/* ──────────────────────────────────────────────────────────────────────────
   Lesson screen — 3-column research §2.1
   modules · main (70%) · side tabs (30%)
   ────────────────────────────────────────────────────────────────────────── */

.lesson-shell {
  display: grid;
  grid-template-columns: 280px minmax(0, 1fr) 360px;
  min-height: 100vh;
  background: var(--c-surface-2);
}

/* ─── LEFT: modules ─── */
.lesson-modules {
  background: var(--c-surface);
  border-right: 1px solid var(--c-border);
  padding: var(--s-5) 0 var(--s-6);
  position: sticky;
  top: 0;
  height: 100vh;
  overflow-y: auto;
  display: flex;
  flex-direction: column;
}
.lesson-modules-back {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 0 var(--s-5);
  font-size: var(--fs-xs);
  color: var(--c-text-muted);
  text-decoration: none;
  margin-bottom: var(--s-3);
}
.lesson-modules-back:hover { color: var(--c-primary-text); text-decoration: none; }
.lesson-modules-course {
  padding: 0 var(--s-5);
  font-size: var(--fs-md);
  font-weight: var(--fw-semibold);
  color: var(--c-text);
  line-height: var(--lh-tight);
  margin-bottom: var(--s-3);
}
.lesson-modules-progress-text {
  padding: 0 var(--s-5);
  font-size: var(--fs-xs);
  color: var(--c-text-muted);
  margin-bottom: 6px;
}
.lesson-modules-progress {
  margin: 0 var(--s-5) var(--s-4);
  height: 4px;
  background: var(--c-surface-2);
  border-radius: 999px;
  overflow: hidden;
}
.lesson-modules-progress-bar {
  height: 100%;
  background: linear-gradient(90deg, #10b981, #047857);
  border-radius: 999px;
  transition: width var(--t-normal) var(--e-out);
}
.lesson-modules-nav { flex: 1; }
.lesson-modules-section-title {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: var(--s-3) var(--s-5) 6px;
  font-size: var(--fs-xs);
  font-weight: var(--fw-semibold);
  color: var(--c-text);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}
.lesson-modules-section-idx {
  width: 20px; height: 20px;
  border-radius: 50%;
  background: var(--c-surface-2);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-size: 11px;
  color: var(--c-text-muted);
}
.lesson-modules-item {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 7px var(--s-5);
  text-decoration: none;
  color: var(--c-text);
  font-size: var(--fs-sm);
  line-height: var(--lh-tight);
  border-left: 3px solid transparent;
  transition: background var(--t-fast), color var(--t-fast), border-color var(--t-fast);
}
.lesson-modules-item:hover { background: var(--c-surface-2); text-decoration: none; }
.lesson-modules-item.is-active {
  background: var(--c-primary-soft);
  color: var(--c-primary-text);
  border-left-color: var(--c-primary);
  font-weight: var(--fw-semibold);
}
.lesson-modules-item.is-done {
  color: var(--c-text-muted);
}
.lesson-modules-item.is-done .lesson-modules-text {
  text-decoration: line-through;
  text-decoration-thickness: 1px;
  text-decoration-color: var(--c-border-strong);
}
.lesson-modules-mark {
  flex-shrink: 0;
  width: 18px; height: 18px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--c-text-light);
}
.lesson-modules-item.is-done .lesson-modules-mark { color: #10b981; }
.lesson-modules-item.is-active .lesson-modules-mark { color: var(--c-primary); }
.lesson-modules-text {
  flex: 1;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}
.lesson-modules-dur {
  flex-shrink: 0;
  font-size: 11px;
  color: var(--c-text-light);
}
.lesson-modules-test {
  margin: var(--s-4) var(--s-5) 0;
  padding-top: var(--s-4);
  border-top: 1px solid var(--c-border);
}
.lesson-modules-test-label {
  font-size: var(--fs-xs);
  color: var(--c-text-muted);
  margin-bottom: 6px;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

/* ─── CENTER: main (70%) ─── */
.lesson-main {
  padding: var(--s-6) var(--s-8) var(--s-10);
  max-width: 920px;
  margin: 0 auto;
  width: 100%;
  background: transparent;
}

.lesson-breadcrumbs {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: var(--fs-xs);
  color: var(--c-text-muted);
  margin-bottom: var(--s-3);
}
.lesson-breadcrumbs a { color: inherit; text-decoration: none; }
.lesson-breadcrumbs a:hover { color: var(--c-primary-text); text-decoration: underline; }
.lesson-breadcrumbs-sep { color: var(--c-border-strong); }
.lesson-breadcrumbs-current { color: var(--c-text); }

.lesson-title {
  font-size: var(--fs-2xl);
  font-weight: var(--fw-bold);
  line-height: var(--lh-tight);
  margin-bottom: var(--s-3);
  color: var(--c-text);
}
.lesson-meta {
  display: flex;
  gap: var(--s-5);
  align-items: center;
  flex-wrap: wrap;
  font-size: var(--fs-sm);
  color: var(--c-text-muted);
  margin-bottom: var(--s-6);
}
.lesson-meta .badge { font-size: var(--fs-xs); }

.lesson-video {
  margin-bottom: var(--s-6);
  border-radius: var(--r-lg);
  overflow: hidden;
  background: #000;
  box-shadow: var(--sh-md);
}
.lesson-video video { width: 100%; display: block; aspect-ratio: 16 / 9; }

.lesson-content {
  font-size: var(--fs-md);
  line-height: var(--lh-loose);
  color: var(--c-text);
}
.lesson-content h2, .lesson-content h3 { margin-top: var(--s-6); margin-bottom: var(--s-3); }
.lesson-content p { margin-bottom: var(--s-4); }
.lesson-content ul, .lesson-content ol { padding-left: var(--s-5); margin-bottom: var(--s-4); }
.lesson-content li { margin-bottom: 6px; }
.lesson-content code { background: var(--c-surface-2); padding: 1px 5px; border-radius: 3px; font-size: 0.9em; }
.lesson-content blockquote { border-left: 3px solid var(--c-primary); padding-left: var(--s-4); margin: var(--s-5) 0; color: var(--c-text-muted); }

/* Footer nav */
.lesson-footer-nav {
  margin-top: var(--s-8);
  padding: var(--s-5);
  background: var(--c-surface);
  border: 1px solid var(--c-border);
  border-radius: var(--r-lg);
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: var(--s-3);
  align-items: center;
}
.lesson-footer-prev { justify-self: start; min-width: 0; }
.lesson-footer-mark { justify-self: center; }
.lesson-footer-next { justify-self: end; min-width: 0; }
.lesson-footer-arrow-label {
  display: inline-block;
  max-width: 220px;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  vertical-align: bottom;
}

/* ─── RIGHT: tabs sidebar (30%) ─── */
.lesson-side {
  background: var(--c-surface);
  border-left: 1px solid var(--c-border);
  position: sticky;
  top: 0;
  height: 100vh;
  display: flex;
  flex-direction: column;
}
.lesson-side-tabs {
  display: flex;
  border-bottom: 1px solid var(--c-border);
  background: var(--c-surface);
  flex-shrink: 0;
}
.lesson-side-tab {
  flex: 1;
  background: none;
  border: none;
  border-bottom: 2px solid transparent;
  padding: var(--s-4) var(--s-2);
  font-size: var(--fs-sm);
  font-weight: var(--fw-medium);
  color: var(--c-text-muted);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  transition: color var(--t-fast), border-color var(--t-fast);
}
.lesson-side-tab:hover { color: var(--c-text); }
.lesson-side-tab.is-active {
  color: var(--c-primary-text);
  border-bottom-color: var(--c-primary);
}
.lesson-side-pane {
  display: none;
  flex: 1;
  flex-direction: column;
  overflow: hidden;
  padding: var(--s-4);
}
.lesson-side-pane.is-active { display: flex; }

/* Notes pane */
.lesson-notes-form {
  flex-shrink: 0;
  padding-bottom: var(--s-3);
  border-bottom: 1px solid var(--c-border);
  margin-bottom: var(--s-3);
}
.lesson-notes-form textarea {
  width: 100%;
  border: 1px solid var(--c-border);
  border-radius: var(--r);
  padding: 10px 12px;
  font-family: inherit;
  font-size: var(--fs-sm);
  resize: vertical;
  margin-bottom: var(--s-2);
}
.lesson-notes-form textarea:focus {
  outline: none;
  border-color: var(--c-primary);
  box-shadow: 0 0 0 3px var(--c-primary-soft);
}
.lesson-notes-form-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--s-2);
  flex-wrap: wrap;
}
.lesson-notes-tc {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: var(--fs-xs);
  color: var(--c-text-muted);
}
.lesson-notes-tc input { margin: 0; }
.lesson-notes-tc #note-tc-display {
  font-family: monospace;
  background: var(--c-surface-2);
  padding: 1px 6px;
  border-radius: 3px;
  color: var(--c-text);
}
.lesson-notes-empty-hint {
  font-size: var(--fs-xs);
  color: var(--c-text-light);
  margin-top: var(--s-2);
  line-height: var(--lh-normal);
}
.lesson-notes-list {
  overflow-y: auto;
  flex: 1;
  display: flex;
  flex-direction: column;
  gap: var(--s-2);
}
.lesson-note {
  background: var(--c-surface-2);
  border-radius: var(--r);
  padding: var(--s-3);
  font-size: var(--fs-sm);
  line-height: var(--lh-normal);
}
.lesson-note-head {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 4px;
}
.lesson-note-time {
  font-size: 11px;
  color: var(--c-text-muted);
}
.lesson-note-tc {
  color: var(--c-primary-text);
  font-family: monospace;
  text-decoration: none;
}
.lesson-note-tc:hover { text-decoration: underline; }
.lesson-note-del {
  background: none;
  border: none;
  font-size: 18px;
  line-height: 1;
  color: var(--c-text-light);
  cursor: pointer;
  padding: 0 4px;
  border-radius: 3px;
}
.lesson-note-del:hover { color: var(--c-danger); background: rgba(239, 68, 68, 0.08); }
.lesson-note-body { color: var(--c-text); white-space: pre-wrap; word-break: break-word; }

/* Transcript pane */
.lesson-side-search-row {
  padding-bottom: var(--s-3);
  flex-shrink: 0;
}
#transcript-search {
  width: 100%;
  border: 1px solid var(--c-border);
  border-radius: var(--r);
  padding: 8px 12px;
  font-family: inherit;
  font-size: var(--fs-sm);
}
#transcript-search:focus {
  outline: none;
  border-color: var(--c-primary);
  box-shadow: 0 0 0 3px var(--c-primary-soft);
}
.lesson-transcript {
  overflow-y: auto;
  flex: 1;
  font-size: var(--fs-sm);
  line-height: var(--lh-loose);
  color: var(--c-text);
}
.lesson-transcript mark {
  background: #fef08a;
  padding: 0 2px;
  border-radius: 2px;
}

/* AI pane */
.lesson-ai-intro {
  font-size: var(--fs-xs);
  color: var(--c-text-muted);
  line-height: var(--lh-normal);
  padding: var(--s-3);
  background: var(--c-primary-soft);
  border-radius: var(--r);
  margin-bottom: var(--s-3);
  flex-shrink: 0;
}
.lesson-ai-intro strong { color: var(--c-primary-text); }
.lesson-ai-messages {
  flex: 1;
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  gap: var(--s-2);
  padding-bottom: var(--s-3);
}
.lesson-ai-form {
  border-top: 1px solid var(--c-border);
  padding-top: var(--s-3);
  flex-shrink: 0;
}
.lesson-ai-form textarea {
  width: 100%;
  border: 1px solid var(--c-border);
  border-radius: var(--r);
  padding: 8px 12px;
  font-family: inherit;
  font-size: var(--fs-sm);
  margin-bottom: 6px;
  resize: vertical;
}
.lesson-ai-form textarea:focus {
  outline: none;
  border-color: var(--c-primary);
  box-shadow: 0 0 0 3px var(--c-primary-soft);
}

/* Responsive */
@media (max-width: 1280px) {
  .lesson-shell { grid-template-columns: 260px minmax(0, 1fr) 320px; }
  .lesson-main { padding: var(--s-6) var(--s-5) var(--s-10); }
}
@media (max-width: 1100px) {
  .lesson-shell { grid-template-columns: 260px minmax(0, 1fr); }
  .lesson-side {
    position: fixed;
    right: -380px;
    top: 0; bottom: 0;
    width: 360px;
    z-index: 90;
    box-shadow: -8px 0 24px rgba(0,0,0,0.1);
    transition: right var(--t-base);
  }
  .lesson-side.is-open { right: 0; }
}
@media (max-width: 768px) {
  .lesson-shell { grid-template-columns: 1fr; }
  .lesson-modules { display: none; }
  .lesson-main { padding: var(--s-4); }
  .lesson-footer-nav { grid-template-columns: 1fr; gap: var(--s-3); }
  .lesson-footer-prev, .lesson-footer-mark, .lesson-footer-next { justify-self: stretch; }
  .lesson-footer-arrow-label { max-width: 100%; }
}