.lesson-layout {
  display: grid;
  grid-template-columns: 260px 1fr;
  min-height: calc(100vh - 64px);
  gap: 0;
}

/* Sidebar */
.lesson-sidebar {
  background: var(--color-bg-2);
  border-right: 1px solid var(--color-border);
  position: sticky;
  top: 64px;
  height: calc(100vh - 64px);
  overflow-y: auto;
  display: flex;
  flex-direction: column;
}

.lesson-sidebar-header {
  padding: 1.25rem 1rem;
  border-bottom: 1px solid var(--color-border);
  flex-shrink: 0;
}

.lesson-sidebar-course-link {
  display: flex;
  align-items: center;
  gap: 0.375rem;
  font-size: 0.75rem;
  color: var(--color-primary);
  text-decoration: none;
  margin-bottom: 0.5rem;
}

.lesson-sidebar-course-title {
  font-size: 0.875rem;
  font-weight: 700;
  color: var(--color-text);
  line-height: 1.3;
}

.lesson-sidebar-nav {
  flex: 1;
  padding: 0.75rem 0;
  overflow-y: auto;
}

.lesson-sidebar-module {
  margin-bottom: 0.5rem;
}

.lesson-sidebar-module-title {
  padding: 0.5rem 1rem;
  font-size: 0.7rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  color: var(--color-text-3);
}

.lesson-sidebar-lesson {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.5rem 1rem 0.5rem 1.25rem;
  font-size: 0.82rem;
  color: var(--color-text-2);
  text-decoration: none;
  border-radius: 0;
  transition: all var(--transition);
  border-left: 2px solid transparent;
}

.lesson-sidebar-lesson:hover {
  color: var(--color-text);
  background: var(--color-surface);
}

.lesson-sidebar-lesson.active {
  color: var(--color-primary);
  background: rgba(0,212,255,0.05);
  border-left-color: var(--color-primary);
}

.lesson-sidebar-lesson-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  border: 1px solid var(--color-border-2);
  flex-shrink: 0;
}

.lesson-sidebar-lesson.active .lesson-sidebar-lesson-dot {
  background: var(--color-primary);
  border-color: var(--color-primary);
}

/* Main content */
.lesson-main {
  min-width: 0;
  padding: 2.5rem 3rem;
  max-width: 820px;
}

.lesson-breadcrumb {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.78rem;
  color: var(--color-text-3);
  margin-bottom: 1.5rem;
  flex-wrap: wrap;
}

.lesson-breadcrumb a {
  color: var(--color-text-3);
  text-decoration: none;
  transition: color var(--transition);
}

.lesson-breadcrumb a:hover {
  color: var(--color-primary);
}

.lesson-header {
  margin-bottom: 2rem;
  padding-bottom: 1.5rem;
  border-bottom: 1px solid var(--color-border);
}

.lesson-module-label {
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--color-primary);
  margin-bottom: 0.625rem;
  display: block;
}

.lesson-title {
  font-size: clamp(1.5rem, 3vw, 2.25rem);
  font-weight: 900;
  letter-spacing: -0.02em;
  margin-bottom: 0.875rem;
}

.lesson-meta {
  display: flex;
  align-items: center;
  gap: 1rem;
  flex-wrap: wrap;
}

.lesson-meta-item {
  display: flex;
  align-items: center;
  gap: 0.375rem;
  font-size: 0.8rem;
  color: var(--color-text-3);
}

/* Content styles */
.lesson-content {
  line-height: 1.75;
}

.lesson-content h2 {
  font-size: 1.4rem;
  font-weight: 800;
  margin: 2.5rem 0 1rem;
  padding-top: 0.5rem;
  color: var(--color-text);
  letter-spacing: -0.01em;
}

.lesson-content h3 {
  font-size: 1.1rem;
  font-weight: 700;
  margin: 2rem 0 0.75rem;
  color: var(--color-text);
}

.lesson-content p {
  color: var(--color-text-2);
  margin-bottom: 1.25rem;
}

.lesson-content ul, .lesson-content ol {
  color: var(--color-text-2);
  margin-bottom: 1.25rem;
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
}

.lesson-content a {
  color: var(--color-primary);
  text-decoration: underline;
  text-decoration-thickness: 1px;
  text-underline-offset: 2px;
}

.lesson-content .callout {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-left: 3px solid var(--color-primary);
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  padding: 1rem 1.25rem;
  margin: 1.5rem 0;
}

.lesson-content .callout.warning {
  border-left-color: var(--color-warning);
}

.lesson-content .callout.danger {
  border-left-color: var(--color-danger);
}

.lesson-content .callout.success {
  border-left-color: var(--color-accent);
}

.lesson-content .callout-title {
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin-bottom: 0.4rem;
  color: var(--color-primary);
}

.lesson-content .callout.warning .callout-title {
  color: var(--color-warning);
}
.lesson-content .callout.danger .callout-title {
  color: var(--color-danger);
}
.lesson-content .callout.success .callout-title {
  color: var(--color-accent);
}

/* Lesson nav */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 3rem;
  padding-top: 2rem;
  border-top: 1px solid var(--color-border);
}

.lesson-nav-btn {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.75rem 1.25rem;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  text-decoration: none;
  transition: all var(--transition);
  flex: 1;
  max-width: 280px;
}

.lesson-nav-btn:hover {
  border-color: var(--color-border-2);
  background: var(--color-surface-2);
}

.lesson-nav-btn.next {
  margin-left: auto;
  text-align: right;
  flex-direction: row-reverse;
}

.lesson-nav-label {
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--color-text-3);
  display: block;
  margin-bottom: 0.2rem;
}

.lesson-nav-title {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--color-text);
  display: block;
  line-height: 1.3;
}

@media (max-width: 900px) {
  .lesson-layout {
    grid-template-columns: 1fr;
  }
  .lesson-sidebar {
    display: none;
  }
  .lesson-main {
    padding: 1.5rem 1rem;
  }
}