/* === Session 2: Production Agents === */
:root {
  --bg: #fbfbfa;
  --bg-elev: #ffffff;
  --bg-sunken: #f4f4f1;
  --ink: #1a1a1a;
  --ink-2: #3d3d3a;
  --ink-3: #6b6b66;
  --ink-4: #a3a39d;
  --line: #e7e7e2;
  --line-strong: #d4d4cc;
  --accent: #2d5fb8;       /* deep blue */
  --accent-soft: #e8f0fe;
  --accent-ink: #1d3f7d;
  --warm: #c7521c;         /* terracotta */
  --warm-soft: #fbeadc;
  --green: #2e7d4f;
  --green-soft: #e3f1e8;
  --violet: #6b3fa0;
  --violet-soft: #ede4f7;
  --amber: #b8861a;
  --amber-soft: #fbf0d2;
  --rose: #b3315a;
  --rose-soft: #fde4eb;

  --serif: "Source Serif 4", "Source Serif Pro", ui-serif, Georgia, serif;
  --sans: "Inter Tight", "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", system-ui, sans-serif;
  --mono: "JetBrains Mono", ui-monospace, "SF Mono", "Menlo", monospace;

  --radius: 6px;
  --radius-lg: 12px;
  --shadow-sm: 0 1px 2px rgba(20, 20, 20, 0.04);
  --shadow: 0 4px 16px -4px rgba(20, 20, 20, 0.08), 0 2px 4px rgba(20, 20, 20, 0.04);
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  background: var(--bg);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 17px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

/* === Layout === */
.shell { max-width: 1200px; margin: 0 auto; padding: 0 32px; }
.col { max-width: 720px; margin: 0 auto; }
.col-wide { max-width: 920px; margin: 0 auto; }

/* === Sticky chrome === */
.topbar {
  position: sticky; top: 0; z-index: 50;
  background: rgba(251, 251, 250, 0.85);
  backdrop-filter: saturate(140%) blur(12px);
  -webkit-backdrop-filter: saturate(140%) blur(12px);
  border-bottom: 1px solid var(--line);
}
.topbar-inner {
  display: flex; align-items: center; gap: 24px;
  padding: 14px 32px;
  max-width: 1200px; margin: 0 auto;
}
.brand {
  font-family: var(--serif);
  font-weight: 600;
  font-size: 17px;
  letter-spacing: -0.01em;
}
.brand .dot {
  display: inline-block; width: 8px; height: 8px;
  background: var(--warm); border-radius: 2px; margin-right: 10px;
  transform: translateY(-1px);
}
.crumbs {
  display: flex; gap: 4px; align-items: center;
  font-size: 13px; color: var(--ink-3);
  font-variant-numeric: tabular-nums;
}
.crumbs span.sep { color: var(--ink-4); }
.crumbs .now { color: var(--ink); font-weight: 500; }
.topbar-right {
  margin-left: auto;
  display: flex; gap: 16px; align-items: center;
  font-size: 13px; color: var(--ink-3);
  font-variant-numeric: tabular-nums;
}

.progress-rail {
  position: absolute; bottom: -1px; left: 0; right: 0; height: 2px;
  background: transparent;
}
.progress-fill {
  height: 100%; background: var(--ink); width: 0%;
  transition: width 0.1s linear;
}

/* === Hero === */
.hero {
  padding: 96px 0 80px;
  border-bottom: 1px solid var(--line);
}
.eyebrow {
  font-size: 12px; letter-spacing: 0.14em; text-transform: uppercase;
  color: var(--ink-3); font-weight: 600;
  display: flex; align-items: center; gap: 12px;
}
.eyebrow .pip { width: 6px; height: 6px; background: var(--warm); border-radius: 50%; }
.hero h1 {
  font-family: var(--serif);
  font-weight: 500;
  font-size: 64px;
  line-height: 1.04;
  letter-spacing: -0.025em;
  margin: 24px 0 24px;
  color: var(--ink);
}
.hero h1 em {
  font-style: italic;
  color: var(--warm);
}
.hero-sub {
  font-size: 21px; line-height: 1.5;
  color: var(--ink-2);
  max-width: 620px;
  margin: 0 0 40px;
}
.hero-meta {
  display: flex; gap: 32px;
  padding-top: 28px;
  border-top: 1px solid var(--line);
  font-size: 13px;
  color: var(--ink-3);
}
.hero-meta div { display: flex; flex-direction: column; gap: 2px; }
.hero-meta strong { color: var(--ink); font-weight: 500; font-size: 15px; }

/* === Chapter intro === */
.chapter-intro {
  padding: 96px 0 48px;
  border-top: 1px solid var(--line);
  background:
    linear-gradient(to bottom, var(--bg-sunken) 0%, var(--bg) 100%);
}
.chapter-intro .num {
  font-family: var(--serif);
  font-size: 92px;
  font-weight: 300;
  font-style: italic;
  color: var(--warm);
  line-height: 0.9;
  letter-spacing: -0.04em;
}
.chapter-intro h2 {
  font-family: var(--serif);
  font-weight: 500;
  font-size: 44px;
  letter-spacing: -0.02em;
  margin: 8px 0 20px;
  line-height: 1.1;
}
.chapter-intro p {
  font-size: 19px; color: var(--ink-2);
  max-width: 580px;
  margin: 0;
}
.chapter-toc {
  margin-top: 56px;
  display: grid; grid-template-columns: repeat(3, 1fr);
  gap: 1px; background: var(--line);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  overflow: hidden;
}
.chapter-toc .item {
  background: var(--bg-elev); padding: 20px 24px;
  display: flex; flex-direction: column; gap: 4px;
}
.chapter-toc .item .idx {
  font-family: var(--mono); font-size: 11px; color: var(--ink-3);
  letter-spacing: 0.04em;
}
.chapter-toc .item .title { font-weight: 500; font-size: 15px; }
.chapter-toc .item .min { font-size: 12px; color: var(--ink-3); margin-top: 2px; }

/* === Topic === */
.topic {
  padding: 96px 0 80px;
  border-top: 1px solid var(--line);
}
.topic-head {
  display: flex; align-items: baseline; gap: 16px;
  margin-bottom: 12px;
}
.topic-head .tag {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.06em;
  color: var(--ink-3);
  background: var(--bg-sunken);
  padding: 4px 8px;
  border-radius: 3px;
  border: 1px solid var(--line);
  text-transform: uppercase;
}
.topic-head .est {
  font-size: 12px; color: var(--ink-3);
  margin-left: auto;
  font-variant-numeric: tabular-nums;
}
.topic h3 {
  font-family: var(--serif);
  font-weight: 500;
  font-size: 36px;
  letter-spacing: -0.02em;
  line-height: 1.15;
  margin: 0 0 16px;
}
.topic .lede {
  font-size: 20px; color: var(--ink-2); line-height: 1.5;
  margin: 0 0 40px;
  max-width: 640px;
}
.topic h4 {
  font-family: var(--sans);
  font-weight: 600;
  font-size: 14px;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--ink-3);
  margin: 48px 0 16px;
}
.topic p {
  margin: 0 0 16px;
  color: var(--ink-2);
}
.topic strong { color: var(--ink); font-weight: 600; }
.topic ul { margin: 0 0 16px; padding-left: 20px; color: var(--ink-2); }
.topic ul li { margin-bottom: 6px; }
.topic ul li::marker { color: var(--ink-4); }

/* === Frame: animation panel === */
.frame {
  background: var(--bg-elev);
  border: 1px solid var(--line);
  border-radius: var(--radius-lg);
  margin: 32px 0;
  overflow: hidden;
  box-shadow: var(--shadow-sm);
}
.frame-head {
  display: flex; align-items: center; gap: 12px;
  padding: 12px 16px;
  border-bottom: 1px solid var(--line);
  background: var(--bg-sunken);
  font-family: var(--mono);
  font-size: 12px;
  color: var(--ink-3);
}
.frame-head .dots {
  display: flex; gap: 5px;
}
.frame-head .dots span {
  width: 9px; height: 9px; border-radius: 50%; background: var(--line-strong);
}
.frame-head .label { color: var(--ink-2); letter-spacing: 0.02em; }
.frame-body {
  padding: 24px;
  position: relative;
  background: var(--bg-elev);
}
.frame-controls {
  display: flex; gap: 8px; align-items: center;
  padding: 12px 16px;
  border-top: 1px solid var(--line);
  background: var(--bg-sunken);
}
.btn {
  font-family: var(--sans);
  font-size: 13px;
  font-weight: 500;
  padding: 6px 12px;
  border: 1px solid var(--line-strong);
  background: var(--bg-elev);
  color: var(--ink-2);
  border-radius: 5px;
  cursor: pointer;
  display: inline-flex; align-items: center; gap: 6px;
  transition: all 0.15s ease;
}
.btn:hover { border-color: var(--ink-3); color: var(--ink); }
.btn.primary { background: var(--ink); color: var(--bg-elev); border-color: var(--ink); }
.btn.primary:hover { background: var(--ink-2); }
.btn .ic { font-size: 11px; }
.step-readout {
  margin-left: auto;
  font-family: var(--mono);
  font-size: 12px;
  color: var(--ink-3);
}

/* === Code === */
.code {
  background: #1a1d23;
  border-radius: var(--radius);
  padding: 18px 20px;
  overflow-x: auto;
  font-family: var(--mono);
  font-size: 13px;
  line-height: 1.6;
  color: #d4d4d4;
  margin: 16px 0;
}
.code .k { color: #c586c0; }   /* keyword */
.code .s { color: #ce9178; }   /* string */
.code .c { color: #6a9955; font-style: italic; }  /* comment */
.code .f { color: #dcdcaa; }   /* function */
.code .n { color: #9cdcfe; }   /* name */
.code .t { color: #4ec9b0; }   /* type */
.code .num { color: #b5cea8; }
.code .o { color: #d4d4d4; }
.code .hl { background: rgba(255, 217, 102, 0.12); display: block; margin: 0 -20px; padding: 0 20px; }

.callout {
  border-left: 3px solid var(--accent);
  background: var(--accent-soft);
  padding: 14px 18px;
  border-radius: 0 var(--radius) var(--radius) 0;
  margin: 24px 0;
  font-size: 15px;
  color: var(--accent-ink);
}
.callout.warn { border-left-color: var(--warm); background: var(--warm-soft); color: var(--warm); }
.callout strong { color: inherit; font-weight: 600; }

/* === Inline notes === */
.aside {
  font-size: 14px;
  color: var(--ink-3);
  border-left: 2px solid var(--line-strong);
  padding-left: 16px;
  margin: 20px 0;
  font-style: italic;
}

/* === Build challenge === */
.challenge {
  background: var(--bg-sunken);
  border: 1px solid var(--line);
  border-radius: var(--radius-lg);
  padding: 28px 32px;
  margin: 48px 0;
}
.challenge .label {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--warm);
  font-weight: 600;
  margin-bottom: 8px;
}
.challenge h5 {
  font-family: var(--serif);
  font-weight: 500;
  font-size: 22px;
  margin: 0 0 12px;
  letter-spacing: -0.01em;
}
.challenge p { font-size: 15px; }
.challenge ol {
  font-size: 14px; color: var(--ink-2);
  margin: 12px 0 0; padding-left: 20px;
}
.challenge ol li { margin-bottom: 6px; }

/* === Footer === */
.outro {
  padding: 120px 0 80px;
  border-top: 1px solid var(--line);
  background: var(--bg-sunken);
}
.outro h2 {
  font-family: var(--serif); font-weight: 500;
  font-size: 36px; letter-spacing: -0.02em;
  margin: 0 0 16px;
}
.outro p { font-size: 17px; color: var(--ink-2); max-width: 540px; }
.outro .signoff {
  margin-top: 64px;
  font-family: var(--mono); font-size: 12px; color: var(--ink-4);
}

/* === Anchor offset === */
[id]::before {
  content: "";
  display: block;
  height: 80px;
  margin-top: -80px;
  visibility: hidden;
  pointer-events: none;
}

/* === Tabular numerals utility === */
.mono { font-family: var(--mono); font-variant-numeric: tabular-nums; }
.tnum { font-variant-numeric: tabular-nums; }

/* === Scroll indicator === */
.scroll-hint {
  display: inline-flex; align-items: center; gap: 8px;
  font-size: 13px; color: var(--ink-3);
  margin-top: 24px;
}
.scroll-hint .arrow {
  display: inline-block;
  width: 14px; height: 14px;
  border-right: 1.5px solid var(--ink-3);
  border-bottom: 1.5px solid var(--ink-3);
  transform: rotate(45deg) translate(-2px, -2px);
  animation: nudge 1.6s ease-in-out infinite;
}
@keyframes nudge {
  0%, 100% { transform: rotate(45deg) translate(-2px, -2px); opacity: 0.6; }
  50% { transform: rotate(45deg) translate(0, 0); opacity: 1; }
}