/* ============================================================
   ShaderStudy – Learn Page Styles
   ============================================================ */

/* ── Layout Shell ──────────────────────────────────────────── */
.learn-shell {
  display: flex;
  height: 100vh;
  overflow: hidden;
}

/* ── Sidebar ───────────────────────────────────────────────── */
.sidebar {
  width: 280px;
  min-width: 280px;
  height: 100vh;
  display: flex;
  flex-direction: column;
  background: var(--bg-surface);
  border-right: 1px solid var(--border-subtle);
  overflow: hidden;
  transition: width var(--transition-normal), min-width var(--transition-normal);
  z-index: 50;
}

.sidebar.collapsed {
  width: 0;
  min-width: 0;
}

.sidebar-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-4) var(--space-5);
  border-bottom: 1px solid var(--border-subtle);
  flex-shrink: 0;
}

.sidebar-logo {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-base);
  font-weight: 700;
  color: var(--text-primary);
  text-decoration: none;
}

.sidebar-logo-icon {
  width: 28px;
  height: 28px;
  background: var(--gradient-accent);
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 14px;
  flex-shrink: 0;
}

.sidebar-toggle {
  width: 28px;
  height: 28px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-sm);
  color: var(--text-muted);
  transition: all var(--transition-fast);
}
.sidebar-toggle:hover { background: var(--bg-elevated); color: var(--text-primary); }

.sidebar-progress {
  padding: var(--space-4) var(--space-5);
  border-bottom: 1px solid var(--border-subtle);
  flex-shrink: 0;
}

.progress-label {
  display: flex;
  justify-content: space-between;
  font-size: var(--text-xs);
  color: var(--text-muted);
  margin-bottom: var(--space-2);
}

.progress-bar {
  height: 4px;
  background: var(--bg-elevated);
  border-radius: var(--radius-full);
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: var(--gradient-accent);
  border-radius: var(--radius-full);
  width: 0%;
  transition: width var(--transition-slow);
}

/* Sidebar nav tree */
.sidebar-nav {
  flex: 1;
  overflow-y: auto;
  padding: var(--space-3) 0;
}

.chapter-group {
  margin-bottom: var(--space-1);
}

.chapter-group-header {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  padding: var(--space-2) var(--space-5);
  cursor: pointer;
  user-select: none;
  transition: background var(--transition-fast);
  border-radius: 0;
}
.chapter-group-header:hover { background: var(--bg-elevated); }

.chapter-group-toggle {
  width: 16px;
  height: 16px;
  color: var(--text-muted);
  transition: transform var(--transition-fast);
  flex-shrink: 0;
}
.chapter-group.open .chapter-group-toggle { transform: rotate(90deg); }

.chapter-group-title {
  font-size: var(--text-xs);
  font-weight: 700;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--text-muted);
  flex: 1;
}

.chapter-group-count {
  font-size: var(--text-xs);
  color: var(--text-muted);
  background: var(--bg-elevated);
  padding: 1px 6px;
  border-radius: var(--radius-full);
}

.lesson-list {
  display: none;
  padding-bottom: var(--space-2);
}
.chapter-group.open .lesson-list { display: block; }

.lesson-item {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  padding: var(--space-2) var(--space-5) var(--space-2) var(--space-10);
  cursor: pointer;
  transition: all var(--transition-fast);
  border-radius: 0;
  text-decoration: none;
  color: var(--text-secondary);
  font-size: var(--text-sm);
  position: relative;
}
.lesson-item:hover {
  background: var(--bg-elevated);
  color: var(--text-primary);
}
.lesson-item.active {
  background: rgba(124, 58, 237, 0.15);
  color: var(--accent-2);
}
.lesson-item.active::before {
  content: '';
  position: absolute;
  left: 0; top: 4px; bottom: 4px;
  width: 3px;
  background: var(--gradient-accent);
  border-radius: 0 var(--radius-full) var(--radius-full) 0;
}

.lesson-item-status {
  width: 18px;
  height: 18px;
  border-radius: 50%;
  border: 1.5px solid var(--border-muted);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  transition: all var(--transition-fast);
}
.lesson-item.done .lesson-item-status {
  background: var(--gradient-accent);
  border-color: transparent;
}
.lesson-item.done .lesson-item-status::after {
  content: '✓';
  font-size: 10px;
  color: white;
  font-weight: 700;
}
.lesson-item.active .lesson-item-status { border-color: var(--accent-2); }

.lesson-item-title {
  flex: 1;
  line-height: 1.3;
}

/* Sidebar Footer */
.sidebar-footer {
  padding: var(--space-4) var(--space-5);
  border-top: 1px solid var(--border-subtle);
  flex-shrink: 0;
}

.sidebar-footer-link {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-sm);
  color: var(--text-muted);
  transition: color var(--transition-fast);
}
.sidebar-footer-link:hover { color: var(--text-primary); }

/* ── Main Content Area ─────────────────────────────────────── */
.content-area {
  flex: 1;
  display: flex;
  flex-direction: column;
  overflow: hidden;
  min-width: 0;
}

/* Top bar */
.content-topbar {
  display: flex;
  align-items: center;
  gap: var(--space-4);
  padding: var(--space-3) var(--space-6);
  background: var(--bg-surface);
  border-bottom: 1px solid var(--border-subtle);
  flex-shrink: 0;
}

.topbar-toggle {
  width: 32px;
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-sm);
  color: var(--text-muted);
  transition: all var(--transition-fast);
  flex-shrink: 0;
}
.topbar-toggle:hover { background: var(--bg-elevated); color: var(--text-primary); }

.topbar-breadcrumb {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  flex: 1;
  min-width: 0;
}

.breadcrumb-chapter {
  font-size: var(--text-sm);
  color: var(--text-muted);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.breadcrumb-sep {
  color: var(--text-muted);
  flex-shrink: 0;
}

.breadcrumb-lesson {
  font-size: var(--text-sm);
  color: var(--text-secondary);
  font-weight: 500;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.topbar-actions {
  display: flex;
  align-items: center;
  gap: var(--space-2);
}

/* ── Lesson Content ────────────────────────────────────────── */
.content-main {
  flex: 1;
  overflow-y: auto;
}

.lesson-container {
  max-width: 780px;
  margin: 0 auto;
  padding: var(--space-12) var(--space-8);
}

/* Welcome / Empty state */
.welcome-state {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 70vh;
  text-align: center;
  padding: var(--space-8);
}

.welcome-icon {
  font-size: 72px;
  margin-bottom: var(--space-6);
  animation: float 5s ease-in-out infinite;
}

.welcome-title {
  font-size: var(--text-3xl);
  font-weight: 800;
  letter-spacing: -0.02em;
  margin-bottom: var(--space-4);
}

.welcome-desc {
  font-size: var(--text-lg);
  color: var(--text-secondary);
  max-width: 420px;
  margin-bottom: var(--space-8);
  line-height: 1.7;
}

/* Lesson header */
.lesson-header {
  margin-bottom: var(--space-10);
  padding-bottom: var(--space-8);
  border-bottom: 1px solid var(--border-subtle);
}

.lesson-chapter-tag {
  font-size: var(--text-xs);
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--accent-2);
  margin-bottom: var(--space-3);
  display: block;
}

.lesson-title {
  font-size: clamp(var(--text-2xl), 3vw, var(--text-4xl));
  font-weight: 800;
  letter-spacing: -0.02em;
  line-height: 1.2;
  margin-bottom: var(--space-4);
}

.lesson-meta {
  display: flex;
  align-items: center;
  gap: var(--space-4);
  flex-wrap: wrap;
}

.lesson-meta-item {
  display: flex;
  align-items: center;
  gap: var(--space-1);
  font-size: var(--text-xs);
  color: var(--text-muted);
}

/* Theory content */
.lesson-theory {
  line-height: 1.85;
  color: var(--text-secondary);
}

/* Image / Figures */
.lesson-fig {
  margin: var(--space-8) 0;
  text-align: center;
}

.lesson-fig img {
  max-width: 100%;
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-md);
  border: 1px solid var(--border-subtle);
  display: block;
  margin: 0 auto;
}

.lesson-fig figcaption {
  font-size: var(--text-xs);
  color: var(--text-muted);
  margin-top: var(--space-3);
  font-style: italic;
}

/* Image Placeholder Style */
.fig-placeholder {
  width: 100%;
  aspect-ratio: 16 / 9;
  background: var(--bg-elevated);
  border: 2px dashed var(--border-muted);
  border-radius: var(--radius-md);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  color: var(--text-muted);
  gap: var(--space-3);
  transition: all var(--transition-fast);
}
.fig-placeholder:hover {
  border-color: var(--accent-2);
  background: var(--bg-hover);
  color: var(--text-secondary);
}
.fig-placeholder-icon {
  font-size: 32px;
  opacity: 0.5;
}
.fig-placeholder-text {
  font-size: var(--text-sm);
  font-weight: 500;
}
.fig-placeholder-path {
  font-family: var(--font-mono);
  font-size: 11px;
  background: rgba(0,0,0,0.2);
  padding: 2px 8px;
  border-radius: 4px;
}

/* Theory content updates */
.lesson-theory h2 {
  font-size: var(--text-2xl);
  font-weight: 700;
  color: var(--text-primary);
  margin: var(--space-10) 0 var(--space-4);
  letter-spacing: -0.01em;
}

.lesson-theory h3 {
  font-size: var(--text-xl);
  font-weight: 600;
  color: var(--text-primary);
  margin: var(--space-8) 0 var(--space-3);
}

.lesson-theory p {
  margin-bottom: var(--space-5);
}

.lesson-theory strong {
  color: var(--text-primary);
  font-weight: 600;
}

.lesson-theory em {
  color: var(--text-accent);
  font-style: normal;
}

.lesson-theory ul, .lesson-theory ol {
  list-style: disc;
  padding-left: var(--space-6);
  margin-bottom: var(--space-5);
}

.lesson-theory ol { list-style: decimal; }

.lesson-theory li {
  margin-bottom: var(--space-2);
}

.lesson-theory code {
  font-family: var(--font-mono);
  font-size: 0.85em;
  color: var(--accent-2);
  background: rgba(124, 58, 237, 0.12);
  padding: 2px 6px;
  border-radius: 4px;
  border: 1px solid rgba(124, 58, 237, 0.2);
}

.lesson-theory blockquote {
  border-left: 3px solid var(--accent-1);
  padding: var(--space-4) var(--space-6);
  background: rgba(124, 58, 237, 0.05);
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  margin: var(--space-6) 0;
  color: var(--text-secondary);
}

.lesson-theory blockquote p { margin: 0; }

/* Callout boxes */
.callout {
  padding: var(--space-4) var(--space-5);
  border-radius: var(--radius-md);
  margin: var(--space-6) 0;
  display: flex;
  gap: var(--space-3);
}
.callout-icon { font-size: 18px; flex-shrink: 0; margin-top: 1px; }
.callout-body { flex: 1; }
.callout-title {
  font-weight: 600;
  font-size: var(--text-sm);
  margin-bottom: var(--space-1);
}
.callout-text { font-size: var(--text-sm); line-height: 1.6; }

.callout-info {
  background: rgba(37, 99, 235, 0.1);
  border: 1px solid rgba(37, 99, 235, 0.2);
  color: #93c5fd;
}
.callout-tip {
  background: rgba(16, 185, 129, 0.1);
  border: 1px solid rgba(16, 185, 129, 0.2);
  color: #6ee7b7;
}
.callout-warning {
  background: rgba(251, 191, 36, 0.1);
  border: 1px solid rgba(251, 191, 36, 0.2);
  color: #fde68a;
}

/* ── Quiz Section ──────────────────────────────────────────── */
.quiz-section {
  margin-top: var(--space-16);
  padding-top: var(--space-10);
  border-top: 1px solid var(--border-subtle);
  animation: fadeIn 0.5s ease;
}

.quiz-header {
  display: flex;
  align-items: center;
  gap: var(--space-4);
  margin-bottom: var(--space-8);
}

.quiz-icon {
  width: 40px;
  height: 40px;
  border-radius: var(--radius-md);
  background: var(--gradient-accent-soft);
  border: 1px solid var(--border-accent);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 20px;
  flex-shrink: 0;
}

.quiz-title {
  font-size: var(--text-2xl);
  font-weight: 700;
  letter-spacing: -0.01em;
}

.quiz-progress-text {
  font-size: var(--text-sm);
  color: var(--text-muted);
  margin-left: auto;
}

/* Question card */
.quiz-question-card {
  background: var(--bg-elevated);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: var(--space-8);
  margin-bottom: var(--space-6);
  animation: fadeUp 0.3s ease;
}

.quiz-question-number {
  font-size: var(--text-xs);
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--accent-2);
  margin-bottom: var(--space-4);
}

.quiz-question-text {
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--text-primary);
  line-height: 1.5;
  margin-bottom: var(--space-6);
}

.quiz-options {
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
}

.quiz-option {
  display: flex;
  align-items: flex-start;
  gap: var(--space-4);
  padding: var(--space-4) var(--space-5);
  border: 1.5px solid var(--border-muted);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-fast);
  text-align: left;
  color: var(--text-secondary);
  font-size: var(--text-sm);
  line-height: 1.5;
  background: transparent;
  width: 100%;
}
.quiz-option:hover:not(:disabled) {
  border-color: var(--accent-2);
  background: rgba(124, 58, 237, 0.08);
  color: var(--text-primary);
}
.quiz-option .option-letter {
  width: 24px;
  height: 24px;
  border-radius: 50%;
  border: 1.5px solid currentColor;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: var(--text-xs);
  font-weight: 700;
  flex-shrink: 0;
  transition: all var(--transition-fast);
}

.quiz-option.correct {
  border-color: #4ade80;
  background: rgba(74, 222, 128, 0.08);
  color: #4ade80;
}
.quiz-option.correct .option-letter {
  background: #4ade80;
  border-color: #4ade80;
  color: #000;
}

.quiz-option.wrong {
  border-color: #f87171;
  background: rgba(248, 113, 113, 0.08);
  color: #f87171;
}
.quiz-option.wrong .option-letter {
  background: #f87171;
  border-color: #f87171;
  color: #000;
}

.quiz-option:disabled { cursor: not-allowed; opacity: 0.8; }

/* Quiz explanation */
.quiz-explanation {
  padding: var(--space-4) var(--space-5);
  background: rgba(124, 58, 237, 0.08);
  border: 1px solid var(--border-accent);
  border-radius: var(--radius-md);
  font-size: var(--text-sm);
  color: var(--text-secondary);
  line-height: 1.6;
  margin-top: var(--space-4);
  display: none;
}
.quiz-explanation.visible { display: block; animation: fadeUp 0.3s ease; }

.quiz-explanation strong { color: var(--accent-2); }

/* Quiz navigation */
.quiz-nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-top: var(--space-6);
}

/* Quiz result */
.quiz-result {
  text-align: center;
  padding: var(--space-12);
  background: var(--bg-elevated);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  animation: fadeUp 0.4s ease;
}

.quiz-result-emoji { font-size: 56px; margin-bottom: var(--space-4); }
.quiz-result-score {
  font-size: var(--text-5xl);
  font-weight: 800;
  letter-spacing: -0.03em;
  margin-bottom: var(--space-2);
}
.quiz-result-label {
  font-size: var(--text-sm);
  color: var(--text-muted);
  margin-bottom: var(--space-6);
}
.quiz-result-actions {
  display: flex;
  gap: var(--space-3);
  justify-content: center;
  flex-wrap: wrap;
}

/* ── Lesson Navigation ─────────────────────────────────────── */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  gap: var(--space-4);
  margin-top: var(--space-16);
  padding-top: var(--space-8);
  border-top: 1px solid var(--border-subtle);
}

.lesson-nav-btn {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  padding: var(--space-4) var(--space-5);
  background: var(--bg-elevated);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  transition: all var(--transition-fast);
  flex: 1;
  max-width: 280px;
  cursor: pointer;
  color: inherit;
  text-decoration: none;
}
.lesson-nav-btn:hover {
  border-color: var(--border-accent);
  background: var(--bg-hover);
}
.lesson-nav-btn.next { margin-left: auto; text-align: right; flex-direction: row-reverse; }
.lesson-nav-btn:disabled { opacity: 0.4; pointer-events: none; }

.lesson-nav-dir {
  font-size: var(--text-xs);
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  font-weight: 600;
}
.lesson-nav-title {
  font-size: var(--text-sm);
  font-weight: 500;
  color: var(--text-primary);
  margin-top: 2px;
}

/* ── Responsive ────────────────────────────────────────────── */
@media (max-width: 768px) {
  .sidebar {
    position: fixed;
    top: 0; left: 0; bottom: 0;
    z-index: 200;
    transform: translateX(-100%);
    transition: transform var(--transition-normal);
  }
  .sidebar.mobile-open {
    transform: translateX(0);
    width: 280px;
    min-width: 280px;
  }
  .sidebar-backdrop {
    position: fixed;
    inset: 0;
    background: rgba(0,0,0,0.6);
    z-index: 199;
    display: none;
  }
  .sidebar-backdrop.visible { display: block; }

  .lesson-container { padding: var(--space-6) var(--space-4); }
  .quiz-question-card { padding: var(--space-5); }
  .lesson-nav { flex-direction: column; }
  .lesson-nav-btn { max-width: 100%; }
  .lesson-nav-btn.next { margin-left: 0; }
}