/* ═══════════════════════════════════════════════════════════════════════════
   PHYSICSFORUM.ORG — LEARN SECTION STYLES
   ═══════════════════════════════════════════════════════════════════════════ */

/* ── Learn Hero ── */
.learn-hero {
  background: var(--color-space-navy);
  padding: var(--space-24) 0 var(--space-16);
  text-align: center;
  position: relative;
  overflow: hidden;
}
.learn-hero::before {
  content: '';
  position: absolute;
  top: -50%;
  left: -50%;
  width: 200%;
  height: 200%;
  background: radial-gradient(circle at 30% 40%, rgba(37,99,235,0.08) 0%, transparent 50%),
              radial-gradient(circle at 70% 60%, rgba(245,158,11,0.06) 0%, transparent 50%);
  pointer-events: none;
}
.learn-hero .hero-badge {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  background: rgba(255,255,255,0.08);
  color: var(--color-quantum-gold);
  padding: var(--space-1) var(--space-4);
  border-radius: var(--radius-full);
  font-size: var(--text-sm);
  font-weight: 500;
  margin-bottom: var(--space-6);
}
.learn-hero h1 {
  font-size: var(--text-5xl);
  font-weight: 900;
  color: var(--text-inverse);
  letter-spacing: -0.03em;
  max-width: 800px;
  margin: 0 auto var(--space-4);
}
.learn-hero .hero-sub {
  font-size: var(--text-xl);
  color: var(--color-neutron-grey);
  max-width: 600px;
  margin: 0 auto var(--space-8);
}
.learn-hero .path-buttons {
  display: flex;
  gap: var(--space-4);
  justify-content: center;
  flex-wrap: wrap;
}
.learn-hero .path-btn {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-3) var(--space-6);
  border-radius: var(--radius-full);
  font-weight: 600;
  font-size: var(--text-sm);
  transition: var(--transition-spring);
  cursor: pointer;
  border: 2px solid rgba(255,255,255,0.2);
  color: var(--text-inverse);
  background: rgba(255,255,255,0.06);
}
.learn-hero .path-btn:hover {
  background: var(--color-electric);
  border-color: var(--color-electric);
  transform: translateY(-2px);
  box-shadow: var(--shadow-glow);
}

/* ── Learning Paths ── */
.learning-paths {
  padding: var(--space-16) 0;
  background: var(--color-photon-white);
}
.learning-paths .section-header {
  text-align: center;
  margin-bottom: var(--space-12);
}
.learning-paths .section-header h2 {
  font-size: var(--text-3xl);
  font-weight: 800;
  color: var(--color-space-navy);
}
.learning-paths .section-header p {
  color: var(--color-neutron-grey);
  margin: var(--space-2) auto 0;
  max-width: 500px;
}
.path-card {
  background: var(--color-photon-white);
  border-radius: var(--radius-xl);
  padding: var(--space-8);
  border: 1px solid rgba(148,163,184,0.15);
  transition: var(--transition-base);
  position: relative;
  overflow: hidden;
}
.path-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
  border-color: var(--color-electric);
}
.path-card .path-icon {
  width: 56px;
  height: 56px;
  border-radius: var(--radius-lg);
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: var(--space-4);
}
.path-card .path-icon svg { width: 32px; height: 32px; }
.path-card .path-icon.blue { background: rgba(37,99,235,0.1); color: var(--color-electric); }
.path-card .path-icon.gold { background: rgba(245,158,11,0.1); color: var(--color-quantum-gold); }
.path-card .path-icon.purple { background: rgba(124,58,237,0.1); color: var(--color-soft-purple); }
.path-card h3 { font-size: var(--text-xl); font-weight: 700; margin-bottom: var(--space-2); }
.path-card .path-desc {
  color: var(--color-neutron-grey);
  font-size: var(--text-sm);
  font-family: var(--font-body);
  line-height: 1.6;
  margin-bottom: var(--space-4);
}
.path-card .path-meta {
  display: flex;
  gap: var(--space-4);
  margin-bottom: var(--space-4);
  font-size: var(--text-xs);
  color: var(--color-neutron-grey);
}
.path-card .path-meta span {
  display: flex;
  align-items: center;
  gap: var(--space-1);
}
.path-card .path-meta svg { width: 14px; height: 14px; }
.path-card .topic-chips {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  margin-bottom: var(--space-4);
}
.path-card .topic-chip {
  padding: var(--space-1) var(--space-3);
  background: var(--color-ice-blue);
  border-radius: var(--radius-full);
  font-size: var(--text-xs);
  font-weight: 500;
  color: var(--color-electric);
}
.path-card .path-progress {
  margin-bottom: var(--space-4);
}
.path-card .path-progress-label {
  display: flex;
  justify-content: space-between;
  font-size: var(--text-xs);
  margin-bottom: var(--space-1);
  color: var(--color-neutron-grey);
}
.path-card .progress-bar .fill.gold { background: var(--color-quantum-gold); }
.path-card .progress-bar .fill.purple { background: var(--color-soft-purple); }

/* ── Browse Topics Grid ── */
.browse-topics {
  padding: var(--space-16) 0;
  background: rgba(148,163,184,0.04);
}
.browse-topics .section-header {
  text-align: center;
  margin-bottom: var(--space-12);
}
.browse-topics .section-header h2 {
  font-size: var(--text-3xl);
  font-weight: 800;
  color: var(--color-space-navy);
}
.topic-card-learn {
  background: var(--color-photon-white);
  border-radius: var(--radius-lg);
  padding: var(--space-6);
  border: 1px solid rgba(148,163,184,0.12);
  transition: var(--transition-base);
  cursor: pointer;
  display: flex;
  align-items: flex-start;
  gap: var(--space-4);
}
.topic-card-learn:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
  border-color: var(--color-electric);
}
.topic-card-learn .topic-icon-learn {
  width: 44px;
  height: 44px;
  border-radius: var(--radius-lg);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}
.topic-card-learn .topic-icon-learn svg { width: 24px; height: 24px; }
.topic-card-learn .topic-info h4 {
  font-size: var(--text-base);
  font-weight: 600;
  margin-bottom: var(--space-1);
}
.topic-card-learn .topic-info p {
  font-size: var(--text-xs);
  color: var(--color-neutron-grey);
  font-family: var(--font-body);
  line-height: 1.5;
}
.topic-card-learn .article-count {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  font-size: var(--text-xs);
  color: var(--color-electric);
  font-weight: 500;
  margin-top: var(--space-2);
}

/* ── Recently Added Articles ── */
.recently-added {
  padding: var(--space-16) 0;
  background: var(--color-photon-white);
}
.recently-added .section-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: var(--space-8);
}
.recently-added .section-header h2 {
  font-size: var(--text-3xl);
  font-weight: 800;
  color: var(--color-space-navy);
}
.article-card {
  background: var(--color-photon-white);
  border-radius: var(--radius-lg);
  overflow: hidden;
  border: 1px solid rgba(148,163,184,0.12);
  transition: var(--transition-base);
}
.article-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
  border-color: var(--color-electric);
}
.article-card .article-card-thumb {
  aspect-ratio: 16/9;
  background: linear-gradient(135deg, var(--color-academic-blue), var(--color-slate));
  position: relative;
  overflow: hidden;
}
.article-card .article-card-thumb svg {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
}
.article-card .article-card-body {
  padding: var(--space-4);
}
.article-card .article-card-body .card-badges {
  display: flex;
  gap: var(--space-2);
  margin-bottom: var(--space-2);
}
.article-card .article-card-body h4 {
  font-size: var(--text-base);
  font-weight: 700;
  line-height: 1.35;
  margin-bottom: var(--space-2);
}
.article-card .article-card-body p {
  font-size: var(--text-sm);
  color: var(--color-neutron-grey);
  font-family: var(--font-body);
  line-height: 1.6;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}
.article-card .article-card-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-top: var(--space-3);
  border-top: 1px solid rgba(148,163,184,0.1);
  font-size: var(--text-xs);
  color: var(--color-neutron-grey);
  margin-top: var(--space-3);
}

/* ── Featured Article ── */
.featured-article {
  padding: var(--space-16) 0;
  background: linear-gradient(135deg, var(--color-academic-blue), var(--color-slate));
}
.featured-article .section-header {
  margin-bottom: var(--space-8);
}
.featured-article .section-header h2 {
  font-size: var(--text-3xl);
  font-weight: 800;
  color: var(--text-inverse);
}
.featured-card {
  display: grid;
  grid-template-columns: 1fr 1fr;
  background: rgba(255,255,255,0.05);
  border-radius: var(--radius-xl);
  overflow: hidden;
  border: 1px solid rgba(255,255,255,0.1);
}
.featured-card .featured-image {
  background: linear-gradient(-45deg, #1a1a2e, #16213e, #0f3460, #533483);
  background-size: 400% 400%;
  animation: gradientShift 15s ease infinite;
  min-height: 320px;
  display: flex;
  align-items: center;
  justify-content: center;
  position: relative;
  overflow: hidden;
}
@keyframes gradientShift {
  0% { background-position: 0% 50%; }
  50% { background-position: 100% 50%; }
  100% { background-position: 0% 50%; }
}
.featured-card .featured-image svg {
  width: 60%;
  height: 60%;
  opacity: 0.9;
}
.featured-card .featured-body {
  padding: var(--space-8);
  display: flex;
  flex-direction: column;
  justify-content: center;
}
.featured-card .featured-body .badge {
  margin-bottom: var(--space-3);
  align-self: flex-start;
}
.featured-card .featured-body h3 {
  font-size: var(--text-2xl);
  font-weight: 800;
  color: var(--text-inverse);
  line-height: 1.3;
  margin-bottom: var(--space-3);
}
.featured-card .featured-body p {
  color: rgba(255,255,255,0.7);
  font-size: var(--text-sm);
  font-family: var(--font-body);
  line-height: 1.7;
  display: -webkit-box;
  -webkit-line-clamp: 4;
  -webkit-box-orient: vertical;
  overflow: hidden;
  margin-bottom: var(--space-4);
}
.featured-card .featured-body .featured-meta {
  display: flex;
  align-items: center;
  gap: var(--space-4);
  color: rgba(255,255,255,0.5);
  font-size: var(--text-xs);
  margin-bottom: var(--space-4);
}
.featured-card .featured-body .featured-meta span {
  display: flex;
  align-items: center;
  gap: var(--space-1);
}
.featured-card .featured-body .featured-meta svg { width: 14px; height: 14px; }

/* ── Article Listing Page ── */
.articles-page {
  padding-top: 68px;
  min-height: 100vh;
}
.articles-header {
  background: var(--color-space-navy);
  padding: var(--space-16) 0 var(--space-10);
}
.articles-header h1 {
  font-size: var(--text-4xl);
  font-weight: 900;
  color: var(--text-inverse);
  letter-spacing: -0.03em;
}
.articles-header p {
  color: var(--color-neutron-grey);
  font-size: var(--text-lg);
  margin-top: var(--space-2);
}
.articles-filters {
  padding: var(--space-5) 0;
  background: var(--color-photon-white);
  border-bottom: 1px solid rgba(148,163,184,0.15);
  position: sticky;
  top: 68px;
  z-index: var(--z-sticky);
}
.articles-grid-page {
  padding: var(--space-8) 0 var(--space-16);
}
.filter-bar {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  flex-wrap: wrap;
}
.filter-bar select {
  padding: var(--space-2) var(--space-4);
  border: 1px solid rgba(148,163,184,0.3);
  border-radius: var(--radius-md);
  font-size: var(--text-sm);
  background: var(--color-photon-white);
  color: var(--color-dark-grey);
  cursor: pointer;
}
.filter-bar .filter-active {
  background: var(--color-electric);
  color: var(--text-inverse);
  border-color: var(--color-electric);
}

/* ── Article Reader ── */
.article-reader {
  padding-top: 68px;
}

/* Reading Progress Bar */
.reading-progress {
  position: fixed;
  top: 68px;
  left: 0;
  right: 0;
  height: 3px;
  background: rgba(148,163,184,0.1);
  z-index: var(--z-sticky);
}
.reading-progress .progress-fill {
  height: 100%;
  background: var(--color-electric);
  width: 0%;
  transition: width 0.1s linear;
}

/* Article Layout */
.article-layout {
  display: grid;
  grid-template-columns: 200px 1fr 240px;
  gap: var(--space-10);
  max-width: 1280px;
  margin: 0 auto;
  padding: var(--space-8) var(--space-6);
  align-items: start;
}

/* Table of Contents */
.article-toc {
  position: sticky;
  top: calc(68px + var(--space-12));
  max-height: calc(100vh - 120px);
  overflow-y: auto;
}
.article-toc h4 {
  font-size: var(--text-xs);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--color-neutron-grey);
  margin-bottom: var(--space-3);
}
.article-toc nav a {
  display: block;
  padding: var(--space-1) 0;
  font-size: var(--text-sm);
  color: var(--color-neutron-grey);
  line-height: 1.5;
  border-left: 2px solid transparent;
  padding-left: var(--space-3);
  transition: var(--transition-fast);
}
.article-toc nav a:hover { color: var(--color-electric); text-decoration: none; }
.article-toc nav a.active {
  color: var(--color-electric);
  border-left-color: var(--color-electric);
  font-weight: 600;
}
.article-toc nav a.toc-h3 { padding-left: var(--space-8); font-size: var(--text-xs); }

/* Mobile TOC toggle */
.toc-mobile-toggle {
  display: none;
  position: fixed;
  bottom: var(--space-6);
  right: var(--space-6);
  width: 48px;
  height: 48px;
  border-radius: var(--radius-full);
  background: var(--color-electric);
  color: var(--text-inverse);
  box-shadow: var(--shadow-lg);
  align-items: center;
  justify-content: center;
  z-index: var(--z-drawer);
  cursor: pointer;
  font-size: 20px;
}
.toc-mobile-panel {
  display: none;
  position: fixed;
  inset: 0;
  background: var(--color-photon-white);
  z-index: var(--z-modal);
  padding: var(--space-12) var(--space-6);
  overflow-y: auto;
  flex-direction: column;
}
.toc-mobile-panel.open { display: flex; }
.toc-mobile-panel .toc-close {
  position: absolute;
  top: var(--space-4);
  right: var(--space-4);
  font-size: 24px;
  cursor: pointer;
  width: 40px;
  height: 40px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-full);
  border: none;
  background: rgba(148,163,184,0.1);
}

/* Main Article Content */
.article-main {
  max-width: 680px;
  margin: 0 auto;
  min-width: 0;
}

/* Article Header */
.article-header {
  margin-bottom: var(--space-8);
}
.article-header .article-breadcrumb {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-sm);
  color: var(--color-neutron-grey);
  margin-bottom: var(--space-4);
  flex-wrap: wrap;
}
.article-header .article-breadcrumb a { color: var(--color-neutron-grey); }
.article-header .article-breadcrumb a:hover { color: var(--color-electric); }
.article-header .article-breadcrumb .sep { color: var(--color-neutron-grey); font-size: var(--text-xs); }
.article-header .article-tags {
  display: flex;
  gap: var(--space-2);
  flex-wrap: wrap;
  margin-bottom: var(--space-3);
}
.article-header h1 {
  font-size: var(--text-4xl);
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.2;
  color: var(--color-space-navy);
  margin-bottom: var(--space-3);
}
.article-header .article-subtitle {
  font-size: var(--text-xl);
  font-style: italic;
  color: var(--color-neutron-grey);
  font-family: var(--font-body);
  line-height: 1.6;
  margin-bottom: var(--space-5);
}
.article-header .author-card {
  display: flex;
  align-items: center;
  gap: var(--space-4);
  padding: var(--space-4);
  background: var(--color-ice-blue);
  border-radius: var(--radius-lg);
}
.article-header .author-card .author-info h5 {
  font-size: var(--text-base);
  font-weight: 600;
  color: var(--color-space-navy);
}
.article-header .author-card .author-info span {
  font-size: var(--text-xs);
  color: var(--color-neutron-grey);
}
.article-header .cover-image {
  margin-top: var(--space-6);
  aspect-ratio: 16/9;
  border-radius: var(--radius-xl);
  overflow: hidden;
  background: linear-gradient(135deg, #0f0f23, #1a1a3e, #0d1b3e);
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
}

/* Article Body */
.article-body {
  font-family: var(--font-body);
  font-size: var(--text-lg);
  line-height: 1.8;
  color: var(--color-dark-grey);
}
.article-body h2 {
  font-family: var(--font-display);
  font-size: var(--text-2xl);
  font-weight: 700;
  color: var(--color-space-navy);
  margin-top: var(--space-12);
  margin-bottom: var(--space-4);
  padding-bottom: var(--space-2);
  border-bottom: 1px solid rgba(148,163,184,0.15);
}
.article-body h3 {
  font-family: var(--font-display);
  font-size: var(--text-xl);
  font-weight: 700;
  color: var(--color-space-navy);
  margin-top: var(--space-8);
  margin-bottom: var(--space-3);
}
.article-body p {
  font-family: var(--font-body);
  line-height: 1.8;
  max-width: 68ch;
  margin-bottom: var(--space-4);
}
.article-body .equation-block {
  margin: var(--space-8) 0;
}
.article-body figure {
  margin: var(--space-8) 0;
  text-align: center;
}
.article-body figcaption {
  margin-top: var(--space-2);
  font-size: var(--text-sm);
  font-style: italic;
  color: var(--color-neutron-grey);
}

/* Callout Boxes */
.callout-box {
  padding: var(--space-5) var(--space-6);
  margin: var(--space-6) 0;
  border-radius: var(--radius-lg);
  border-left: 5px solid;
  background: var(--color-photon-white);
  box-shadow: var(--shadow-sm);
}
.callout-box .callout-title {
  font-family: var(--font-display);
  font-weight: 700;
  font-size: var(--text-sm);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: var(--space-2);
  display: flex;
  align-items: center;
  gap: var(--space-2);
}
.callout-box .callout-title svg { width: 18px; height: 18px; }
.callout-definition { border-color: var(--color-electric); background: rgba(37,99,235,0.04); }
.callout-definition .callout-title { color: var(--color-electric); }
.callout-theorem { border-color: var(--color-soft-purple); background: rgba(124,58,237,0.04); }
.callout-theorem .callout-title { color: var(--color-soft-purple); }
.callout-proof { border-color: var(--color-fusion-green); background: rgba(16,185,129,0.04); }
.callout-proof .callout-title { color: var(--color-fusion-green); }
.callout-warning { border-color: var(--color-alert-red); background: rgba(239,68,68,0.04); }
.callout-warning .callout-title { color: var(--color-alert-red); }
.callout-funfact { border-color: var(--color-quantum-gold); background: rgba(245,158,11,0.04); }
.callout-funfact .callout-title { color: var(--color-dark-gold); }

/* Key Takeaways */
.key-takeaways {
  background: linear-gradient(135deg, rgba(245,158,11,0.08), rgba(245,158,11,0.02));
  border: 1px solid rgba(245,158,11,0.15);
  border-radius: var(--radius-lg);
  padding: var(--space-6);
  margin: var(--space-8) 0;
}
.key-takeaways h4 {
  font-size: var(--text-base);
  font-weight: 700;
  color: var(--color-dark-gold);
  display: flex;
  align-items: center;
  gap: var(--space-2);
  margin-bottom: var(--space-3);
}
.key-takeaways h4 svg { width: 20px; height: 20px; }
.key-takeaways ul {
  list-style: none;
  padding: 0;
}
.key-takeaways li {
  padding: var(--space-1) 0;
  font-family: var(--font-body);
  font-size: var(--text-base);
  color: var(--color-dark-grey);
  display: flex;
  align-items: flex-start;
  gap: var(--space-2);
  line-height: 1.6;
}
.key-takeaways li::before {
  content: '→';
  color: var(--color-quantum-gold);
  font-weight: 700;
  flex-shrink: 0;
}

/* Article Sidebar */
.article-sidebar {
  position: sticky;
  top: calc(68px + var(--space-12));
  display: flex;
  flex-direction: column;
  gap: var(--space-6);
}
.sidebar-box {
  background: var(--color-photon-white);
  border: 1px solid rgba(148,163,184,0.12);
  border-radius: var(--radius-lg);
  padding: var(--space-5);
}
.sidebar-box h4 {
  font-size: var(--text-xs);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--color-neutron-grey);
  margin-bottom: var(--space-3);
}
.sidebar-box .share-buttons {
  display: flex;
  gap: var(--space-2);
}
.sidebar-box .share-btn {
  width: 36px;
  height: 36px;
  border-radius: var(--radius-full);
  display: flex;
  align-items: center;
  justify-content: center;
  border: 1px solid rgba(148,163,184,0.2);
  color: var(--color-neutron-grey);
  transition: var(--transition-fast);
  cursor: pointer;
}
.sidebar-box .share-btn:hover {
  background: var(--color-electric);
  border-color: var(--color-electric);
  color: var(--text-inverse);
}
.sidebar-box .related-articles a {
  display: block;
  padding: var(--space-2) 0;
  font-size: var(--text-sm);
  color: var(--color-dark-grey);
  line-height: 1.4;
  border-bottom: 1px solid rgba(148,163,184,0.08);
}
.sidebar-box .related-articles a:last-child { border-bottom: none; }
.sidebar-box .related-articles a:hover { color: var(--color-electric); text-decoration: none; }

/* Article Footer */
.article-footer {
  margin-top: var(--space-12);
  padding-top: var(--space-8);
  border-top: 1px solid rgba(148,163,184,0.15);
}
.article-footer .article-tags-row {
  display: flex;
  gap: var(--space-2);
  flex-wrap: wrap;
  margin-bottom: var(--space-6);
}
.article-footer .helpful-section {
  display: flex;
  align-items: center;
  gap: var(--space-4);
  margin-bottom: var(--space-6);
  padding: var(--space-4);
  background: var(--color-ice-blue);
  border-radius: var(--radius-lg);
}
.article-footer .helpful-section span {
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--color-dark-grey);
}
.article-footer .helpful-section button {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-4);
  border-radius: var(--radius-full);
  border: 1px solid rgba(148,163,184,0.3);
  background: var(--color-photon-white);
  font-size: var(--text-sm);
  font-weight: 500;
  cursor: pointer;
  transition: var(--transition-fast);
  color: var(--color-dark-grey);
}
.article-footer .helpful-section button:hover { background: var(--color-electric); color: var(--text-inverse); border-color: var(--color-electric); }
.article-footer .helpful-section button.voted { background: var(--color-electric); color: var(--text-inverse); border-color: var(--color-electric); }
.article-footer .next-articles {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-4);
  margin-bottom: var(--space-6);
}
.article-footer .next-articles .next-card {
  padding: var(--space-5);
  border: 1px solid rgba(148,163,184,0.15);
  border-radius: var(--radius-lg);
  transition: var(--transition-base);
  cursor: pointer;
}
.article-footer .next-articles .next-card:hover {
  border-color: var(--color-electric);
  box-shadow: var(--shadow-md);
  text-decoration: none;
}
.article-footer .next-articles .next-card .direction {
  font-size: var(--text-xs);
  color: var(--color-neutron-grey);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: var(--space-1);
}
.article-footer .next-articles .next-card h5 {
  font-size: var(--text-base);
  font-weight: 600;
  color: var(--color-space-navy);
  line-height: 1.3;
}
.article-footer .comments-link {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  padding: var(--space-5);
  background: var(--color-ice-blue);
  border-radius: var(--radius-lg);
  margin-bottom: var(--space-6);
  font-weight: 600;
  color: var(--color-electric);
}
.article-footer .author-bio {
  display: flex;
  gap: var(--space-5);
  padding: var(--space-6);
  background: var(--color-photon-white);
  border: 1px solid rgba(148,163,184,0.15);
  border-radius: var(--radius-xl);
  margin-top: var(--space-6);
}
.article-footer .author-bio .bio-text h5 {
  font-size: var(--text-lg);
  font-weight: 700;
  margin-bottom: var(--space-1);
}
.article-footer .author-bio .bio-text .bio-role {
  font-size: var(--text-sm);
  color: var(--color-neutron-grey);
  margin-bottom: var(--space-2);
}
.article-footer .author-bio .bio-text p {
  font-size: var(--text-sm);
  font-family: var(--font-body);
  line-height: 1.6;
  color: var(--color-dark-grey);
}

/* Code blocks in article */
.article-body .code-block {
  margin: var(--space-6) 0;
}

/* ── Mobile Responsive ── */
@media (max-width: 1023px) {
  .article-layout {
    grid-template-columns: 1fr;
  }
  .article-toc { display: none; }
  .article-sidebar { display: none; }
  .toc-mobile-toggle { display: flex; }

  .featured-card {
    grid-template-columns: 1fr;
  }
  .featured-card .featured-image { min-height: 200px; }

  .learn-hero h1 { font-size: var(--text-3xl); }
  .learn-hero .hero-sub { font-size: var(--text-base); }

  .article-header h1 { font-size: var(--text-2xl); }
  .article-header .article-subtitle { font-size: var(--text-base); }
  .article-body { font-size: var(--text-base); }
  .article-body h2 { font-size: var(--text-xl); }
  .article-footer .next-articles { grid-template-columns: 1fr; }
}

@media (max-width: 639px) {
  .learn-hero h1 { font-size: var(--text-2xl); }
  .learn-hero .path-buttons { flex-direction: column; align-items: center; }

  .path-card { padding: var(--space-5); }

  .article-header h1 { font-size: var(--text-xl); }
  .article-header .author-card { flex-wrap: wrap; }
  .article-footer .author-bio { flex-direction: column; }

  .articles-filters { position: static; }
  .filter-bar { flex-direction: column; align-items: stretch; }
}

/* ═══════════════════════════════════════════════════════════════════════════
   v5.0 — LEARN IS NOT THE FORUM

   Learn articles are curated reference material, so the chrome is different
   by design: a curriculum trail instead of category chips, no author block,
   no thread-style timestamps, and sequential navigation so a lesson leads
   somewhere instead of dead-ending.
   ═══════════════════════════════════════════════════════════════════════════ */

/* ── Curriculum trail: Mechanics › Rotational Dynamics › Moment of Inertia ── */
.learn-trail {
  display: flex; flex-wrap: wrap; align-items: center; gap: 6px;
  font-size: 13px; margin-bottom: 12px;
}
.learn-trail-link {
  color: var(--text-muted);
  text-decoration: none;
  padding: 2px 8px;
  border-radius: 999px;
  transition: background-color .15s ease, color .15s ease;
}
.learn-trail-link:hover { background: var(--surface-sunken); color: var(--border-focus); }
.learn-trail-link:last-child { color: var(--text); font-weight: 600; }
.learn-trail-sep { color: var(--text-faint); font-size: 12px; }

/* ── Meta strip: only what a learner needs ── */
.learn-meta {
  display: flex; flex-wrap: wrap; gap: 16px;
  font-size: 13px; color: var(--text-muted);
  padding-bottom: 14px; border-bottom: 1px solid var(--border);
}
.learn-meta-updated { font-style: italic; color: var(--text-faint); }

/* ── Sequential lesson navigation ── */
.learn-pager {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: stretch;
  gap: 12px;
  max-width: 820px;
  margin: 40px auto 0;
  padding: 20px 0 0;
  border-top: 1px solid var(--border);
}
.learn-pager-link {
  display: flex; flex-direction: column; gap: 4px;
  padding: 14px 16px;
  border: 1px solid var(--border);
  border-radius: 12px;
  background: var(--surface);
  text-decoration: none;
  transition: border-color .15s ease, box-shadow .15s ease, transform .15s ease;
}
.learn-pager-link:hover {
  border-color: var(--border-focus);
  box-shadow: var(--shadow-sm);
  transform: translateY(-1px);
}
.learn-pager-next { text-align: right; }
.learn-pager-dir { font-size: 12px; font-weight: 600; color: var(--text-muted); }
.learn-pager-title { font-size: 14px; font-weight: 600; color: var(--text); line-height: 1.35; }
.learn-pager-count {
  align-self: center;
  font-size: 12px; color: var(--text-faint); white-space: nowrap;
}

@media (max-width: 640px) {
  .learn-pager { grid-template-columns: 1fr; }
  .learn-pager-next { text-align: left; }
  .learn-pager-count { order: -1; text-align: center; }
}

@media (prefers-reduced-motion: reduce) {
  .learn-pager-link:hover { transform: none; }
}

/* ── Subject grid on the Learn hub (v5.0) ─────────────────────────────── */
.learn-subject-grid { margin-top: var(--space-6); }
.learn-subject-card {
  border: 1px solid var(--border);
  border-radius: 12px;
  background: var(--surface);
  padding: 18px 20px;
  transition: border-color .15s ease, box-shadow .15s ease;
}
.learn-subject-card:hover { border-color: var(--border-focus); box-shadow: var(--shadow-sm); }
.learn-subject-head { display: block; text-decoration: none; }
.learn-subject-head h4 {
  margin: 0 0 4px; font-size: 16px; font-weight: 700; color: var(--text);
}
.learn-subject-head .article-count { font-size: 12px; color: var(--text-muted); }
.learn-subject-children {
  list-style: none; margin: 12px 0 0; padding: 12px 0 0;
  border-top: 1px solid var(--border);
  display: flex; flex-direction: column; gap: 6px;
}
.learn-subject-children a {
  font-size: 13px; color: var(--text-secondary); text-decoration: none;
}
.learn-subject-children a:hover { color: var(--border-focus); }

/* ── Subject archive ──────────────────────────────────────────────────── */
.learn-archive-head { margin: 18px 0 28px; }
.learn-archive-head h1 { font-size: 30px; font-weight: 800; margin: 0 0 6px; color: var(--text); }
.learn-archive-desc { color: var(--text-muted); font-size: 15px; margin: 0; max-width: 60ch; }

.learn-section-label {
  font-size: 12px; font-weight: 700; text-transform: uppercase;
  letter-spacing: .05em; color: var(--text-muted);
  margin: 0 0 14px;
}
.learn-subtopics { margin-bottom: 36px; }
.learn-subtopic-card {
  display: block; padding: 14px 16px;
  border: 1px solid var(--border); border-radius: 10px;
  background: var(--surface); text-decoration: none;
  transition: border-color .15s ease;
}
.learn-subtopic-card:hover { border-color: var(--border-focus); }
.learn-subtopic-card h4 { margin: 0 0 3px; font-size: 14px; font-weight: 600; color: var(--text); }
.learn-subtopic-card .article-count { font-size: 12px; color: var(--text-muted); }

/* ── Numbered lesson list — reads as a syllabus, not a feed ───────────── */
.learn-lesson-list { list-style: none; margin: 0; padding: 0; counter-reset: lesson; }
.learn-lesson-row {
  display: flex; align-items: flex-start; gap: 14px;
  padding: 16px 0; border-bottom: 1px solid var(--border);
}
.learn-lesson-row:last-child { border-bottom: 0; }
.learn-lesson-num {
  flex: 0 0 28px; height: 28px; border-radius: 50%;
  background: var(--surface-sunken); color: var(--text-muted);
  display: flex; align-items: center; justify-content: center;
  font-size: 12px; font-weight: 700;
}
.learn-lesson-body { flex: 1 1 auto; min-width: 0; }
.learn-lesson-title {
  display: block; font-size: 15px; font-weight: 600;
  color: var(--text); text-decoration: none; line-height: 1.35;
}
.learn-lesson-title:hover { color: var(--border-focus); }
.learn-lesson-excerpt {
  margin: 4px 0 0; font-size: 13px; color: var(--text-muted); line-height: 1.5;
}
.learn-lesson-time {
  flex: 0 0 auto; font-size: 12px; color: var(--text-faint); white-space: nowrap; padding-top: 4px;
}

/* ── Empty states — guide the admin instead of showing a blank page ───── */
.learn-empty {
  text-align: center; padding: 40px 20px;
  border: 1px dashed var(--border); border-radius: 12px;
  color: var(--text-muted);
}
.learn-empty-hint { font-size: 12px; color: var(--text-faint); margin-top: 8px; }

@media (max-width: 640px) {
  .learn-lesson-excerpt { display: none; }
}