/* ============================================================
   System Design Guide — design system v2
   A distinctive, editorial dark theme. Class names are stable:
   chapters rely on them. Be creative WITHIN these primitives.
   ============================================================ */

@import url('https://fonts.googleapis.com/css2?family=Fraunces:opsz,wght@9..144,400;9..144,600;9..144,900&family=Inter:wght@400;500;600;700&family=JetBrains+Mono:wght@400;600&display=swap');

:root {
  /* Core surface ramp — deep indigo-black, not flat grey */
  --bg:        #0a0b14;
  --bg-2:      #12131f;
  --bg-3:      #1b1d2e;
  --bg-4:      #24273d;
  --border:    #2c2f47;
  --border-lit:#3d4163;

  --text:      #eef0fb;
  --text-dim:  #9ba0c4;
  --text-faint:#676c92;

  /* Accent system — violet primary, cyan + lime + amber supports */
  --accent:    #8b7cff;   /* violet */
  --accent-ink:#b3a8ff;
  --cyan:      #3dd7e0;
  --lime:      #8ff04a;
  --amber:     #ffb454;
  --rose:      #ff6b81;

  --glow:      0 0 0 1px rgba(139,124,255,.25), 0 8px 30px -12px rgba(139,124,255,.5);
  --radius:    14px;
  --radius-sm: 9px;
  --maxw:      820px;

  --mono: "JetBrains Mono", ui-monospace, SFMono-Regular, Menlo, monospace;
  --sans: "Inter", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  --serif:"Fraunces", Georgia, "Times New Roman", serif;
}

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

body {
  margin: 0;
  background:
    radial-gradient(1200px 600px at 80% -10%, rgba(139,124,255,.10), transparent 60%),
    radial-gradient(900px 500px at -10% 10%, rgba(61,215,224,.06), transparent 55%),
    var(--bg);
  background-attachment: fixed;
  color: var(--text);
  font-family: var(--sans);
  line-height: 1.7;
  font-size: 16.5px;
  -webkit-font-smoothing: antialiased;
}

::selection { background: rgba(139,124,255,.35); }

/* ---------- Layout shell ---------- */
.layout { display: flex; min-height: 100vh; }

.sidebar {
  width: 290px; flex-shrink: 0;
  background: linear-gradient(180deg, var(--bg-2), rgba(18,19,31,.6));
  border-right: 1px solid var(--border);
  padding: 28px 18px; position: sticky; top: 0; height: 100vh; overflow-y: auto;
  backdrop-filter: blur(6px);
}
.sidebar::-webkit-scrollbar { width: 8px; }
.sidebar::-webkit-scrollbar-thumb { background: var(--border); border-radius: 8px; }
.sidebar h1 { font-family: var(--serif); font-size: 19px; font-weight: 900; margin: 0 0 2px; letter-spacing: -.2px; }
.sidebar .tagline { color: var(--text-faint); font-size: 12px; margin-bottom: 22px; }
.sidebar .part-title {
  font-size: 10.5px; text-transform: uppercase; letter-spacing: 1.4px;
  color: var(--accent-ink); margin: 20px 0 7px; font-weight: 700; opacity: .85;
}
.sidebar a {
  display: block; color: var(--text-dim); text-decoration: none;
  padding: 6px 12px; border-radius: 8px; font-size: 14px; position: relative;
  transition: color .15s, background .15s, padding .15s;
}
.sidebar a:hover { background: var(--bg-3); color: var(--text); padding-left: 16px; }
.sidebar a.active {
  background: linear-gradient(90deg, rgba(139,124,255,.22), transparent);
  color: #fff; font-weight: 600;
}
.sidebar a.active::before {
  content: ""; position: absolute; left: 0; top: 7px; bottom: 7px; width: 3px;
  border-radius: 3px; background: var(--accent);
}

.content { flex: 1; min-width: 0; display: flex; justify-content: center; padding: 64px 40px 140px; }
.content > article { width: 100%; max-width: var(--maxw); }

/* ---------- Typography ---------- */
article h1 {
  font-family: var(--serif); font-size: 46px; font-weight: 900; line-height: 1.05;
  margin: 0 0 14px; letter-spacing: -1px;
  background: linear-gradient(120deg, #fff 20%, var(--accent-ink));
  -webkit-background-clip: text; background-clip: text; -webkit-text-fill-color: transparent;
}
article h2 {
  font-family: var(--serif); font-size: 28px; font-weight: 600; margin: 56px 0 14px;
  letter-spacing: -.4px; display: flex; align-items: baseline; gap: 12px;
}
/* numbered section badge: <h2><span class="n">1</span> Title</h2> */
article h2 .n {
  font-family: var(--mono); font-size: 13px; font-weight: 600; color: var(--accent-ink);
  border: 1px solid var(--border-lit); border-radius: 7px; padding: 2px 9px;
  background: var(--bg-2); flex-shrink: 0; transform: translateY(-3px);
}
article h3 { font-size: 19px; font-weight: 700; margin: 32px 0 8px; color: var(--accent-ink); letter-spacing: -.2px; }
article p, article li { color: var(--text); }
article a { color: var(--accent-ink); text-decoration: none; border-bottom: 1px solid rgba(179,168,255,.3); }
article a:hover { border-bottom-color: var(--accent-ink); }

.lead { font-size: 20px; line-height: 1.55; color: var(--text-dim); margin: 0 0 10px; font-weight: 400; }
.lead b { color: var(--text); font-weight: 600; }

code {
  font-family: var(--mono); font-size: .87em;
  background: var(--bg-3); padding: 2px 7px; border-radius: 5px;
  border: 1px solid var(--border); color: var(--accent-ink);
}
pre {
  background: var(--bg-2); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 18px 20px; overflow-x: auto; position: relative;
  margin: 20px 0;
}
pre::before {
  content: "•••"; position: absolute; top: 10px; left: 16px;
  letter-spacing: 4px; color: var(--text-faint); font-size: 14px; line-height: 1;
}
pre { padding-top: 34px; }
pre code { background: none; padding: 0; border: none; color: var(--text); font-size: 13.5px; line-height: 1.7; }

/* ---------- Scaffold blocks ---------- */
.block {
  border: 1px solid var(--border); border-left: 3px solid var(--accent);
  background: linear-gradient(100deg, var(--bg-2), rgba(18,19,31,.4));
  border-radius: var(--radius); padding: 18px 22px; margin: 22px 0; position: relative;
}
.block .label {
  font-size: 10.5px; text-transform: uppercase; letter-spacing: 1.2px;
  color: var(--accent); font-weight: 700; margin-bottom: 8px; display: inline-block;
}
.block.interview { border-left-color: var(--lime); }
.block.interview .label { color: var(--lime); }
.block.tradeoff  { border-left-color: var(--amber); }
.block.tradeoff .label { color: var(--amber); }
.block.gotcha    { border-left-color: var(--rose); }
.block.gotcha .label { color: var(--rose); }
.block.aha       { border-left-color: var(--cyan); }
.block.aha .label{ color: var(--cyan); }

/* Pull-quote for memorable interview lines */
.pull {
  font-family: var(--serif); font-size: 23px; font-weight: 600; line-height: 1.4;
  color: var(--text); margin: 32px 0; padding-left: 22px;
  border-left: 4px solid var(--accent); letter-spacing: -.3px;
}

/* two-column pro/con */
.cols { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
.cols .pro h4 { color: var(--lime);  margin: 0 0 6px; font-size: 15px; }
.cols .con h4 { color: var(--rose);  margin: 0 0 6px; font-size: 15px; }
@media (max-width: 640px) { .cols { grid-template-columns: 1fr; } }

/* ---------- Tables ---------- */
table { border-collapse: collapse; width: 100%; margin: 18px 0; font-size: 14px; overflow: hidden; border-radius: var(--radius-sm); }
th, td { border: 1px solid var(--border); padding: 9px 14px; text-align: left; }
th { background: var(--bg-3); color: var(--accent-ink); font-weight: 600; letter-spacing: .2px; }
tr:nth-child(even) td { background: rgba(27,29,46,.4); }
td.num { font-family: var(--mono); text-align: right; color: var(--cyan); }

/* ---------- Diagram / animation stage ---------- */
.stage {
  border: 1px solid var(--border);
  background:
    linear-gradient(0deg, rgba(139,124,255,.04), transparent),
    var(--bg-2);
  border-radius: var(--radius); padding: 24px; margin: 28px 0;
  box-shadow: 0 20px 50px -30px rgba(0,0,0,.8);
}
.stage svg { width: 100%; height: auto; display: block; }
.stage .controls { display: flex; gap: 10px; align-items: center; margin-top: 18px; }
.stage .caption {
  color: var(--text-dim); font-size: 14.5px; margin-top: 14px; min-height: 24px;
  font-family: var(--serif); font-style: italic;
}

button {
  font-family: var(--sans); font-size: 13.5px; font-weight: 600; cursor: pointer;
  background: linear-gradient(180deg, var(--accent), #6f5fe6); color: #fff; border: none;
  padding: 9px 18px; border-radius: 9px; transition: transform .1s, box-shadow .15s;
}
button:hover { transform: translateY(-1px); box-shadow: 0 8px 20px -8px var(--accent); }
button.ghost { background: var(--bg-3); color: var(--text); border: 1px solid var(--border-lit); }
button:disabled { opacity: .35; cursor: not-allowed; transform: none; box-shadow: none; }
.step-dots { display: flex; gap: 7px; margin-left: auto; }
.step-dots span { width: 8px; height: 8px; border-radius: 50%; background: var(--border-lit); transition: .2s; }
.step-dots span.on { background: var(--accent); box-shadow: 0 0 8px var(--accent); }

/* SVG helpers */
.svg-box { fill: var(--bg-3); stroke: var(--border-lit); stroke-width: 1.5; transition: .3s; }
.svg-box.hot { fill: #2a1430; stroke: var(--rose); }
.svg-box.go  { fill: #16261a; stroke: var(--lime); }
.svg-label { fill: var(--text); font: 600 13px var(--sans); }
.svg-dim   { fill: var(--text-faint); font: 12px var(--mono); }
.svg-edge  { stroke: var(--border-lit); stroke-width: 1.6; fill: none; marker-end: url(#arrow); }
.svg-edge.live { stroke: var(--accent); stroke-width: 2.4; }

/* ---------- Quiz ---------- */
.quiz { margin: 24px 0; }
.quiz .q {
  border: 1px solid var(--border); background: var(--bg-2);
  border-radius: var(--radius); padding: 20px 22px; margin: 18px 0;
}
.quiz .q .stem { font-weight: 600; margin-bottom: 14px; font-size: 16px; }
.quiz .opt {
  display: block; width: 100%; text-align: left; margin: 9px 0; font-size: 14.5px;
  background: var(--bg-3); color: var(--text); border: 1px solid var(--border);
  padding: 11px 16px; border-radius: 10px; cursor: pointer; transition: .14s; font-family: var(--sans); font-weight: 400;
}
.quiz .opt:hover { border-color: var(--accent); transform: translateX(3px); }
.quiz .opt.correct { border-color: var(--lime); background: #15271b; color: #d8ffce; }
.quiz .opt.wrong   { border-color: var(--rose); background: #2a1518; }
.quiz .opt.disabled { cursor: default; }
.quiz .opt.disabled:hover { transform: none; }
.quiz .explain {
  margin-top: 14px; padding: 14px 16px; border-radius: 10px;
  background: var(--bg-3); font-size: 14px; color: var(--text-dim);
  border-left: 3px solid var(--cyan); display: none;
}
.quiz .explain.show { display: block; animation: fade .3s ease; }
.quiz .explain b { color: var(--text); }
@keyframes fade { from { opacity: 0; transform: translateY(-4px); } to { opacity: 1; } }

/* ---------- Page nav ---------- */
.pagenav { display: flex; justify-content: space-between; margin-top: 72px; gap: 14px; }
.pagenav a {
  text-decoration: none; color: var(--text); background: var(--bg-2);
  border: 1px solid var(--border); border-radius: var(--radius); padding: 16px 20px; flex: 1;
  transition: .15s;
}
.pagenav a:hover { border-color: var(--accent); transform: translateY(-2px); box-shadow: var(--glow); }
.pagenav .dir { font-size: 11.5px; color: var(--accent-ink); text-transform: uppercase; letter-spacing: 1px; }
.pagenav .nxt { text-align: right; }

/* ---------- Landing ---------- */
.hero { max-width: var(--maxw); margin: 0 auto; }
.eyebrow { font-family: var(--mono); font-size: 12px; letter-spacing: 2px; text-transform: uppercase; color: var(--accent-ink); margin-bottom: 12px; }
.toc-grid { display: grid; gap: 14px; margin-top: 26px; grid-template-columns: 1fr 1fr; }
@media (max-width: 640px) { .toc-grid { grid-template-columns: 1fr; } }
.toc-card {
  border: 1px solid var(--border); background: linear-gradient(160deg, var(--bg-2), rgba(18,19,31,.3));
  border-radius: var(--radius); padding: 20px; text-decoration: none; color: var(--text);
  transition: .18s; position: relative; overflow: hidden;
}
.toc-card::after {
  content: ""; position: absolute; inset: 0; border-radius: var(--radius);
  background: radial-gradient(400px 200px at var(--mx,50%) -20%, rgba(139,124,255,.14), transparent 70%);
  opacity: 0; transition: opacity .25s;
}
.toc-card:hover { border-color: var(--border-lit); transform: translateY(-3px); box-shadow: var(--glow); }
.toc-card:hover::after { opacity: 1; }
.toc-card .pt { font-family: var(--mono); font-size: 11px; color: var(--accent-ink); text-transform: uppercase; letter-spacing: .8px; }
.toc-card h3 { margin: 8px 0 4px; color: var(--text); font-size: 18px; }
.toc-card p { margin: 0; color: var(--text-dim); font-size: 14px; }
.badge { font-size: 10.5px; padding: 2px 9px; border-radius: 20px; background: var(--bg-3); color: var(--text-faint); border: 1px solid var(--border); font-family: var(--mono); }
.badge.done { color: var(--lime); border-color: var(--lime); }

/* Scroll-reveal: elements fade up as they enter view (see site.js observer) */
.reveal { opacity: 0; transform: translateY(16px); transition: opacity .6s, transform .6s; }
.reveal.in { opacity: 1; transform: none; }