/* AI Engineering Curriculum — shared lesson stylesheet
   Tufte-inspired: readable, print-friendly, returns well for review. */

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

:root {
  --text:           #1c1917;
  --text-muted:     #78716c;
  --text-light:     #a8a29e;
  --bg:             #faf8f5;
  --bg-alt:         #f0ede8;
  --bg-code:        #f5f2ee;
  --accent:         #009485;
  --accent-dark:    #007a6e;
  --success:        #16a34a;
  --success-bg:     #dcfce7;
  --warning:        #c2820a;
  --border:         #e5e0d8;
  --project-fg:     #6d28d9;
  --project-bg:     #ede9fe;
  --assignment-bg:  #f5f0e8;
  --assignment-bdr: #d5c9b5;
  --font-body:      'Inter', system-ui, -apple-system, sans-serif;
  --font-ui:        'Inter', system-ui, -apple-system, sans-serif;
  --font-mono:      'JetBrains Mono', 'Fira Code', 'Courier New', monospace;
  --width-body:     680px;
  --width-wide:     900px;
}

/* ── Dark theme ───────────────────────────────────────────────── */

html.dark {
  --text:           #e2e8f0;
  --text-muted:     #94a3b8;
  --text-light:     #64748b;
  --bg:             #1f1f1e;
  --bg-alt:         #2a2a28;
  --bg-code:        #252523;
  --accent:         #009485;
  --accent-dark:    #00c4b0;
  --success:        #4ade80;
  --success-bg:     #052e16;
  --warning:        #fbbf24;
  --border:         #3a3a38;
  --project-fg:     #a78bfa;
  --project-bg:     #1e1b4b;
  --assignment-bg:  #1a1a0e;
  --assignment-bdr: #6b5010;
}

/* ── Theme toggle ─────────────────────────────────────────────── */

.theme-toggle {
  position: fixed;
  top: 1rem;
  right: 1rem;
  width: 2.8rem;
  height: 2.8rem;
  border-radius: 8px;
  border: 1.5px solid var(--border);
  background: var(--bg-alt);
  color: var(--text-muted);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 200;
  box-shadow: 0 1px 4px rgba(0,0,0,0.10);
  transition: background 0.15s, border-color 0.15s, box-shadow 0.15s;
}

.theme-toggle:hover {
  background: var(--bg-hover, var(--border));
  color: var(--text);
  box-shadow: 0 2px 6px rgba(0,0,0,0.13);
}

/* ── Reset & base ─────────────────────────────────────────────── */

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html {
  font-size: 18px;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-body);
  font-size: 1rem;
  line-height: 1.75;
  color: var(--text);
  background: var(--bg);
  padding: 0 1.5rem;
}

/* ── Layout ───────────────────────────────────────────────────── */

.lesson-wrapper {
  max-width: var(--width-body);
  margin: 0 auto;
  padding: 3rem 0 6rem;
}

/* ── Breadcrumb ───────────────────────────────────────────────── */

.breadcrumb {
  font-family: var(--font-ui);
  font-size: 0.78rem;
  color: var(--text-light);
  margin-bottom: 2.5rem;
  letter-spacing: 0.02em;
}

.breadcrumb a {
  color: var(--text-light);
  text-decoration: none;
}

.breadcrumb a:hover { color: var(--accent); }
.breadcrumb span { margin: 0 0.4em; }

/* ── Lesson header ────────────────────────────────────────────── */

.lesson-header {
  border-bottom: 1px solid var(--border);
  margin-bottom: 2.5rem;
  padding-bottom: 1.5rem;
}

.lesson-meta {
  font-family: var(--font-ui);
  font-size: 0.8rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--accent);
  margin-bottom: 0.5rem;
}

.lesson-header h1 {
  font-size: 2rem;
  font-weight: normal;
  line-height: 1.25;
  color: var(--text);
}

/* ── Typography ───────────────────────────────────────────────── */

h2 {
  font-size: 1.35rem;
  font-weight: normal;
  margin: 2.5rem 0 0.75rem;
  color: var(--text);
  border-bottom: 1px solid var(--border);
  padding-bottom: 0.25rem;
}

h3 {
  font-size: 1.1rem;
  font-weight: bold;
  margin: 2rem 0 0.5rem;
  color: var(--text);
}

p {
  margin-bottom: 1.25rem;
}

p:last-child { margin-bottom: 0; }

a {
  color: var(--accent);
  text-decoration: underline;
  text-underline-offset: 2px;
}

a:hover { color: var(--accent-dark); }

ul, ol {
  padding-left: 1.5rem;
  margin-bottom: 1.25rem;
}

li { margin-bottom: 0.35rem; }

/* ── Interactive checklists (Markdown task lists) ─────────────────── */

ul.checklist {
  list-style: none;
  padding-left: 0;
  margin: 1.5rem 0;
  border: 1px solid var(--border);
  border-radius: 4px;
  overflow: hidden;
}

.checklist-item {
  display: flex;
  align-items: flex-start;
  gap: 0.65rem;
  margin-bottom: 0;
  padding: 0.65rem 1rem;
  border-bottom: 1px solid var(--border);
  cursor: pointer;
  transition: background 0.1s;
}

.checklist-item:last-child { border-bottom: none; }

.checklist-item:hover { background: var(--bg-alt); }

.checklist-item input[type="checkbox"] {
  margin-top: 0.2rem;
  width: 16px;
  height: 16px;
  flex-shrink: 0;
  accent-color: var(--accent);
  cursor: pointer;
}

.checklist-item.checked {
  color: var(--text-muted);
}

.checklist-item p { margin: 0; }

strong { font-weight: bold; }
em { font-style: italic; }

blockquote {
  border-left: 3px solid var(--border);
  padding: 0.25rem 0 0.25rem 1.25rem;
  margin: 1.5rem 0;
  color: var(--text-muted);
  font-style: italic;
}

/* ── Code ─────────────────────────────────────────────────────── */

code {
  font-family: var(--font-mono);
  font-size: 0.82em;
  background: var(--bg-code);
  padding: 0.1em 0.35em;
  border-radius: 3px;
  color: var(--text);
}

pre {
  background: var(--bg-code);
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: 1.25rem 1.5rem;
  overflow-x: auto;
  margin: 1.5rem 0;
  line-height: 1.5;
}

pre code {
  background: none;
  padding: 0;
  font-size: 0.85rem;
}

/* ── Tables ───────────────────────────────────────────────────── */

table {
  border-collapse: collapse;
  width: 100%;
  margin: 1.5rem 0;
  font-size: 0.9rem;
}

th {
  text-align: left;
  font-family: var(--font-ui);
  font-size: 0.78rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-muted);
  border-bottom: 2px solid var(--border);
  padding: 0.5rem 0.75rem;
}

td {
  border-bottom: 1px solid var(--border);
  padding: 0.6rem 0.75rem;
  vertical-align: top;
}

tr:last-child td { border-bottom: none; }

/* ── Lesson sections ──────────────────────────────────────────── */

.learning-outcomes {
  background: var(--bg-alt);
  border-left: 3px solid var(--accent);
  border-radius: 0 4px 4px 0;
  padding: 1.25rem 1.5rem;
  margin: 1.5rem 0 2.5rem;
}

.learning-outcomes h2 {
  font-family: var(--font-ui);
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--accent);
  border: none;
  margin: 0 0 0.75rem;
  padding: 0;
}

.learning-outcomes ul { margin-bottom: 0; }

/* ── Assignment section ───────────────────────────────────────── */

.assignment {
  background: var(--assignment-bg);
  border: 1px solid var(--assignment-bdr);
  border-radius: 4px;
  padding: 1.5rem 1.75rem;
  margin: 2.5rem 0;
}

.assignment h2 {
  font-family: var(--font-ui);
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--warning);
  border: none;
  margin: 0 0 1rem;
  padding: 0;
}

.assignment ol { margin-bottom: 0; }

.assignment li {
  margin-bottom: 0.75rem;
  padding-left: 0.25rem;
}

.assignment li:last-child { margin-bottom: 0; }

.assignment .why {
  display: block;
  font-style: italic;
  color: var(--text-muted);
  font-size: 0.9rem;
  margin-top: 0.2rem;
}

/* ── Knowledge check ──────────────────────────────────────────── */

.knowledge-check {
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: 1.5rem 1.75rem;
  margin: 2.5rem 0;
}

.kc-intro,
.lesson-desc {
  font-size: 0.9rem;
  color: var(--text-muted);
  margin-bottom: 1rem;
}

.knowledge-check h2 {
  font-family: var(--font-ui);
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
  border: none;
  margin: 0 0 1rem;
  padding: 0;
}

.knowledge-check ul {
  list-style: none;
  padding: 0;
  margin: 0;
}

.knowledge-check li { margin-bottom: 0; }

.knowledge-check details {
  border-bottom: 1px solid var(--border);
  padding: 0.6rem 0;
}

.knowledge-check details:last-child { border-bottom: none; }

.knowledge-check summary {
  cursor: pointer;
  font-size: 0.95rem;
  color: var(--text);
  list-style: none;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  user-select: none;
}

.knowledge-check summary::before {
  content: '';
  display: inline-block;
  width: 12px;
  height: 12px;
  flex-shrink: 0;
  background-color: var(--text-light);
  transition: transform 0.15s, background-color 0.15s;
  -webkit-mask: url("data:image/svg+xml,%3Csvg%20xmlns%3D'http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg'%20width%3D'12'%20height%3D'12'%20viewBox%3D'0%200%2012%2012'%20fill%3D'none'%3E%3Cpath%20d%3D'M4.5%203L7.5%206L4.5%209'%20stroke%3D'black'%20stroke-width%3D'2'%20stroke-linecap%3D'round'%20stroke-linejoin%3D'round'%2F%3E%3C%2Fsvg%3E") center/contain no-repeat;
  mask: url("data:image/svg+xml,%3Csvg%20xmlns%3D'http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg'%20width%3D'12'%20height%3D'12'%20viewBox%3D'0%200%2012%2012'%20fill%3D'none'%3E%3Cpath%20d%3D'M4.5%203L7.5%206L4.5%209'%20stroke%3D'black'%20stroke-width%3D'2'%20stroke-linecap%3D'round'%20stroke-linejoin%3D'round'%2F%3E%3C%2Fsvg%3E") center/contain no-repeat;
}

.knowledge-check details[open] summary::before {
  transform: rotate(90deg);
}

.knowledge-check .answer {
  padding: 0.5rem 0 0.25rem 1.25rem;
  font-size: 0.9rem;
  color: var(--text-muted);
}

/* ── Additional resources ─────────────────────────────────────── */

.additional-resources {
  border-top: 1px solid var(--border);
  padding-top: 1.5rem;
  margin-top: 2.5rem;
}

.additional-resources h2 {
  font-family: var(--font-ui);
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-light);
  border: none;
  margin: 0 0 0.75rem;
  padding: 0;
}

.additional-resources ul { margin-bottom: 0; }

/* ── Progress / mark-complete ─────────────────────────────────── */

.lesson-footer {
  margin-top: 3rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 1rem;
  font-family: var(--font-ui);
  font-size: 0.9rem;
}

.btn-complete {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: var(--accent);
  color: #fff;
  border: none;
  border-radius: 4px;
  padding: 0.6rem 1.25rem;
  font-family: var(--font-ui);
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.15s;
}

.btn-complete:hover { background: var(--accent-dark); }

.btn-complete.completed {
  background: var(--success);
  cursor: default;
}

.btn-complete.completed:hover { background: var(--success); }

/* ── Lesson nav (prev/next) ───────────────────────────────────── */

.lesson-nav {
  display: flex;
  justify-content: space-between;
  margin-top: 1.5rem;
  font-family: var(--font-ui);
  font-size: 0.9rem;
}

.lesson-nav a {
  color: var(--accent);
  text-decoration: none;
  display: flex;
  align-items: center;
  gap: 0.35rem;
}

.lesson-nav a:hover { color: var(--accent-dark); }

/* ── Project badge ────────────────────────────────────────────── */

.project-badge {
  display: inline-block;
  background: #dcfce7;
  color: #15803d;
  border: 1px solid #86efac;
  border-radius: 3px;
  font-family: var(--font-ui);
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  padding: 0.15em 0.55em;
  vertical-align: middle;
  margin-left: 0.4em;
}

.chapter-project-badge {
  background: #ede9fe;
  color: #6d28d9;
  border-color: #c4b5fd;
}

/* ── Callout boxes ────────────────────────────────────────────── */

.callout {
  border-left: 3px solid var(--border);
  padding: 0.75rem 1.25rem;
  margin: 1.5rem 0;
  background: var(--bg-alt);
  border-radius: 0 4px 4px 0;
  font-size: 0.95rem;
}

.callout.info  { border-color: var(--accent); }
.callout.warn  { border-color: var(--warning); }
.callout.good  { border-color: var(--success); }

/* ── Heading anchor links ─────────────────────────────────────── */

.heading-anchor {
  display: inline-flex;
  align-items: center;
  margin-left: 0.4rem;
  color: var(--text-light);
  text-decoration: none;
  opacity: 0;
  transition: opacity 0.15s;
  vertical-align: middle;
}

h2:hover .heading-anchor,
h3:hover .heading-anchor { opacity: 1; }

/* ── TOC sidebar ──────────────────────────────────────────────── */

.lesson-toc {
  position: fixed;
  top: 5rem;
  right: 1.5rem;
  width: 190px;
  max-height: calc(100vh - 7rem);
  overflow-y: auto;
  font-family: var(--font-ui);
}

.toc-label {
  font-size: 0.65rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-light);
  margin-bottom: 0.6rem;
}

.lesson-toc ul {
  list-style: none;
  padding: 0;
  margin: 0;
  border-left: 1px solid var(--border);
}

.lesson-toc li { margin: 0; }

.lesson-toc li.toc-sub { padding-left: 0.6rem; }

.lesson-toc a {
  display: block;
  padding: 0.22rem 0 0.22rem 0.7rem;
  font-size: 0.73rem;
  line-height: 1.35;
  color: var(--text-light);
  text-decoration: none;
  border-left: 2px solid transparent;
  margin-left: -1px;
  transition: color 0.1s, border-color 0.1s;
}

.lesson-toc a:hover { color: var(--text-muted); }

.lesson-toc a.active {
  color: var(--accent);
  border-left-color: var(--accent);
}

@media (max-width: 1140px) { .lesson-toc { display: none; } }

/* ── Fixed home button ────────────────────────────────────────── */

.home-btn {
  position: fixed;
  top: 1rem;
  left: 1rem;
  z-index: 200;
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  padding: 0.3rem 0.65rem;
  border-radius: 4px;
  border: 1px solid var(--border);
  background: var(--bg-alt);
  color: var(--text-muted);
  font-family: var(--font-ui);
  font-size: 0.78rem;
  font-weight: 500;
  text-decoration: none;
  cursor: pointer;
  transition: background 0.15s, color 0.15s;
}

.home-btn:hover {
  background: var(--border);
  color: var(--text);
  text-decoration: none;
}

/* ── Lesson footer note ───────────────────────────────────────── */

.lesson-footer-note {
  color: var(--text-muted);
  font-size: 0.9rem;
}

/* ── Community showcase (project pages) ──────────────────────── */

.community-showcase {
  margin-top: 3rem;
  padding-top: 2rem;
  border-top: 2px solid var(--border);
}

.community-showcase h2 {
  font-size: 1.15rem;
  font-weight: 700;
  margin-bottom: 0.4rem;
}

.community-showcase > p {
  color: var(--text-muted);
  font-size: 0.9rem;
  margin-bottom: 1.5rem;
}

/* ── Print ────────────────────────────────────────────────────── */

@media print {
  body { background: #fff; padding: 0; font-size: 11pt; }
  .lesson-wrapper { max-width: 100%; padding: 0; }
  .lesson-footer, .lesson-nav, .btn-complete { display: none; }
  a { color: var(--text); }
  a[href]::after { content: " (" attr(href) ")"; font-size: 0.8em; color: var(--text-muted); }
  pre, code { font-size: 9pt; }
  h2, h3 { page-break-after: avoid; }
  .assignment, .knowledge-check { break-inside: avoid; }
}

/* ── Responsive ───────────────────────────────────────────────── */

@media (max-width: 720px) {
  html { font-size: 16px; }
  .lesson-footer { flex-direction: column; align-items: flex-start; }
}