/* ============================================
   Learn — AI engineering curriculum
   Component system for the /learn section.
   Loaded alongside style.css (which provides
   base, nav, footer, and design tokens).
   ============================================ */

:root {
  --learn-read-w: 720px;
  --learn-accent-2: #7c3aed;     /* secondary accent for track variety */
  --learn-good: #15803d;
  --learn-good-bg: #f0fdf4;
  --learn-warn: #b45309;
  --learn-warn-bg: #fffbeb;
  --learn-soon: #6c6c67;
  --learn-soon-bg: #f1f1ee;
}

/* --- Reading column -------------------------------------- */
.learn-page {
  max-width: var(--learn-read-w);
  margin: 0 auto;
  padding: 0 24px;
}

/* --- Lesson / course header ----------------------------- */
.learn-header {
  padding: 48px 0 32px;
  border-bottom: 1px solid var(--color-border-light);
  margin-bottom: 40px;
}

.learn-kicker {
  font-size: 12px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.09em;
  color: var(--color-accent);
  margin-bottom: 12px;
}

.learn-header h1 {
  font-size: 34px;
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.15;
  margin-bottom: 16px;
}

.learn-lead {
  font-size: 18px;
  line-height: 1.6;
  color: var(--color-text-2);
  max-width: 620px;
}

/* breadcrumb back to course / hub */
.learn-crumbs {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 13px;
  color: var(--color-text-3);
  margin-bottom: 20px;
}
.learn-crumbs a { color: var(--color-text-3); }
.learn-crumbs a:hover { color: var(--color-accent); text-decoration: none; }
.learn-crumbs span { color: var(--color-border); }
.learn-crumbs span:last-child { color: var(--color-text); font-weight: 600; }

/* --- Lesson body prose ---------------------------------- */
.learn-body {
  font-size: 17px;
  line-height: 1.75;
  color: var(--color-text);
}

.learn-body section { margin-bottom: 40px; }

.learn-body h2 {
  font-size: 24px;
  font-weight: 800;
  letter-spacing: -0.02em;
  line-height: 1.25;
  margin: 0 0 16px;
}

.learn-body h3 {
  font-size: 19px;
  font-weight: 700;
  letter-spacing: -0.01em;
  margin: 28px 0 10px;
}

.learn-body p { margin: 0 0 16px; }
.learn-body p:last-child { margin-bottom: 0; }
.learn-body strong { font-weight: 700; }
.learn-body a { color: var(--color-accent); text-underline-offset: 3px; }

.learn-body ul,
.learn-body ol { padding-left: 1.5em; margin: 0 0 16px; }
.learn-body ul { list-style: disc; }
.learn-body ol { list-style: decimal; }
.learn-body li { margin: 6px 0; }

/* inline + small code snippets only (no runnable blocks) */
.learn-body code {
  font-family: var(--font-mono);
  font-size: 0.85em;
  background: var(--color-code-bg);
  color: #b5246b;
  padding: 2px 6px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--color-border-light);
}

.learn-body pre {
  background: var(--color-pre-bg);
  color: var(--color-pre-text);
  border-radius: var(--radius-md);
  padding: 16px 20px;
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: 13.5px;
  line-height: 1.6;
  margin: 0 0 16px;
}
.learn-body pre code {
  background: none; color: inherit; padding: 0; border: 0; font-size: inherit;
}
.snippet-label {
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--color-text-3);
  margin-bottom: 6px;
}

/* --- Key idea box --------------------------------------- */
.key-idea {
  border: 1px solid var(--color-border);
  border-left: 4px solid var(--color-accent);
  background: var(--color-surface);
  border-radius: var(--radius-md);
  padding: 18px 22px;
  margin: 24px 0;
}
.key-idea .key-idea-label {
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--color-accent);
  margin-bottom: 8px;
}
.key-idea p { margin: 0; font-size: 16px; }

/* --- Notes / callouts (variants) ------------------------ */
.note {
  border-radius: var(--radius-md);
  padding: 16px 20px;
  margin: 24px 0;
  font-size: 15.5px;
  line-height: 1.65;
  border: 1px solid;
}
.note p:last-child { margin-bottom: 0; }
.note .note-label {
  font-weight: 700;
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin-bottom: 6px;
  display: block;
}
.note.info { background: var(--color-accent-bg); border-color: #bfdbfe; color: #1e3a8a; }
.note.info .note-label { color: #1d4ed8; }
.note.tip  { background: var(--learn-good-bg); border-color: #bbf7d0; color: #14532d; }
.note.tip .note-label  { color: var(--learn-good); }
.note.warn { background: var(--learn-warn-bg); border-color: #fde68a; color: #78350f; }
.note.warn .note-label { color: var(--learn-warn); }

/* the engineering-angle box: our differentiator, called out */
.note.eng { background: #fafaf9; border-color: var(--color-border); color: var(--color-text); }
.note.eng .note-label { color: var(--learn-accent-2); }

/* --- Figures -------------------------------------------- */
.learn-figure {
  margin: 28px 0;
}
.learn-figure .frame {
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-bg);
  padding: 20px;
  overflow: hidden;
}
.learn-figure svg { display: block; width: 100%; height: auto; }
.learn-figure figcaption {
  font-size: 13px;
  color: var(--color-text-3);
  text-align: center;
  margin-top: 10px;
}

/* --- Curated resource card ------------------------------ */
.resource-card {
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 18px 20px;
  margin: 24px 0;
  background: var(--color-bg);
}
.resource-card .resource-kind {
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  color: var(--learn-accent-2);
  margin-bottom: 8px;
}
.resource-card .resource-title {
  font-size: 17px;
  font-weight: 700;
  letter-spacing: -0.01em;
  margin-bottom: 2px;
}
.resource-card .resource-title a { color: var(--color-text); }
.resource-card .resource-title a:hover { color: var(--color-accent); text-decoration: none; }
.resource-card .resource-by { font-size: 13px; color: var(--color-text-3); margin-bottom: 12px; }
.resource-card .resource-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 8px 16px;
  font-size: 14px;
}
.resource-card dt {
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 2px;
}
.resource-card .covers dt { color: var(--learn-good); }
.resource-card .skips dt { color: var(--learn-warn); }
.resource-card dd { color: var(--color-text-2); line-height: 1.55; }
@media (max-width: 560px) { .resource-card .resource-grid { grid-template-columns: 1fr; } }

/* --- Checkpoint ----------------------------------------- */
.checkpoint {
  border-top: 2px solid var(--color-text);
  padding-top: 22px;
  margin: 48px 0 0;
}
.checkpoint h2 { font-size: 20px; margin-bottom: 12px; }
.checkpoint ul { padding-left: 1.4em; }
.checkpoint li { margin: 8px 0; color: var(--color-text-2); }

/* --- Quiz (rendered by <quiz-card>) --------------------- */
.quiz {
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 20px 22px;
  margin: 20px 0;
  background: var(--color-surface);
}
.quiz .quiz-q { font-weight: 700; font-size: 16px; margin-bottom: 14px; }
.quiz .quiz-options { display: flex; flex-direction: column; gap: 8px; }
.quiz button.quiz-opt {
  text-align: left;
  font: inherit;
  font-size: 15px;
  padding: 11px 14px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  background: var(--color-bg);
  color: var(--color-text);
  cursor: pointer;
  transition: border-color 0.12s, background 0.12s;
}
.quiz button.quiz-opt:hover:not(:disabled) { border-color: var(--color-accent); }
.quiz button.quiz-opt:disabled { cursor: default; }
.quiz button.quiz-opt.correct {
  border-color: var(--learn-good); background: var(--learn-good-bg); color: var(--learn-good);
  font-weight: 600;
}
.quiz button.quiz-opt.wrong {
  border-color: #dc2626; background: #fef2f2; color: #b91c1c;
}
.quiz .quiz-feedback {
  margin-top: 12px;
  font-size: 14px;
  line-height: 1.55;
  color: var(--color-text-2);
  min-height: 1px;
}

/* --- Reveal (rendered by <reveal>) ---------------------- */
.reveal {
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  margin: 20px 0;
  overflow: hidden;
}
.reveal > .reveal-summary {
  cursor: pointer;
  padding: 14px 18px;
  font-weight: 600;
  font-size: 15px;
  display: flex;
  align-items: center;
  gap: 10px;
  background: var(--color-surface);
  user-select: none;
}
.reveal > .reveal-summary::before {
  content: "+";
  font-family: var(--font-mono);
  color: var(--color-accent);
  font-weight: 700;
}
.reveal.open > .reveal-summary::before { content: "−"; }
.reveal > .reveal-content {
  padding: 0 18px;
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.2s ease, padding 0.2s ease;
}
.reveal.open > .reveal-content { padding: 16px 18px; max-height: 1500px; }

/* --- Video embed (rendered by <video-embed>) ------------ */
.video-embed { margin: 24px 0; }
.video-embed .ve-frame {
  position: relative;
  aspect-ratio: 16 / 9;
  border-radius: var(--radius-md);
  overflow: hidden;
  background: #111;
  cursor: pointer;
  border: 1px solid var(--color-border);
}
.video-embed .ve-frame img { width: 100%; height: 100%; object-fit: cover; opacity: 0.85; }
.video-embed .ve-frame iframe { width: 100%; height: 100%; border: 0; display: block; }
.video-embed .ve-play {
  position: absolute; inset: 0; margin: auto;
  width: 64px; height: 64px;
  display: flex; align-items: center; justify-content: center;
  background: rgba(0,0,0,0.6); border-radius: 50%;
  pointer-events: none;
}
.video-embed .ve-play::before {
  content: ""; border-style: solid; border-width: 11px 0 11px 18px;
  border-color: transparent transparent transparent #fff; margin-left: 4px;
}
.video-embed .ve-meta { margin-top: 8px; font-size: 13px; color: var(--color-text-3); }
.video-embed .ve-meta strong { color: var(--color-text-2); font-weight: 600; }

/* --- Lesson footer nav ---------------------------------- */
.lesson-nav {
  display: flex;
  align-items: stretch;
  gap: 12px;
  margin: 48px 0 80px;
  border-top: 1px solid var(--color-border-light);
  padding-top: 28px;
}
.lesson-nav a {
  flex: 1;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 14px 16px;
  text-decoration: none;
  color: inherit;
  transition: border-color 0.12s, background 0.12s;
}
.lesson-nav a:hover { border-color: var(--color-accent); background: var(--color-surface); text-decoration: none; }
.lesson-nav .dir { font-size: 12px; color: var(--color-text-3); margin-bottom: 4px; }
.lesson-nav .ttl { font-size: 15px; font-weight: 600; color: var(--color-text); letter-spacing: -0.01em; }
.lesson-nav a.next { text-align: right; }
.lesson-nav a.disabled { opacity: 0.4; pointer-events: none; }

/* ========================================================
   COURSE INDEX PAGE
   ======================================================== */
.course-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 18px;
  font-size: 13px;
  color: var(--color-text-3);
  margin-top: 16px;
}
.course-meta span { display: inline-flex; align-items: center; gap: 6px; }

.lesson-list { display: flex; flex-direction: column; gap: 0; margin: 8px 0 40px; }
.lesson-list-item {
  display: flex;
  align-items: baseline;
  gap: 18px;
  padding: 20px 0;
  border-bottom: 1px solid var(--color-border-light);
  text-decoration: none;
  color: inherit;
}
.lesson-list-item:hover { text-decoration: none; }
.lesson-list-item:hover .lli-title { color: var(--color-accent); }
.lesson-list-item .lli-num {
  font-family: var(--font-mono);
  font-size: 13px;
  color: var(--color-text-3);
  flex-shrink: 0;
  width: 26px;
}
.lesson-list-item .lli-title { font-size: 18px; font-weight: 700; letter-spacing: -0.01em; line-height: 1.3; margin-bottom: 4px; transition: color 0.12s; }
.lesson-list-item .lli-desc { font-size: 14.5px; color: var(--color-text-2); line-height: 1.55; }
.lesson-list-item.soon { pointer-events: none; }
.lesson-list-item.soon .lli-title { color: var(--color-text-3); }
.lli-soon-badge {
  font-size: 11px; font-weight: 600; color: var(--learn-soon);
  background: var(--learn-soon-bg); padding: 2px 8px; border-radius: 100px;
  margin-left: 8px; white-space: nowrap;
}

/* ========================================================
   CURRICULUM HUB
   ======================================================== */
.hub-hero {
  padding: 64px 0 40px;
  border-bottom: 1px solid var(--color-border-light);
  margin-bottom: 48px;
}
.hub-hero h1 {
  font-size: 38px; font-weight: 800; letter-spacing: -0.03em; line-height: 1.1; margin-bottom: 16px;
}
.hub-hero p { font-size: 18px; line-height: 1.6; color: var(--color-text-2); max-width: 640px; }
.hub-hero .hub-note { font-size: 14px; color: var(--color-text-3); margin-top: 16px; max-width: 640px; }

.track { margin-bottom: 52px; }
.track-head { display: flex; align-items: baseline; gap: 14px; margin-bottom: 6px; }
.track-num {
  font-family: var(--font-mono); font-size: 13px; font-weight: 600;
  color: var(--color-bg); background: var(--color-text);
  width: 26px; height: 26px; border-radius: 6px;
  display: inline-flex; align-items: center; justify-content: center; flex-shrink: 0;
}
.track-head h2 { font-size: 24px; font-weight: 800; letter-spacing: -0.02em; }
.track-intro { font-size: 15px; color: var(--color-text-2); margin: 0 0 20px 40px; max-width: 620px; }

.course-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 14px;
  margin-left: 40px;
}
.course-card {
  display: flex;
  flex-direction: column;
  gap: 8px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 18px;
  background: var(--color-bg);
  text-decoration: none;
  color: inherit;
  transition: border-color 0.12s, background 0.12s, transform 0.12s;
}
.course-card.live:hover { border-color: var(--color-accent); background: var(--color-surface); text-decoration: none; transform: translateY(-2px); }
.course-card.soon { background: var(--color-surface); border-style: dashed; cursor: default; }
.course-card-top { display: flex; align-items: flex-start; justify-content: space-between; gap: 10px; }
.course-card h3 { font-size: 17px; font-weight: 700; letter-spacing: -0.01em; line-height: 1.3; }
.course-card p { font-size: 14px; color: var(--color-text-2); line-height: 1.55; }
.course-card .course-foot { font-size: 12px; color: var(--color-text-3); margin-top: auto; padding-top: 4px; }

.status {
  font-size: 11px; font-weight: 600; padding: 2px 9px; border-radius: 100px; white-space: nowrap; flex-shrink: 0;
}
.status.live { color: var(--learn-good); background: var(--learn-good-bg); }
.status.soon { color: var(--learn-soon); background: var(--learn-soon-bg); }

@media (max-width: 640px) {
  .hub-hero h1 { font-size: 28px; }
  .hub-hero { padding: 44px 0 32px; }
  .track-intro, .course-grid { margin-left: 0; }
  .learn-header h1 { font-size: 27px; }
  .learn-lead { font-size: 16px; }
  .lesson-nav { flex-direction: column; }
}