/* Lesson page — same light theme, full width, sharp */

/* ---- Layout: sidebar + main (W3Schools-style) ---- */
.learn-page-wrapper {
  display: flex;
  position: relative;
  min-height: calc(100vh - var(--header-h) - 120px);
  background: var(--bg-page);
}

/* Sidebar: fixed left on desktop */
.learn-sidebar {
  --learn-sidebar-width: 280px;
  flex: 0 0 var(--learn-sidebar-width);
  width: var(--learn-sidebar-width);
  position: sticky;
  top: var(--header-h);
  align-self: flex-start;
  max-height: calc(100vh - var(--header-h));
  overflow-y: auto;
  overflow-x: hidden;
  background: var(--bg-elevated);
  border-right: 1px solid var(--border);
  z-index: 10;
  transition: transform 0.25s ease, visibility 0.25s ease;
  /* Scrollbar: thin and styled (Firefox) */
  scrollbar-width: thin;
  scrollbar-gutter: stable;
  scrollbar-color: var(--charcoal-light) transparent;
}

/* Scrollbar styling (WebKit: Chrome, Edge, Safari) */
.learn-sidebar::-webkit-scrollbar {
  width: 8px;
}

.learn-sidebar::-webkit-scrollbar-track {
  background: transparent;
  margin: var(--space-xs) 0;
}

.learn-sidebar::-webkit-scrollbar-thumb {
  background: var(--charcoal-light);
  border-radius: 4px;
  min-height: 48px;
}

.learn-sidebar::-webkit-scrollbar-thumb:hover {
  background: var(--charcoal-muted);
}

.learn-sidebar::-webkit-scrollbar-thumb:active {
  background: var(--charcoal-soft);
}

.learn-sidebar::-webkit-scrollbar-corner {
  background: transparent;
}

.learn-sidebar-inner {
  padding: var(--space-lg) 0;
}

.learn-sidebar-all {
  display: block;
  padding: var(--space-sm) var(--space-xl);
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--text-secondary);
}

.learn-sidebar-all:hover {
  color: var(--text-primary);
}

.learn-sidebar-nav {
  margin-top: var(--space-sm);
}

.learn-sidebar-section {
  border: none;
  margin: 0;
}

.learn-sidebar-section-title {
  display: block;
  padding: var(--space-sm) var(--space-xl);
  font-family: var(--font-sans);
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--text-primary);
  text-transform: uppercase;
  letter-spacing: 0.04em;
  cursor: pointer;
  list-style: none;
  background: var(--chapter-accent);
  border-top: 1px solid var(--border);
  user-select: none;
}

.learn-sidebar-section-title::-webkit-details-marker {
  display: none;
}

.learn-sidebar-section-title::before {
  content: "▾ ";
  font-size: 0.7rem;
  opacity: 0.7;
}

.learn-sidebar-section:not([open]) .learn-sidebar-section-title::before {
  content: "▸ ";
}

.learn-sidebar-list {
  margin: 0;
  padding: var(--space-xs) 0 var(--space-sm);
  list-style: none;
  border-top: 1px solid var(--border);
}

.learn-sidebar-list li {
  margin: 0;
}

.learn-sidebar-link {
  display: block;
  padding: var(--space-xs) var(--space-xl);
  font-size: 0.85rem;
  color: var(--text-secondary);
  line-height: 1.4;
}

.learn-sidebar-link:hover {
  color: var(--text-primary);
  background: var(--almond);
}

.learn-sidebar-link.is-active {
  font-weight: 600;
  color: var(--accent);
  background: var(--chapter-accent);
  border-left: 3px solid var(--accent);
}

/* Main content area */
.learn-page {
  flex: 1;
  min-width: 0;
  padding: var(--space-2xl) 0 var(--space-3xl);
  background: var(--bg-page);
}

.learn-article {
  width: 100%;
  max-width: 100%;
}

/* Mobile: toggle button (before content) */
.learn-sidebar-toggle {
  display: none;
  position: fixed;
  bottom: var(--space-xl);
  left: var(--space-xl);
  z-index: 100;
  padding: var(--space-md) var(--space-lg);
  font-family: var(--font-sans);
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--cta-text);
  background: var(--cta-bg);
  border: 1px solid var(--charcoal);
  cursor: pointer;
  box-shadow: 0 4px 12px rgba(54, 69, 79, 0.2);
  align-items: center;
  gap: var(--space-sm);
}

.learn-sidebar-toggle:hover {
  background: var(--cta-hover-bg);
  color: var(--cta-hover-text);
}

.learn-sidebar-toggle-icon {
  font-size: 1.25rem;
  line-height: 1;
}

.learn-sidebar-overlay {
  display: none;
  position: fixed;
  inset: 0;
  top: var(--header-h);
  background: rgba(54, 69, 79, 0.4);
  z-index: 8;
  opacity: 0;
  transition: opacity 0.25s ease;
  pointer-events: none;
}

.learn-page-wrapper.learn-sidebar-open .learn-sidebar-overlay {
  pointer-events: auto;
  opacity: 1;
}

@media (max-width: 991px) {
  .learn-sidebar-toggle {
    display: flex;
  }

  .learn-sidebar {
    position: fixed;
    top: var(--header-h);
    left: 0;
    bottom: 0;
    width: min(85vw, var(--learn-sidebar-width));
    max-height: none;
    transform: translateX(-100%);
    visibility: hidden;
    box-shadow: 4px 0 16px rgba(54, 69, 79, 0.1);
  }

  .learn-page-wrapper.learn-sidebar-open .learn-sidebar {
    transform: translateX(0);
    visibility: visible;
  }

  .learn-page-wrapper.learn-sidebar-open .learn-sidebar-overlay {
    display: block;
  }

  .learn-page-wrapper.learn-sidebar-open .learn-sidebar-toggle {
    left: calc(min(85vw, var(--learn-sidebar-width)) + var(--space-md));
  }
}

.learn-back {
  display: inline-block;
  font-size: 0.9rem;
  color: var(--text-secondary);
  margin-bottom: var(--space-lg);
  font-weight: 500;
}

.learn-back:hover {
  color: var(--text-primary);
}

.learn-meta {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin: 0 0 var(--space-sm);
  text-transform: uppercase;
  letter-spacing: 0.06em;
}

.learn-title {
  font-family: var(--font-sans);
  font-size: 1.75rem;
  font-weight: 600;
  margin: 0 0 var(--space-md);
  color: var(--text-primary);
  letter-spacing: -0.02em;
  line-height: 1.3;
}

.learn-lead {
  font-size: 1.05rem;
  color: var(--text-secondary);
  line-height: 1.65;
  margin: 0 0 var(--space-xl);
}

/* YouTube embed — responsive 16:9 */
.learn-video-wrap {
  margin: 0 0 var(--space-2xl);
}

.learn-video-inner {
  position: relative;
  width: 100%;
  padding-bottom: 56.25%; /* 16:9 */
  height: 0;
  overflow: hidden;
  background: var(--bg-elevated);
  border: 1px solid var(--border);
}

.learn-video-inner iframe {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}

.learn-content {
  color: var(--text-secondary);
}

.learn-content p {
  margin: 0 0 var(--space-lg);
}

.learn-content h2 {
  font-family: var(--font-sans);
  font-size: 1.2rem;
  font-weight: 600;
  margin: var(--space-xl) 0 var(--space-md);
  color: var(--text-primary);
}

.learn-content h2:first-child {
  margin-top: 0;
}

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

.learn-content a:hover {
  color: var(--charcoal);
}

.learn-content code {
  font-family: var(--font-sans);
  font-size: 0.9em;
  font-weight: 500;
  padding: 0.15em 0.4em;
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  color: var(--text-primary);
}

.learn-nav {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-md);
  margin-top: var(--space-2xl);
  padding-top: var(--space-xl);
  border-top: 1px solid var(--border);
}

.learn-nav-btn {
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--accent);
  text-decoration: none;
}

.learn-nav-btn:hover {
  color: var(--charcoal);
  text-decoration: underline;
}

.learn-nav span.learn-nav-btn,
.learn-nav-btn[aria-disabled="true"] {
  color: var(--text-muted);
  cursor: default;
  pointer-events: none;
}

.learn-nav span.learn-nav-btn:hover,
.learn-nav-btn[aria-disabled="true"]:hover {
  text-decoration: none;
}

/* Summary block — before main content */
.learn-summary {
  margin: 0 0 var(--space-2xl);
  padding: var(--space-xl);
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  border-left: 4px solid var(--accent);
}

.learn-summary h2 {
  font-family: var(--font-sans);
  font-size: 1.1rem;
  font-weight: 600;
  margin: 0 0 var(--space-md);
  color: var(--text-primary);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.learn-summary ul {
  margin: 0;
  padding-left: 1.25rem;
  color: var(--text-secondary);
  line-height: 1.6;
}

.learn-summary li {
  margin-bottom: var(--space-sm);
}

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

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

.learn-summary a:hover {
  color: var(--charcoal);
}

/* FAQ section — after main content */
.learn-faq {
  margin-top: var(--space-2xl);
  padding-top: var(--space-2xl);
  border-top: 1px solid var(--border);
}

.learn-faq h2 {
  font-family: var(--font-sans);
  font-size: 1.25rem;
  font-weight: 600;
  margin: 0 0 var(--space-lg);
  color: var(--text-primary);
}

.faq-item {
  margin-bottom: var(--space-xl);
}

.faq-item:last-child {
  margin-bottom: 0;
}

.faq-item h3 {
  font-family: var(--font-sans);
  font-size: 1rem;
  font-weight: 600;
  margin: 0 0 var(--space-sm);
  color: var(--text-primary);
}

.faq-item p {
  margin: 0;
  color: var(--text-secondary);
  line-height: 1.65;
}

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

.faq-item a:hover {
  color: var(--charcoal);
}