/* ==========================================================================
   r1_Fuel — research site styles
   Built on the BlankFrame design system (warm paper / dark ink / oxford blue accent)
   ========================================================================== */

:root{
  --bg: #F2F1ED;
  --card: #FFFFFF;
  --ink: #131313;
  --ink-soft: #2A2A28;
  --muted: #6F6E6A;
  --faint: #A5A39D;
  --line: #E6E4DE;
  --accent: #1B365D;
  --accent-soft: #EDF1F7;
  --warn: #9E3A20;
  --ok: #2F6F4F;
  --radius-lg: 28px;
  --radius-md: 20px;
  --radius-sm: 12px;
  --max-w: 1140px;
  --read-w: 760px;
  --shadow-card: 0 1px 2px rgba(19,19,19,0.04), 0 10px 30px -12px rgba(19,19,19,0.10);
  --shadow-pill: 0 1px 2px rgba(19,19,19,0.06), 0 12px 32px -14px rgba(19,19,19,0.18);
}

*{ box-sizing: border-box; }
html{ scroll-behavior: smooth; }

body{
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
  -webkit-font-smoothing: antialiased;
  line-height: 1.65;
  overflow-x: hidden;
}

h1, h2, h3, h4, .display{
  font-family: 'Inter Tight', 'Inter', sans-serif;
  letter-spacing: -0.035em;
  margin: 0;
  font-weight: 700;
  line-height: 1.12;
}

.serif{
  font-family: 'Instrument Serif', Georgia, serif;
  font-style: italic;
  font-weight: 400;
  letter-spacing: -0.01em;
}

a{ color: inherit; }

.wrap{ max-width: var(--max-w); margin: 0 auto; padding: 0 24px; }
.read{ max-width: var(--read-w); margin: 0 auto; padding: 0 24px; }
@media (max-width: 640px){
  .wrap, .read{ padding: 0 16px; }
}

@media (prefers-reduced-motion: reduce){
  *{ animation: none !important; transition: none !important; }
}

/* -------------------- Nav -------------------- */
.nav-shell{
  position: sticky; top: 0; z-index: 100;
  background: rgba(242,241,237,0.82);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  border-bottom: 1px solid var(--line);
}
.nav-inner{
  max-width: var(--max-w); margin: 0 auto; padding: 12px 24px;
  display: flex; align-items: center; gap: 20px; justify-content: space-between;
}
.nav-brand{
  display: flex; align-items: baseline; gap: 10px;
  text-decoration: none; font-weight: 700; letter-spacing: -0.03em;
  font-family: 'Inter Tight', sans-serif; white-space: nowrap;
}
.nav-brand .mark{
  display: inline-block; width: 12px; height: 12px;
  border: 2.5px solid var(--ink); border-radius: 2px;
  transform: translateY(0px);
}
.nav-brand .sub{ color: var(--muted); font-weight: 500; font-size: 13px; }
.nav-links{
  display: flex; gap: 4px; align-items: center;
  overflow-x: auto; scrollbar-width: none; -ms-overflow-style: none;
}
.nav-links::-webkit-scrollbar{ display: none; }
.nav-links a{
  text-decoration: none; font-size: 13.5px; font-weight: 500; color: var(--muted);
  padding: 7px 11px; border-radius: 999px; white-space: nowrap;
  transition: background 180ms ease, color 180ms ease;
}
.nav-links a:hover{ color: var(--ink); background: rgba(19,19,19,0.05); }
.nav-links a.active{ color: var(--ink); background: var(--card); box-shadow: var(--shadow-card); }
@media (max-width: 860px){
  .nav-inner{ flex-direction: column; align-items: stretch; gap: 10px; padding: 12px 16px; }
  .nav-links{ width: 100%; }
}

/* -------------------- Hero -------------------- */
.hero{ padding: 72px 0 40px; }
.eyebrow{
  display: inline-flex; align-items: center; gap: 8px;
  font-size: 12px; font-weight: 600; letter-spacing: 0.1em; text-transform: uppercase;
  color: var(--accent); margin-bottom: 20px;
}
.eyebrow .dot{
  width: 7px; height: 7px; border-radius: 50%; background: var(--accent);
}
h1.display{ font-size: clamp(38px, 6.2vw, 68px); }
.lede{
  font-size: clamp(17px, 2.1vw, 21px); color: var(--ink-soft);
  max-width: 720px; margin-top: 24px;
}
.lede-sm{ font-size: 17px; color: var(--muted); max-width: 700px; margin-top: 16px; }

/* -------------------- Buttons -------------------- */
.btn-row{ display: flex; flex-wrap: wrap; gap: 12px; margin-top: 32px; }
.btn{
  display: inline-flex; align-items: center; gap: 8px;
  padding: 13px 22px; border-radius: 999px; text-decoration: none;
  font-weight: 600; font-size: 14.5px; border: 1px solid transparent;
  transition: transform 180ms ease, box-shadow 180ms ease, background 180ms ease;
}
.btn:hover{ transform: translateY(-1px); }
.btn-primary{ background: var(--accent); color: #fff; box-shadow: 0 10px 26px -14px rgba(255,74,31,0.9); }
.btn-primary:hover{ background: #E83F16; }
.btn-ghost{ background: var(--card); color: var(--ink); border-color: var(--line); box-shadow: var(--shadow-card); }
.btn-ghost:hover{ border-color: rgba(19,19,19,0.2); }
.btn-plain{ background: transparent; color: var(--muted); padding: 13px 8px; }
.btn-plain:hover{ color: var(--ink); }

/* -------------------- Sections -------------------- */
section{ padding: 56px 0; }
.sec-head{ margin-bottom: 36px; }
.sec-kicker{
  font-size: 12px; font-weight: 600; letter-spacing: 0.1em; text-transform: uppercase;
  color: var(--faint); margin-bottom: 12px;
}
.sec-head h2{ font-size: clamp(27px, 3.6vw, 38px); }
.sec-head p{ color: var(--muted); margin-top: 14px; max-width: 680px; font-size: 16px; }
.rule{ height: 1px; background: var(--line); border: 0; margin: 0; }

/* -------------------- Cards & grids -------------------- */
.card{
  background: var(--card); border: 1px solid var(--line); border-radius: var(--radius-md);
  padding: 26px; box-shadow: var(--shadow-card);
}
.grid{ display: grid; gap: 18px; }
.g2{ grid-template-columns: repeat(2, 1fr); }
.g3{ grid-template-columns: repeat(3, 1fr); }
.g4{ grid-template-columns: repeat(4, 1fr); }
@media (max-width: 900px){ .g3, .g4{ grid-template-columns: repeat(2, 1fr); } }
@media (max-width: 640px){ .g2, .g3, .g4{ grid-template-columns: 1fr; } }

/* -------------------- Stat tiles -------------------- */
.stat{
  background: var(--card); border: 1px solid var(--line); border-radius: var(--radius-md);
  padding: 22px; box-shadow: var(--shadow-card);
}
.stat .val{
  font-family: 'Inter Tight', sans-serif; font-weight: 700;
  font-size: clamp(30px, 4vw, 42px); letter-spacing: -0.04em; line-height: 1;
}
.stat .val.accent{ color: var(--accent); }
.stat .lbl{ margin-top: 12px; font-size: 14px; font-weight: 600; }
.stat .note{ margin-top: 6px; font-size: 13px; color: var(--muted); line-height: 1.5; }

/* -------------------- Tags -------------------- */
.tag{
  display: inline-block; font-size: 11px; font-weight: 600; letter-spacing: 0.06em;
  text-transform: uppercase; padding: 4px 10px; border-radius: 999px;
  background: rgba(19,19,19,0.05); color: var(--muted);
}
.tag.accent{ background: var(--accent-soft); color: var(--accent); }
.tag.warn{ background: #FDF0E5; color: var(--warn); }
.tag.ok{ background: #EAF3EE; color: var(--ok); }

/* -------------------- Estimate marker -------------------- */
.est{
  font-size: 11px; font-weight: 600; color: var(--muted);
  background: rgba(19,19,19,0.05); border-radius: 4px; padding: 1px 5px;
  vertical-align: 2px; letter-spacing: 0.02em;
}

/* -------------------- Tables -------------------- */
.table-wrap{ overflow-x: auto; -webkit-overflow-scrolling: touch; }
table.data{
  width: 100%; border-collapse: collapse; font-size: 14.5px;
  font-variant-numeric: tabular-nums; min-width: 460px;
}
table.data th, table.data td{
  text-align: left; padding: 11px 14px; border-bottom: 1px solid var(--line);
}
table.data thead th{
  font-size: 11.5px; font-weight: 600; letter-spacing: 0.07em; text-transform: uppercase;
  color: var(--faint); border-bottom: 1px solid var(--ink);
}
table.data tbody tr:last-child td{ border-bottom: 0; }
table.data td.num, table.data th.num{ text-align: right; }
table.data tbody tr:hover{ background: rgba(19,19,19,0.018); }
table.data .hi{ font-weight: 700; color: var(--accent); }

/* -------------------- Callouts -------------------- */
.callout{
  border-left: 3px solid var(--accent); background: var(--card);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  padding: 18px 22px; margin: 26px 0; box-shadow: var(--shadow-card);
}
.callout .k{
  font-size: 11px; font-weight: 700; letter-spacing: 0.1em; text-transform: uppercase;
  color: var(--accent); display: block; margin-bottom: 8px;
}
.callout.neutral{ border-left-color: var(--faint); }
.callout.neutral .k{ color: var(--muted); }

/* -------------------- Loop diagram -------------------- */
.loop-fig{
  background: var(--card); border: 1px solid var(--line); border-radius: var(--radius-md);
  padding: 26px; box-shadow: var(--shadow-card); overflow-x: auto;
}
.loop-fig svg{ display: block; margin: 0 auto; max-width: 100%; height: auto; }
.fig-cap{ font-size: 13.5px; color: var(--muted); margin-top: 16px; line-height: 1.55; }

/* -------------------- Timeline -------------------- */
.tl{ position: relative; padding-left: 26px; }
.tl::before{
  content: ''; position: absolute; left: 5px; top: 8px; bottom: 8px;
  width: 2px; background: var(--line);
}
.tl-item{ position: relative; padding-bottom: 26px; }
.tl-item:last-child{ padding-bottom: 0; }
.tl-item::before{
  content: ''; position: absolute; left: -26px; top: 7px;
  width: 12px; height: 12px; border-radius: 50%;
  background: var(--bg); border: 2.5px solid var(--faint);
}
.tl-item.hot::before{ border-color: var(--accent); background: var(--accent); }
.tl-item.done::before{ border-color: var(--ok); background: var(--ok); }
.tl-when{ font-size: 12px; font-weight: 600; letter-spacing: 0.06em; text-transform: uppercase; color: var(--accent); }
.tl-item:not(.hot) .tl-when{ color: var(--faint); }
.tl-what{ font-weight: 600; margin-top: 4px; font-family: 'Inter Tight', sans-serif; font-size: 17px; }
.tl-why{ color: var(--muted); font-size: 14.5px; margin-top: 4px; }

/* -------------------- Checklist -------------------- */
ul.check{ list-style: none; padding: 0; margin: 0; }
ul.check li{
  position: relative; padding-left: 28px; margin-bottom: 11px;
  color: var(--ink-soft); font-size: 15px;
}
ul.check li::before{
  content: ''; position: absolute; left: 0; top: 7px;
  width: 8px; height: 8px; border-radius: 2px; background: var(--accent);
}
ul.check li.off{ color: var(--muted); }
ul.check li.off::before{ background: transparent; border: 1.5px solid var(--faint); }

/* -------------------- Prose (markdown pages) -------------------- */
.prose{ font-size: 16.5px; color: var(--ink-soft); }
.prose > *:first-child{ margin-top: 0; }
.prose h1{ font-size: clamp(30px, 4.4vw, 44px); margin: 0 0 24px; color: var(--ink); }
.prose h2{
  font-size: clamp(23px, 3vw, 30px); margin: 56px 0 18px; color: var(--ink);
  padding-top: 22px; border-top: 1px solid var(--line);
}
.prose h3{ font-size: 20px; margin: 36px 0 14px; color: var(--ink); }
.prose h4{ font-size: 16.5px; margin: 28px 0 10px; color: var(--ink); }
.prose p{ margin: 0 0 18px; }
.prose ul, .prose ol{ margin: 0 0 18px; padding-left: 22px; }
.prose li{ margin-bottom: 8px; }
.prose li > ul, .prose li > ol{ margin-top: 8px; }
.prose strong{ color: var(--ink); font-weight: 600; }
.prose a{ color: var(--accent); text-decoration: none; border-bottom: 1px solid rgba(255,74,31,0.28); }
.prose a:hover{ border-bottom-color: var(--accent); }
.prose blockquote{
  margin: 24px 0; padding: 4px 0 4px 20px;
  border-left: 3px solid var(--line); color: var(--muted);
}
.prose code{
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace; font-size: 0.875em;
  background: rgba(19,19,19,0.05); padding: 2px 6px; border-radius: 5px; color: var(--ink);
}
.prose pre{
  background: #16161A; color: #E8E6E1; padding: 20px; border-radius: var(--radius-sm);
  overflow-x: auto; font-size: 13px; line-height: 1.55; margin: 24px 0;
}
.prose pre code{ background: none; padding: 0; color: inherit; font-size: inherit; }
.prose hr{ border: 0; border-top: 1px solid var(--line); margin: 40px 0; }
.prose img{ max-width: 100%; height: auto; border-radius: var(--radius-sm); }
.prose table{
  width: 100%; border-collapse: collapse; font-size: 14.5px; margin: 26px 0;
  font-variant-numeric: tabular-nums;
}
.prose table th, .prose table td{
  text-align: left; padding: 10px 13px; border-bottom: 1px solid var(--line);
  vertical-align: top;
}
.prose table thead th{
  font-size: 11.5px; font-weight: 600; letter-spacing: 0.07em; text-transform: uppercase;
  color: var(--faint); border-bottom: 1px solid var(--ink); white-space: nowrap;
}
.prose .tbl{ overflow-x: auto; -webkit-overflow-scrolling: touch; margin: 26px 0; }
.prose .tbl table{ margin: 0; min-width: 520px; }

/* -------------------- Doc header + TOC -------------------- */
.doc-head{ padding: 56px 0 30px; border-bottom: 1px solid var(--line); margin-bottom: 40px; }
.doc-head .kicker{
  font-size: 12px; font-weight: 600; letter-spacing: 0.1em; text-transform: uppercase;
  color: var(--accent); margin-bottom: 14px;
}
.doc-head h1{ font-size: clamp(32px, 5vw, 50px); }
.doc-head .meta{ color: var(--muted); font-size: 15px; margin-top: 18px; }
.toc{
  background: var(--card); border: 1px solid var(--line); border-radius: var(--radius-md);
  padding: 22px 26px; margin-bottom: 44px; box-shadow: var(--shadow-card);
}
.toc .t{
  font-size: 11.5px; font-weight: 600; letter-spacing: 0.1em; text-transform: uppercase;
  color: var(--faint); margin-bottom: 12px;
}
.toc ol{ margin: 0; padding-left: 18px; font-size: 15px; }
.toc li{ margin-bottom: 7px; }
.toc a{ color: var(--ink-soft); text-decoration: none; }
.toc a:hover{ color: var(--accent); }

/* -------------------- Footer -------------------- */
footer{
  border-top: 1px solid var(--line); margin-top: 72px; padding: 44px 0 56px;
  color: var(--muted); font-size: 14px;
}
footer .fgrid{ display: flex; flex-wrap: wrap; gap: 32px; justify-content: space-between; }
footer a{ color: var(--muted); text-decoration: none; }
footer a:hover{ color: var(--accent); }
footer .flinks{ display: flex; flex-wrap: wrap; gap: 18px; }
footer .fnote{ margin-top: 26px; font-size: 13px; color: var(--faint); max-width: 620px; line-height: 1.6; }

/* -------------------- Misc -------------------- */
.mono{ font-family: ui-monospace, SFMono-Regular, Menlo, monospace; font-size: 0.9em; }
.muted{ color: var(--muted); }
.small{ font-size: 13.5px; }
.mt0{ margin-top: 0; } .mb0{ margin-bottom: 0; }
.center{ text-align: center; }
.copy-field{
  display: flex; align-items: center; gap: 10px; flex-wrap: wrap;
  background: rgba(19,19,19,0.04); border-radius: var(--radius-sm);
  padding: 12px 16px; font-family: ui-monospace, Menlo, monospace; font-size: 14px;
}