/* =========================================================
   Vibe Coding & Agents — Advanced Programming for Data Scientists
   Clean academic / TAU theme
   ========================================================= */

:root {
  --tau-blue: #00447c;
  --tau-blue-dark: #012d52;
  --tau-blue-light: #0067b1;
  --accent: #0067b1;
  --accent-warm: #c8102e;      /* used sparingly for "live"/challenge cues */
  --ink: #1c2530;
  --ink-soft: #495667;
  --muted: #6b7787;
  --line: #e2e8f0;
  --line-strong: #cbd5e1;
  --bg: #ffffff;
  --bg-soft: #f6f8fb;
  --bg-tint: #eef4fa;
  --code-bg: #0f2233;
  --code-ink: #e6edf3;
  --good: #1a7f4b;
  --good-bg: #e8f6ee;
  --warn: #9a6700;
  --warn-bg: #fff8e6;
  --radius: 12px;
  --radius-sm: 8px;
  --shadow: 0 1px 3px rgba(16, 42, 67, .08), 0 8px 24px rgba(16, 42, 67, .06);
  --shadow-soft: 0 1px 2px rgba(16, 42, 67, .06);
  --serif: Georgia, "Times New Roman", "Iowan Old Style", serif;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --mono: "SF Mono", "JetBrains Mono", "Fira Code", ui-monospace, Menlo, Consolas, monospace;
  --maxw: 960px;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: var(--sans);
  color: var(--ink);
  background: var(--bg);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

/* ---------- Top navigation ---------- */
.nav {
  position: sticky;
  top: 0;
  z-index: 50;
  background: rgba(255, 255, 255, .92);
  backdrop-filter: saturate(1.4) blur(8px);
  border-bottom: 1px solid var(--line);
}
.nav-inner {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: .55rem 1.25rem;
  display: flex;
  align-items: center;
  gap: 1.25rem;
  flex-wrap: wrap;
}
.nav-brand {
  font-family: var(--serif);
  font-weight: 700;
  color: var(--tau-blue);
  text-decoration: none;
  font-size: 1.02rem;
  white-space: nowrap;
  display: flex;
  align-items: center;
  gap: .5rem;
}
.nav-brand .mark {
  display: inline-grid;
  place-items: center;
  width: 26px; height: 26px;
  border-radius: 7px;
  background: var(--tau-blue);
  color: #fff;
  font-family: var(--mono);
  font-size: .8rem;
  font-weight: 700;
}
.nav-links {
  display: flex;
  gap: .35rem;
  margin-left: auto;
  flex-wrap: wrap;
}
.nav-links a {
  text-decoration: none;
  color: var(--ink-soft);
  font-size: .86rem;
  padding: .35rem .6rem;
  border-radius: 999px;
  white-space: nowrap;
  transition: background .15s, color .15s;
}
.nav-links a:hover { background: var(--bg-tint); color: var(--tau-blue); }
.nav-links a.active {
  background: var(--tau-blue);
  color: #fff;
}
.nav-links a .step-num {
  font-family: var(--mono);
  opacity: .65;
  font-size: .78em;
  margin-right: .25rem;
}

/* ---------- Layout ---------- */
main { max-width: var(--maxw); margin: 0 auto; padding: 0 1.25rem 5rem; }

.hero {
  padding: 3rem 0 2rem;
  border-bottom: 1px solid var(--line);
  margin-bottom: 2.5rem;
}
.eyebrow {
  font-family: var(--mono);
  font-size: .74rem;
  letter-spacing: .12em;
  text-transform: uppercase;
  color: var(--accent);
  margin: 0 0 .75rem;
  display: flex;
  align-items: center;
  gap: .6rem;
}
.eyebrow .pill {
  background: var(--bg-tint);
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: .15rem .55rem;
  color: var(--ink-soft);
  letter-spacing: .06em;
}
h1 {
  font-family: var(--serif);
  font-size: clamp(1.9rem, 4.5vw, 2.9rem);
  line-height: 1.12;
  margin: 0 0 .6rem;
  color: var(--tau-blue-dark);
  letter-spacing: -.01em;
}
.hero p.lead {
  font-size: 1.12rem;
  color: var(--ink-soft);
  max-width: 60ch;
  margin: 0;
}

h2 {
  font-family: var(--serif);
  font-size: 1.6rem;
  margin: 2.75rem 0 .5rem;
  color: var(--tau-blue-dark);
  scroll-margin-top: 70px;
}
h3 {
  font-size: 1.15rem;
  margin: 1.75rem 0 .4rem;
  color: var(--ink);
}
h2 + p, h3 + p { margin-top: .35rem; }
p { margin: .6rem 0; }
a { color: var(--accent); }
a:hover { color: var(--tau-blue); }

.section-lead { color: var(--muted); font-size: 1.02rem; max-width: 62ch; }

/* ---------- Cards & panels ---------- */
.card {
  background: var(--bg);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 1.4rem 1.5rem;
  box-shadow: var(--shadow-soft);
  margin: 1.1rem 0;
}
.grid {
  display: grid;
  gap: 1rem;
  grid-template-columns: repeat(auto-fit, minmax(230px, 1fr));
}
.grid.two { grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); }

.mini-card {
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  padding: 1.1rem 1.2rem;
  background: var(--bg-soft);
}
.mini-card h3 { margin-top: 0; font-size: 1.02rem; }
.mini-card .icon {
  font-size: 1.4rem;
  display: block;
  margin-bottom: .4rem;
}

/* ---------- Steps ---------- */
.steps { counter-reset: step; padding: 0; margin: 1.5rem 0; list-style: none; }
.steps > li {
  position: relative;
  padding: 1.2rem 1.3rem 1.2rem 3.6rem;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  margin-bottom: .9rem;
  background: var(--bg);
  box-shadow: var(--shadow-soft);
}
.steps > li::before {
  counter-increment: step;
  content: counter(step);
  position: absolute;
  left: 1.1rem;
  top: 1.15rem;
  width: 1.8rem; height: 1.8rem;
  background: var(--tau-blue);
  color: #fff;
  border-radius: 50%;
  display: grid;
  place-items: center;
  font-family: var(--mono);
  font-weight: 700;
  font-size: .9rem;
}
.steps > li h3 { margin: 0 0 .3rem; font-size: 1.08rem; }
.steps > li p { margin: .3rem 0; color: var(--ink-soft); }
.steps > li p:last-child { margin-bottom: 0; }

/* ---------- Interactive checklist ---------- */
.checklist { list-style: none; padding: 0; margin: 1.25rem 0; }
.checklist li {
  display: flex;
  align-items: flex-start;
  gap: .75rem;
  padding: .85rem 1rem;
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  margin-bottom: .55rem;
  cursor: pointer;
  transition: background .15s, border-color .15s;
  user-select: none;
}
.checklist li:hover { background: var(--bg-soft); }
.checklist li.done { background: var(--good-bg); border-color: #bfe6cd; }
.checklist li.done .cl-text { color: var(--good); text-decoration: line-through; }
.checklist .box {
  flex: 0 0 auto;
  width: 22px; height: 22px;
  border: 2px solid var(--line-strong);
  border-radius: 6px;
  display: grid;
  place-items: center;
  margin-top: 2px;
  color: #fff;
  font-size: .8rem;
  transition: background .15s, border-color .15s;
}
.checklist li.done .box { background: var(--good); border-color: var(--good); }
.checklist .cl-text { flex: 1; }
.checklist .cl-text small { display: block; color: var(--muted); font-weight: 400; }
.checklist-progress {
  font-family: var(--mono);
  font-size: .85rem;
  color: var(--muted);
  margin: .5rem 0 1rem;
}
.reset-btn {
  background: none; border: 1px solid var(--line-strong);
  color: var(--ink-soft); border-radius: 999px;
  padding: .2rem .7rem; font-size: .78rem; cursor: pointer;
  margin-left: .5rem;
}
.reset-btn:hover { background: var(--bg-soft); }

/* ---------- Code blocks ---------- */
pre, code { font-family: var(--mono); }
code.inline {
  background: var(--bg-tint);
  border: 1px solid var(--line);
  border-radius: 5px;
  padding: .08em .38em;
  font-size: .88em;
  color: var(--tau-blue-dark);
}
.codeblock {
  background: var(--code-bg);
  border-radius: var(--radius-sm);
  margin: 1rem 0;
  overflow: hidden;
  border: 1px solid #1c3348;
}
.codeblock .cb-head {
  display: flex;
  align-items: center;
  gap: .5rem;
  padding: .5rem .9rem;
  background: #0b1a28;
  border-bottom: 1px solid #1c3348;
}
.codeblock .cb-dot { width: 11px; height: 11px; border-radius: 50%; }
.cb-dot.r { background: #ff5f56; } .cb-dot.y { background: #ffbd2e; } .cb-dot.g { background: #27c93f; }
.codeblock .cb-name {
  margin-left: .5rem;
  font-family: var(--mono);
  font-size: .78rem;
  color: #7d93a8;
}
.codeblock pre {
  margin: 0;
  padding: 1rem 1.15rem;
  overflow-x: auto;
  font-size: .84rem;
  line-height: 1.6;
  color: var(--code-ink);
}
/* lightweight syntax tint (injected via data-t so no attr word collides
   with a Python keyword during highlighting) */
[data-t=kw]  { color: #ff7b9c; }
[data-t=str] { color: #9ae6b4; }
[data-t=com] { color: #6b8299; font-style: italic; }
[data-t=num] { color: #f0b866; }

/* ---------- Chat / prompt walkthrough ---------- */
.chat { margin: 1.5rem 0; }
.bubble {
  border-radius: 14px;
  padding: .9rem 1.1rem;
  margin: .7rem 0;
  max-width: 88%;
  box-shadow: var(--shadow-soft);
}
.bubble .who {
  font-size: .72rem;
  font-family: var(--mono);
  letter-spacing: .05em;
  text-transform: uppercase;
  margin-bottom: .35rem;
  opacity: .7;
}
.bubble.you {
  background: var(--tau-blue);
  color: #fff;
  margin-left: auto;
  border-bottom-right-radius: 4px;
}
.bubble.you .who { color: #cfe4f7; }
.bubble.you code.inline { background: rgba(255,255,255,.16); border-color: rgba(255,255,255,.25); color: #eaf3fb; }
.bubble.ai {
  background: var(--bg-soft);
  border: 1px solid var(--line);
  border-bottom-left-radius: 4px;
}
.bubble.ai .who { color: var(--accent); }
.bubble p:first-child { margin-top: 0; }
.bubble p:last-child { margin-bottom: 0; }

.turn-label {
  font-family: var(--mono);
  font-size: .74rem;
  letter-spacing: .08em;
  text-transform: uppercase;
  color: var(--accent);
  margin: 1.8rem 0 .2rem;
  display: flex;
  align-items: center;
  gap: .5rem;
}
.turn-label::before {
  content: "";
  width: 1.4rem; height: 2px;
  background: var(--accent);
}

/* ---------- Callouts ---------- */
.callout {
  border-left: 4px solid var(--accent);
  background: var(--bg-tint);
  padding: .9rem 1.1rem;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  margin: 1.1rem 0;
}
.callout.tip { border-color: var(--good); background: var(--good-bg); }
.callout.warn { border-color: var(--warn); background: var(--warn-bg); }
.callout.live { border-color: var(--accent-warm); background: #fdecef; }
.callout .c-title {
  font-weight: 700;
  display: flex;
  align-items: center;
  gap: .45rem;
  margin-bottom: .2rem;
}
.callout p { margin: .25rem 0; }

/* ---------- Badges ---------- */
.badge {
  display: inline-block;
  font-family: var(--mono);
  font-size: .72rem;
  padding: .2rem .55rem;
  border-radius: 999px;
  background: var(--bg-tint);
  color: var(--tau-blue);
  border: 1px solid var(--line);
  letter-spacing: .03em;
}
.badge.warm { background: #fdecef; color: var(--accent-warm); border-color: #f5c6ce; }
.badge.time { background: var(--warn-bg); color: var(--warn); border-color: #f0e0a8; }
.badge.hw { background: #efeafc; color: #5b3ec8; border-color: #ddd2f5; }

/* ---------- Bit visualizer ---------- */
.bitviz { margin: 1.25rem 0; }
.bitviz .controls {
  display: flex;
  align-items: center;
  gap: .75rem;
  flex-wrap: wrap;
  margin-bottom: 1rem;
}
.bitviz label { font-size: .85rem; color: var(--ink-soft); font-weight: 600; }
.bitviz input[type=number], .bitviz input[type=text] {
  font-family: var(--mono);
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-sm);
  padding: .45rem .6rem;
  font-size: .95rem;
  width: 130px;
}
.bitviz input:focus { outline: 2px solid var(--accent); border-color: var(--accent); }
.bits {
  display: flex;
  flex-wrap: wrap;
  gap: 5px;
  font-family: var(--mono);
}
.bit {
  width: 34px; height: 40px;
  display: grid;
  place-items: center;
  border-radius: 7px;
  border: 1px solid var(--line);
  background: var(--bg-soft);
  color: var(--muted);
  font-weight: 700;
  font-size: 1rem;
  position: relative;
  transition: background .2s, color .2s, transform .2s;
}
.bit.one { background: var(--tau-blue); color: #fff; border-color: var(--tau-blue); }
.bit.run { background: var(--accent-warm); border-color: var(--accent-warm); color: #fff; transform: translateY(-3px); }
.bit .idx {
  position: absolute;
  bottom: -18px;
  font-size: .6rem;
  color: var(--muted);
  font-weight: 400;
}
.bitviz .readout {
  font-family: var(--mono);
  font-size: .9rem;
  color: var(--ink-soft);
  margin-top: 1.75rem;
  background: var(--bg-soft);
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  padding: .7rem .9rem;
}
.bitviz .readout b { color: var(--tau-blue); }
.arrow-row { text-align: center; color: var(--muted); font-size: 1.3rem; margin: .4rem 0; }

/* ---------- Countdown timer ---------- */
.timer-card {
  background: linear-gradient(135deg, var(--tau-blue-dark), var(--tau-blue));
  color: #fff;
  border-radius: var(--radius);
  padding: 1.6rem;
  text-align: center;
  box-shadow: var(--shadow);
}
.timer-display {
  font-family: var(--mono);
  font-size: clamp(3rem, 12vw, 5.5rem);
  font-weight: 700;
  letter-spacing: .04em;
  line-height: 1;
  margin: .4rem 0;
}
.timer-display.warning { color: #ffd166; }
.timer-display.danger { color: #ff8a8a; animation: pulse 1s infinite; }
@keyframes pulse { 50% { opacity: .55; } }
.timer-controls { display: flex; gap: .6rem; justify-content: center; flex-wrap: wrap; margin-top: .6rem; }
.timer-btn {
  font-family: var(--sans);
  border: 1px solid rgba(255,255,255,.4);
  background: rgba(255,255,255,.1);
  color: #fff;
  padding: .5rem 1.2rem;
  border-radius: 999px;
  font-size: .9rem;
  cursor: pointer;
  font-weight: 600;
  transition: background .15s;
}
.timer-btn:hover { background: rgba(255,255,255,.22); }
.timer-btn.primary { background: #fff; color: var(--tau-blue-dark); border-color: #fff; }
.timer-label { font-size: .8rem; text-transform: uppercase; letter-spacing: .12em; opacity: .8; }

/* ---------- Tables ---------- */
.table-wrap { overflow-x: auto; margin: 1.1rem 0; }
table {
  border-collapse: collapse;
  width: 100%;
  font-size: .9rem;
  min-width: 480px;
}
th, td { text-align: left; padding: .65rem .8rem; border-bottom: 1px solid var(--line); }
th { background: var(--bg-soft); color: var(--tau-blue-dark); font-weight: 700; }
tbody tr:hover { background: var(--bg-soft); }
td code { font-size: .85em; }

/* ---------- Comparison two-col ---------- */
.vs {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 1rem;
  align-items: stretch;
  margin: 1.25rem 0;
}
.vs .col { border: 1px solid var(--line); border-radius: var(--radius); padding: 1.1rem 1.2rem; }
.vs .col.bad { background: #fdf3f4; border-color: #f2d0d5; }
.vs .col.good { background: var(--good-bg); border-color: #bfe6cd; }
.vs .col h4 { margin: 0 0 .6rem; font-size: 1rem; }
.vs .mid { display: grid; place-items: center; font-family: var(--serif); font-style: italic; color: var(--muted); }
.vs ul { margin: .3rem 0; padding-left: 1.1rem; }
.vs li { margin: .3rem 0; font-size: .9rem; }
@media (max-width: 640px) {
  .vs { grid-template-columns: 1fr; }
  .vs .mid { padding: .3rem; }
}

/* ---------- Flow diagram ---------- */
.flow {
  display: flex;
  align-items: center;
  gap: .5rem;
  flex-wrap: wrap;
  margin: 1.25rem 0;
  justify-content: center;
}
.flow .node {
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-sm);
  padding: .7rem 1rem;
  background: var(--bg);
  text-align: center;
  font-size: .85rem;
  min-width: 96px;
  box-shadow: var(--shadow-soft);
}
.flow .node.hl { background: var(--tau-blue); color: #fff; border-color: var(--tau-blue); }
.flow .node small { display: block; color: var(--muted); font-size: .7rem; }
.flow .node.hl small { color: #cfe4f7; }
.flow .conn { color: var(--accent); font-size: 1.4rem; font-weight: 700; }

/* ---------- Progress rail (page 4) ---------- */
.rail { list-style: none; padding: 0; margin: 1.5rem 0; position: relative; }
.rail::before {
  content: ""; position: absolute; left: 15px; top: 8px; bottom: 8px;
  width: 2px; background: var(--line);
}
.rail > li { position: relative; padding: 0 0 1.6rem 3rem; }
.rail > li::before {
  content: ""; position: absolute; left: 8px; top: 4px;
  width: 16px; height: 16px; border-radius: 50%;
  background: #fff; border: 3px solid var(--accent);
}
.rail > li h3 { margin: 0 0 .3rem; }
.rail .lvl {
  font-family: var(--mono); font-size: .72rem; color: var(--accent);
  letter-spacing: .05em; text-transform: uppercase;
}

/* ---------- Buttons / links ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  gap: .45rem;
  background: var(--tau-blue);
  color: #fff;
  text-decoration: none;
  padding: .6rem 1.2rem;
  border-radius: 999px;
  font-weight: 600;
  font-size: .92rem;
  transition: background .15s, transform .1s;
  box-shadow: var(--shadow-soft);
}
.btn:hover { background: var(--tau-blue-dark); color: #fff; transform: translateY(-1px); }
.btn.ghost { background: transparent; color: var(--tau-blue); border: 1px solid var(--line-strong); box-shadow: none; }
.btn.ghost:hover { background: var(--bg-soft); }
.btn-row { display: flex; gap: .7rem; flex-wrap: wrap; margin: 1.25rem 0; }

/* ---------- Page footer nav ---------- */
.page-nav {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 3rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--line);
  flex-wrap: wrap;
}
.page-nav a {
  text-decoration: none;
  color: var(--ink-soft);
  font-size: .9rem;
  display: flex;
  flex-direction: column;
  padding: .6rem 1rem;
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  min-width: 180px;
}
.page-nav a:hover { border-color: var(--accent); background: var(--bg-soft); }
.page-nav a span { font-size: .72rem; color: var(--muted); font-family: var(--mono); }
.page-nav a.next { text-align: right; margin-left: auto; }

/* locked (not yet released) nav links */
.nav-links a.locked, .page-nav a.locked {
  opacity: .4;
  pointer-events: none;
  cursor: not-allowed;
}

.footer {
  text-align: center;
  color: var(--muted);
  font-size: .82rem;
  padding: 2rem 1.25rem 3rem;
  border-top: 1px solid var(--line);
}

/* ---------- Architecture mini-diagrams ---------- */
.arch { margin: .8rem 0 .4rem; }
.arch-row {
  display: flex; gap: .55rem; justify-content: center; align-items: stretch;
  flex-wrap: wrap; margin: .3rem 0;
}
.arch-node {
  border: 1px solid var(--line-strong); border-radius: 9px;
  padding: .5rem .8rem; background: #fff; font-size: .84rem; font-weight: 600;
  text-align: center; box-shadow: var(--shadow-soft); min-width: 92px;
  display: flex; flex-direction: column; justify-content: center;
}
.arch-node small { display: block; color: var(--muted); font-size: .68rem; font-weight: 400; margin-top: .1rem; }
.arch-node.boss { background: var(--tau-blue); color: #fff; border-color: var(--tau-blue); }
.arch-node.boss small { color: #cfe4f7; }
.arch-node.spec { background: var(--bg-tint); }
.arch-node.crit { background: #fdf3f4; border-color: #f2d0d5; }
.arch-node.out { background: var(--good-bg); border-color: #bfe6cd; }
.arch-conn { display: flex; align-items: center; color: var(--accent); font-size: 1.15rem; padding: 0 .1rem; }
.arch-down { text-align: center; color: var(--accent); font-size: 1.1rem; line-height: 1; margin: .1rem 0; }
.arch-cap { text-align: center; font-size: .76rem; color: var(--muted); font-family: var(--mono); margin-top: .35rem; }
.arch-card h3 { margin-top: 0; display: flex; align-items: center; gap: .5rem; flex-wrap: wrap; }
.arch-card .use { font-size: .86rem; color: var(--ink-soft); margin: .5rem 0 0; }
.arch-card .use b { color: var(--tau-blue-dark); }

/* nav "present" link */
.nav-links a.present { background: var(--tau-blue-dark); color: #fff; }
.nav-links a.present:hover { background: #011f3a; color: #fff; }

/* ---------- Utility ---------- */
.small { font-size: .85rem; color: var(--muted); }
.center { text-align: center; }
.tag-list { display: flex; gap: .5rem; flex-wrap: wrap; margin: .6rem 0; }
hr.soft { border: none; border-top: 1px solid var(--line); margin: 2.5rem 0; }
details { border: 1px solid var(--line); border-radius: var(--radius-sm); padding: .4rem 1rem; margin: .8rem 0; background: var(--bg-soft); }
details summary { cursor: pointer; font-weight: 600; color: var(--tau-blue); padding: .4rem 0; }
details[open] summary { margin-bottom: .4rem; }

@media (max-width: 560px) {
  .nav-brand span.full { display: none; }
  .bit { width: 28px; height: 34px; font-size: .85rem; }
}