/* ============================================================
   Agentic AI — The Complete Course
   Shared design system  ·  Apple-light theme
   ============================================================ */

*,*::before,*::after{box-sizing:border-box}
html{-webkit-text-size-adjust:100%;scroll-behavior:smooth}
body{margin:0}

:root{
  /* surfaces */
  --white:#ffffff;
  --grey:#f5f5f7;
  --grey-2:#ebebed;
  --ink:#1d1d1f;
  --sub:#6e6e73;
  --hair:#d2d2d7;
  --hair-soft:#e6e6e9;
  /* accents */
  --blue:#0071e3;
  --blue-2:#2997ff;
  --teal:#0a9d94;
  --purple:#8a4dff;
  --amber:#ff9f0a;
  --pink:#ff375f;
  --green:#26b258;
  /* tints */
  --blue-t:#eaf3fe;
  --teal-t:#e3f5f2;
  --purple-t:#f1eafe;
  --amber-t:#fff4e2;
  --pink-t:#ffe9ee;
  --green-t:#e6f7ec;
  /* geometry */
  --maxw:940px;
  --radius:22px;
  --radius-s:14px;
  --shadow:0 1px 2px rgba(0,0,0,.04),0 8px 30px rgba(0,0,0,.06);
  --shadow-lg:0 2px 6px rgba(0,0,0,.05),0 24px 70px rgba(0,0,0,.12);
  --font:-apple-system,BlinkMacSystemFont,"SF Pro Display","SF Pro Text","Segoe UI",Roboto,Helvetica,Arial,sans-serif;
  --mono:"SF Mono",ui-monospace,"JetBrains Mono",Menlo,Consolas,monospace;
}

body{
  font-family:var(--font);
  color:var(--ink);
  background:var(--white);
  line-height:1.5;
  -webkit-font-smoothing:antialiased;
  text-rendering:optimizeLegibility;
}

/* ---------- progress + top bar ---------- */
.pbar{position:fixed;top:0;left:0;height:3px;width:0%;
  background:linear-gradient(90deg,var(--blue),var(--purple));z-index:100;transition:width .1s linear}
.tbar{position:sticky;top:0;z-index:90;display:flex;align-items:center;justify-content:space-between;
  gap:16px;padding:13px clamp(18px,5vw,40px);
  background:rgba(255,255,255,.72);backdrop-filter:saturate(180%) blur(20px);
  -webkit-backdrop-filter:saturate(180%) blur(20px);border-bottom:1px solid var(--hair-soft)}
.tbar .home{font-weight:600;font-size:15px;color:var(--ink);text-decoration:none;letter-spacing:-.01em;
  display:inline-flex;align-items:center;gap:9px}
.tbar .home .dot{width:11px;height:11px;border-radius:50%;
  background:conic-gradient(from 0deg,var(--blue),var(--purple),var(--teal),var(--blue))}
.tbar .cx{font-size:13px;color:var(--sub);font-variant-numeric:tabular-nums}
.tbar a{text-decoration:none}

/* ---------- layout ---------- */
.wrap{max-width:var(--maxw);margin:0 auto;padding:0 clamp(20px,6vw,32px)}
.band{padding:clamp(56px,9vw,104px) 0}
.band-grey{background:var(--grey)}
.band-dark{background:#0b0b0f;color:#f5f5f7}
.band-dark .sub,.band-dark .lead{color:#a1a1a6}
.narrow{max-width:720px;margin-left:auto;margin-right:auto}
.center{text-align:center}

/* ---------- type ---------- */
.eyebrow{font-size:14px;font-weight:600;letter-spacing:.02em;margin:0 0 14px;text-transform:none}
.eyebrow.blue{color:var(--blue)}.eyebrow.teal{color:var(--teal)}.eyebrow.purple{color:var(--purple)}
.eyebrow.amber{color:var(--amber)}.eyebrow.pink{color:var(--pink)}
h1,h2,h3,h4{letter-spacing:-.022em;line-height:1.06;margin:0 0 .5em;font-weight:700}
h1{font-size:clamp(38px,6.4vw,68px);font-weight:800;letter-spacing:-.03em}
h2{font-size:clamp(28px,4.4vw,44px)}
h3{font-size:clamp(21px,2.6vw,27px);letter-spacing:-.018em}
h4{font-size:18px;letter-spacing:-.01em;margin-bottom:.35em}
p{margin:0 0 1.05em}
.lead{font-size:clamp(19px,2.3vw,23px);line-height:1.5;color:#40404a;font-weight:400}
.sub{color:var(--sub)}
.prose{font-size:17.5px;line-height:1.62;color:#33333a}
.prose p{margin:0 0 1.15em}
.prose strong{font-weight:650;color:var(--ink)}
.prose em{font-style:italic}
.big{font-size:clamp(24px,3.4vw,34px);font-weight:600;letter-spacing:-.02em;line-height:1.28}
.mono{font-family:var(--mono)}
.hl{background:linear-gradient(transparent 62%,var(--amber-t) 0);padding:0 2px}
mark{background:var(--amber-t);color:var(--ink);border-radius:4px;padding:.05em .28em}
a.link{color:var(--blue);text-decoration:none;border-bottom:1px solid rgba(0,113,227,.3)}
a.link:hover{border-bottom-color:var(--blue)}

/* ---------- chapter hero ---------- */
.chero{padding:clamp(40px,7vw,64px) 0 clamp(30px,5vw,48px)}
.chero .kick{display:inline-flex;align-items:center;gap:10px;font-size:14px;font-weight:600;color:var(--sub);margin-bottom:22px}
.chero .kick .num{display:inline-grid;place-items:center;min-width:30px;height:30px;padding:0 9px;border-radius:9px;
  background:var(--ink);color:#fff;font-size:14px;font-weight:700}
.chero h1{margin-bottom:.32em}
.chero .lead{max-width:680px}
.chips{display:flex;flex-wrap:wrap;gap:9px;margin-top:26px}
.chip{font-size:13px;font-weight:550;color:#43434b;background:var(--grey);border:1px solid var(--hair-soft);
  padding:7px 13px;border-radius:999px}

/* ---------- cards / callouts ---------- */
.card{background:var(--white);border:1px solid var(--hair-soft);border-radius:var(--radius);
  padding:26px 28px;box-shadow:var(--shadow)}
.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:820px){.g2,.g3,.g4{grid-template-columns:1fr}}

.callout{background:var(--grey);border:1px solid var(--hair-soft);border-radius:var(--radius);
  padding:22px 24px;margin:26px 0}
.callout .tag{display:inline-flex;align-items:center;gap:8px;font-size:13px;font-weight:700;
  text-transform:uppercase;letter-spacing:.05em;color:var(--sub);margin-bottom:9px}
.callout.key{background:var(--blue-t);border-color:#d3e6fb}
.callout.key .tag{color:var(--blue)}
.callout.warn{background:var(--amber-t);border-color:#f6e2bf}
.callout.warn .tag{color:#b7791f}
.callout p:last-child{margin-bottom:0}

.keyidea{border-left:4px solid var(--purple);background:var(--purple-t);border-radius:0 var(--radius-s) var(--radius-s) 0;
  padding:20px 24px;margin:28px 0}
.keyidea .k{font-size:12.5px;font-weight:700;letter-spacing:.06em;text-transform:uppercase;color:var(--purple);margin-bottom:7px}
.keyidea p{margin:0;font-size:19px;font-weight:500;letter-spacing:-.01em;line-height:1.4}

/* figure + diagram shells */
figure{margin:34px 0}
figure svg{display:block;width:100%;height:auto}
figcaption{text-align:center;font-size:14px;color:var(--sub);margin-top:14px;line-height:1.45}
.stage{background:var(--white);border:1px solid var(--hair-soft);border-radius:var(--radius);
  box-shadow:var(--shadow);padding:clamp(18px,3vw,30px);margin:30px 0;position:relative;overflow:hidden}
.stage.dark{background:#0b0b0f;border-color:#26262c}
.stage .cap{font-size:13.5px;color:var(--sub);text-align:center;margin-top:16px}
.stage.dark .cap{color:#8b8b93}

/* controls */
.ctl{display:flex;flex-wrap:wrap;align-items:center;gap:12px;justify-content:center;margin-top:18px}
.btn{appearance:none;border:none;cursor:pointer;font-family:inherit;font-weight:600;font-size:15px;
  color:#fff;background:var(--blue);border-radius:999px;padding:11px 22px;transition:transform .12s,background .2s}
.btn:hover{background:#0263c6}.btn:active{transform:scale(.97)}
.btn.ghost{background:var(--grey);color:var(--ink);border:1px solid var(--hair)}
.btn.ghost:hover{background:var(--grey-2)}
.btn.sm{padding:8px 16px;font-size:13.5px}
.slider{-webkit-appearance:none;appearance:none;width:min(320px,72vw);height:5px;border-radius:5px;
  background:var(--hair);outline:none}
.slider::-webkit-slider-thumb{-webkit-appearance:none;width:22px;height:22px;border-radius:50%;
  background:var(--blue);cursor:pointer;box-shadow:0 1px 5px rgba(0,0,0,.25);border:3px solid #fff}
.slider::-moz-range-thumb{width:22px;height:22px;border-radius:50%;background:var(--blue);cursor:pointer;border:3px solid #fff}
.readout{font-family:var(--mono);font-size:14px;color:var(--ink);background:var(--grey);
  border:1px solid var(--hair-soft);border-radius:8px;padding:5px 11px;font-variant-numeric:tabular-nums}

/* legend */
.legend{display:flex;flex-wrap:wrap;gap:16px;justify-content:center;margin-top:16px;font-size:13px;color:var(--sub)}
.legend span{display:inline-flex;align-items:center;gap:7px}
.legend i{width:13px;height:13px;border-radius:4px;display:inline-block}

/* code */
.code{background:#0b0b0f;border-radius:var(--radius-s);overflow:hidden;margin:26px 0;font-family:var(--mono);font-size:14px}
.code .bar{display:flex;gap:7px;align-items:center;padding:11px 15px;background:#15151b;border-bottom:1px solid #26262c}
.code .bar i{width:11px;height:11px;border-radius:50%;background:#3a3a42}
.code .bar .nm{margin-left:8px;color:#8b8b93;font-size:12px}
.code pre{margin:0;padding:16px 18px;color:#e6e6ea;overflow-x:auto;line-height:1.6}
.code .cm{color:#7f8593}.code .kw{color:#c58fff}.code .st{color:#7fd0a0}.code .fn{color:#61b8ff}

/* ---------- reveal on scroll ---------- */
.reveal{opacity:0;transform:translateY(26px);transition:opacity .7s cubic-bezier(.2,.7,.2,1),transform .7s cubic-bezier(.2,.7,.2,1)}
.reveal.in{opacity:1;transform:none}
.reveal.d1{transition-delay:.08s}.reveal.d2{transition-delay:.16s}.reveal.d3{transition-delay:.24s}.reveal.d4{transition-delay:.32s}
@media(prefers-reduced-motion:reduce){.reveal{opacity:1;transform:none;transition:none}}

/* ---------- chapter nav ---------- */
.cnav{display:grid;grid-template-columns:1fr 1fr;gap:14px;margin:8px 0 10px}
.cnav a{display:block;padding:20px 22px;border:1px solid var(--hair-soft);border-radius:var(--radius-s);
  text-decoration:none;background:var(--white);transition:border-color .2s,transform .12s}
.cnav a:hover{border-color:var(--blue);transform:translateY(-2px)}
.cnav .dir{font-size:12.5px;color:var(--sub);font-weight:600}
.cnav .ttl{display:block;margin-top:5px;font-size:16px;font-weight:650;color:var(--ink);letter-spacing:-.01em}
.cnav a.next{text-align:right}
.cnav a.disabled{opacity:.45;pointer-events:none}
@media(max-width:640px){.cnav{grid-template-columns:1fr}.cnav a.next{text-align:left}}

/* deck link banner */
.deckcta{display:flex;align-items:center;gap:16px;flex-wrap:wrap;justify-content:space-between;
  background:var(--ink);color:#fff;border-radius:var(--radius);padding:22px 26px;margin:34px 0}
.deckcta h4{margin:0;color:#fff;font-size:18px}
.deckcta p{margin:4px 0 0;color:#b0b0b8;font-size:14px}
.deckcta a{background:#fff;color:var(--ink);font-weight:600;font-size:14.5px;padding:11px 20px;
  border-radius:999px;text-decoration:none;white-space:nowrap}

hr{border:none;border-top:1px solid var(--hair-soft);margin:44px 0}