }
strong { font-weight: 600; color: var(--ink); }
em { font-style: italic; }
a { color: var(--navy); }

/* ── "How to use" intro band ─────────────────────────────────── */
.intro {
  background: var(--paper);
  padding: clamp(64px, 10vh, 120px) 0;
  border-bottom: 1px solid var(--rule);
}
.intro .grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: clamp(32px, 5vw, 72px);
  margin-top: 48px;
}
@media (max-width: 760px) { .intro .grid { grid-template-columns: 1fr; gap: 32px; } }
.intro .grid .item .n {
  font-size: 13px; letter-spacing: 0.18em; text-transform: uppercase;
  color: var(--amber-ink); font-weight: 700;
}
.intro .grid .item h4 { margin: 10px 0 8px; }
.intro .grid .item p { font-size: 18px; color: var(--ink-3); margin: 0; }

/* ── Framework / TOC ─────────────────────────────────────────── */
.toc {
  background: var(--bg);
  padding: clamp(64px, 10vh, 120px) 0;
}
.toc-list { margin-top: 56px; display: grid; gap: 0; border-top: 1px solid var(--rule); }
.toc-item {
  display: grid;
  grid-template-columns: 88px 1fr auto;
  gap: 28px;
  align-items: baseline;
  padding: 28px 8px;
  border-bottom: 1px solid var(--rule);
  text-decoration: none;
  color: var(--ink);
  transition: padding-left 200ms ease, background 200ms ease;
}
.toc-item:hover { padding-left: 20px; background: var(--paper); }
.toc-item .num {
  font-size: 28px; font-weight: 700; letter-spacing: -0.03em;
  color: var(--ink-4); font-variant-numeric: tabular-nums;
}
.toc-item:hover .num { color: var(--amber); }
.toc-item .t { font-size: clamp(22px, 2.6vw, 30px); font-weight: 600; letter-spacing: -0.02em; }
.toc-item .d { font-size: 16px; color: var(--ink-3); margin-top: 4px; font-weight: 400; }
.toc-item .arrow { color: var(--ink-4); font-size: 22px; }
.toc-item:hover .arrow { color: var(--ink); }

/* ── Chapter ─────────────────────────────────────────────────── */
.chapter { padding: clamp(72px, 12vh, 150px) 0; }
.chapter:nth-of-type(even) { background: var(--paper); }
.chapter-head { margin-bottom: 48px; }
.chapter-num {
  font-size: clamp(80px, 16vw, 200px);
  font-weight: 700;
  letter-spacing: -0.06em;
  line-height: 0.8;
  color: var(--rule);
  font-variant-numeric: tabular-nums;
  margin-bottom: 8px;
}
.chapter:nth-of-type(even) .chapter-num { color: var(--rule-2); }
.chapter-kicker { color: var(--navy); margin-bottom: 18px; }
.chapter h2 { max-width: 18ch; }
.chapter .lede { margin-top: 28px; max-width: 34ch; }

/* body blocks inside chapters */
.block { margin-top: 40px; }
.block p { font-size: 20px; }

/* numbered principles */
.principles { margin-top: 48px; display: grid; gap: 36px; }
.principle { display: grid; grid-template-columns: 56px 1fr; gap: 24px; align-items: start; }
.principle .pn {
  font-size: 22px; font-weight: 700; letter-spacing: -0.02em;
  color: var(--amber); font-variant-numeric: tabular-nums;
  border-top: 2px solid var(--amber); padding-top: 8px;
}
.principle h4 { margin-bottom: 8px; }
.principle p { font-size: 18px; color: var(--ink-2); margin: 0; }

/* ── Phenomena example callout ───────────────────────────────── */
.example {
  margin-top: 48px;
  background: var(--navy);
  color: #f5f5f7;
  border-radius: 20px;
  padding: clamp(32px, 4vw, 48px);
  position: relative;
}
.example .tag {
  display: inline-flex; align-items: center; gap: 10px;
  font-size: 12px; letter-spacing: 0.2em; text-transform: uppercase;
  font-weight: 700; color: var(--amber);
  margin-bottom: 20px;
}
.example .tag::before {
  content: ""; width: 7px; height: 7px; border-radius: 50%; background: var(--amber);
}
.example h4 { color: #fff; font-size: clamp(24px, 3vw, 32px); margin-bottom: 14px; letter-spacing: -0.02em; }
.example p { color: rgba(245,245,247,0.82); font-size: 19px; }
.example p:last-child { margin-bottom: 0; }
.example strong { color: #fff; }

/* ── Pull quote ──────────────────────────────────────────────── */
.pullquote {
  margin: clamp(48px, 8vh, 96px) auto;
  text-align: center;
}
.pullquote q {
  display: block;
  font-size: clamp(28px, 4.4vw, 52px);
  line-height: 1.16;
  font-weight: 500;
  letter-spacing: -0.03em;
  color: var(--ink);
  quotes: none;
  text-wrap: balance;
}
.pullquote q::before, .pullquote q::after { content: ""; }
.pullquote .cite {
  margin-top: 28px; font-size: 14px; letter-spacing: 0.16em;
  text-transform: uppercase; color: var(--ink-3); font-weight: 600;
}

/* ── Compare blocks (before/after, good/bad) ─────────────────── */
.compare { margin-top: 48px; display: grid; grid-template-columns: 1fr 1fr; gap: 0; border-radius: 18px; overflow: hidden; box-shadow: 0 0 0 1px var(--rule); }
@media (max-width: 680px) { .compare { grid-template-columns: 1fr; } }
.compare .side { padding: clamp(28px, 3.5vw, 40px); }
.compare .side.bad  { background: #1a1a1d; color: #f5f5f7; }
.compare .side.good { background: var(--navy); color: #f5f5f7; }
.compare .side .lbl {
  font-size: 12px; letter-spacing: 0.2em; text-transform: uppercase; font-weight: 700;
  margin-bottom: 18px; display: flex; align-items: center; gap: 10px;
}
.compare .side.bad  .lbl { color: #ff7a7a; }
.compare .side.good .lbl { color: #5dd39e; }
.compare .side h4 { color: #fff; font-size: clamp(22px, 2.6vw, 30px); margin-bottom: 20px; }
.compare ul { list-style: none; margin: 0; padding: 0; display: grid; gap: 14px; }
.compare li { font-size: 17px; line-height: 1.4; display: flex; gap: 12px; }
.compare .bad li  { color: rgba(245,245,247,0.78); }
.compare .good li { color: rgba(245,245,247,0.88); }
.compare li::before { font-weight: 700; flex-shrink: 0; }
.compare .bad li::before  { content: "✕"; color: #ff7a7a; }
.compare .good li::before { content: "✓"; color: #5dd39e; }

/* ── Color-block trio (reused motif) ─────────────────────────── */
.trio { margin-top: 48px; display: grid; grid-template-columns: repeat(3, 1fr); gap: 0; border-radius: 18px; overflow: hidden; box-shadow: 0 0 0 1px var(--rule); }
@media (max-width: 760px) { .trio { grid-template-columns: 1fr; } }
.trio .cell { padding: clamp(28px, 3vw, 36px); display: flex; flex-direction: column; min-height: 220px; }
.trio .cell .lbl { font-size: 12px; letter-spacing: 0.2em; text-transform: uppercase; font-weight: 700; }
.trio .cell h4 { margin: 14px 0 12px; font-size: clamp(22px, 2.4vw, 28px); }
.trio .cell p { font-size: 16px; line-height: 1.45; margin: auto 0 0; }
.trio .cell.navy  { background: var(--navy); color: #f5f5f7; }
.trio .cell.navy .lbl { color: rgba(245,245,247,0.55); }
.trio .cell.navy h4 { color: #fff; }
.trio .cell.navy p { color: rgba(245,245,247,0.72); }
.trio .cell.amber { background: var(--amber); color: var(--ink); }
.trio .cell.amber .lbl { color: rgba(29,29,31,0.7); }
.trio .cell.amber p { color: rgba(29,29,31,0.78); }
.trio .cell.bone  { background: var(--bone); color: var(--ink); }
.trio .cell.bone .lbl { color: rgba(29,29,31,0.55); }
.trio .cell.bone p { color: rgba(29,29,31,0.7); }

/* ── Stat row ────────────────────────────────────────────────── */
.stats { margin-top: 48px; display: grid; grid-template-columns: repeat(4, 1fr); gap: 24px; }
@media (max-width: 680px) { .stats { grid-template-columns: 1fr 1fr; gap: 32px 24px; } }
.stat .n { font-size: clamp(48px, 6vw, 72px); font-weight: 700; letter-spacing: -0.04em; line-height: 1; font-variant-numeric: tabular-nums; }
.stat .n .accent { color: var(--amber); }
.stat .l { margin-top: 10px; font-size: 15px; color: var(--ink-3); font-weight: 500; }

/* ── Steps (ordered, big) ────────────────────────────────────── */
.steps { margin-top: 48px; display: grid; gap: 0; border-top: 1px solid var(--rule); }
.step {
  display: grid; grid-template-columns: 72px 1fr; gap: 28px;
  padding: 28px 0; border-bottom: 1px solid var(--rule); align-items: baseline;
}
.step .sn { font-size: 40px; font-weight: 700; letter-spacing: -0.03em; color: var(--ink-4); font-variant-numeric: tabular-nums; }
.step:last-child .sn { color: var(--amber); }
.step h4 { margin-bottom: 8px; }
.step p { font-size: 18px; color: var(--ink-2); margin: 0; }

/* ── Takeaways ───────────────────────────────────────────────── */
.takeaways { background: #000; color: #f5f5f7; padding: clamp(72px, 12vh, 140px) 0; }
.takeaways .eyebrow { color: var(--amber); }
.takeaways h2 { color: #fff; margin-top: 18px; max-width: 20ch; }
.takeaways .grid { margin-top: 64px; display: grid; grid-template-columns: 1fr 1fr; gap: 48px 64px; }
@media (max-width: 760px) { .takeaways .grid { grid-template-columns: 1fr; gap: 40px; } }
.takeaways .t .tn { font-size: 40px; font-weight: 700; color: var(--amber); letter-spacing: -0.03em; }
.takeaways .t h4 { color: #fff; margin: 10px 0 8px; }
.takeaways .t p { color: rgba(245,245,247,0.7); font-size: 18px; margin: 0; }

/* ── Closing motivation (rat study) ──────────────────────────── */
.closing { background: var(--navy); color: #f5f5f7; padding: clamp(72px, 12vh, 140px) 0; }
.closing .eyebrow { color: var(--amber); }
.closing h2 { color: #fff; margin-top: 18px; }
.closing .twocol { margin-top: 64px; display: grid; grid-template-columns: 1fr 1fr; gap: 0; border-radius: 18px; overflow: hidden; }
@media (max-width: 680px) { .closing .twocol { grid-template-columns: 1fr; } }
.closing .twocol .c { padding: clamp(32px, 4vw, 48px); min-width: 0; }
.closing .twocol .c.dark  { background: rgba(0,0,0,0.28); }
.closing .twocol .c.amber { background: var(--amber); color: var(--ink); }
.closing .twocol .lbl { font-size: 13px; letter-spacing: 0.22em; text-transform: uppercase; font-weight: 700; }
.closing .twocol .c.dark .lbl  { color: rgba(245,245,247,0.6); }
.closing .twocol .c.amber .lbl { color: rgba(29,29,31,0.7); }
.closing .twocol .big { font-size: clamp(56px, 8vw, 104px); font-weight: 700; letter-spacing: -0.05em; line-height: 0.9; margin: 20px 0 16px; font-variant-numeric: tabular-nums; }
.closing .twocol .c.dark .big  { color: #fff; }
.closing .twocol .c.amber .big { color: var(--ink); }
.closing .twocol .big small { display: block; font-size: 0.28em; font-weight: 600; letter-spacing: 0.04em; text-transform: uppercase; margin: 12px 0 0; opacity: 0.7; }
.closing .twocol p { font-size: 17px; }
.closing .twocol .c.dark p  { color: rgba(245,245,247,0.72); }
.closing .twocol .c.amber p { color: rgba(29,29,31,0.78); }
.closing .kicker { margin-top: 48px; font-size: clamp(22px, 3vw, 32px); font-weight: 500; letter-spacing: -0.02em; color: #fff; max-width: 36ch; text-wrap: balance; }
.closing .kicker .accent { color: var(--amber); }

/* ── Author + CTA ────────────────────────────────────────────── */
.author { background: var(--paper); padding: clamp(64px, 10vh, 120px) 0; border-top: 1px solid var(--rule); }
.author .row { display: grid; grid-template-columns: auto 1fr; gap: 40px; align-items: center; }
@media (max-width: 680px) { .author .row { grid-template-columns: 1fr; gap: 28px; } }
.author .avatar {
  width: 132px; height: 132px; border-radius: 50%;
  background: linear-gradient(135deg, var(--navy), #0a1325);
  display: flex; align-items: center; justify-content: center;
  color: #fff; font-size: 44px; font-weight: 600; letter-spacing: -0.02em;
  flex-shrink: 0; overflow: hidden;
  box-shadow: 0 0 0 1px var(--rule);
}
.author .avatar img {
  width: 100%; height: 100%; object-fit: cover;
  object-position: 50% 31%; transform: scale(2.05); transform-origin: 50% 31%;
}
.author h3 { letter-spacing: -0.02em; }
.author .title { color: var(--amber-ink); font-weight: 600; font-size: 16px; margin: 6px 0 16px; letter-spacing: 0.01em; }
.author p { font-size: 18px; color: var(--ink-2); }

.cta { background: #000; color: #f5f5f7; padding: clamp(72px, 12vh, 140px) 0; text-align: center; }
.cta h2 { color: #fff; max-width: 20ch; margin: 0 auto; }
.cta p { color: rgba(245,245,247,0.7); font-size: 20px; margin: 24px auto 40px; max-width: 44ch; }
.cta .btns { display: flex; gap: 16px; justify-content: center; flex-wrap: wrap; }
.cta a.btn {
  display: inline-flex; align-items: center; gap: 10px;
  padding: 16px 32px; border-radius: 999px; font-size: 17px; font-weight: 600;
  text-decoration: none; transition: transform 160ms ease, background 160ms ease;
}
.cta a.btn.primary { background: var(--amber); color: #1d1d1f; }
.cta a.btn.primary:hover { transform: translateY(-2px); background: #d8924a; }
.cta a.btn.ghost { background: transparent; color: #f5f5f7; box-shadow: inset 0 0 0 1px rgba(255,255,255,0.3); }
.cta a.btn.ghost:hover { background: rgba(255,255,255,0.08); }
.cta .fine { margin-top: 40px; font-size: 13px; color: rgba(245,245,247,0.4); letter-spacing: 0.04em; }

/* ── Footer ──────────────────────────────────────────────────── */
.foot { background: #000; color: rgba(245,245,247,0.5); padding: 32px 0; border-top: 1px solid rgba(255,255,255,0.1); }
.foot .row { display: flex; justify-content: space-between; flex-wrap: wrap; gap: 12px; font-size: 13px; letter-spacing: 0.04em; }

/* ── Section spacing helper ──────────────────────────────────── */
.gap-sm { margin-top: 24px; }
.gap-md { margin-top: 40px; }

/* ═══════════════════════════════════════════════════════════════
   PRINT — clean multi-page PDF (the "download" version)
   ═══════════════════════════════════════════════════════════════ */
@media print {
  @page { size: A4; margin: 18mm 16mm; }
  html, body { background: #fff !important; font-size: 11pt; }
  * { -webkit-print-color-adjust: exact; print-color-adjust: exact; }
  .topbar, .cta .btns, .scroll-hint { display: none !important; }
  .hero { background: #000 !important; padding: 40pt 0; }
  .wrap, .wrap-w { max-width: none; padding: 0; }
  .chapter, .intro, .toc, .takeaways, .closing, .author, .cta {
    padding: 24pt 0; break-inside: avoid;
  }
  .chapter { break-before: page; }
  .chapter-num { font-size: 64pt; }
  .example, .compare, .trio, .pullquote, .steps, .principle { break-inside: avoid; }
  h2, h3, h4 { break-after: avoid; }
  .hero h1 { font-size: 40pt; }
  a { color: var(--ink); text-decoration: none; }
}