/* ── Lesson page ── */

.lesson-content {
  max-width: 840px;
}

.lesson-sections {
  display: grid;
  gap: 1.35rem;
}

.lesson-block {
  padding: 1.45rem 1.5rem;
  border-radius: var(--radius-lg);
  background: rgba(255, 255, 255, 0.95);
  border: 1px solid var(--border);
  box-shadow: var(--shadow-sm);
  transition: transform 0.28s ease, box-shadow 0.28s ease;
  position: relative;
  overflow: hidden;
}

.lesson-block::before {
  content: "";
  position: absolute;
  inset-inline: 0;
  top: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--accent), var(--violet));
  opacity: 0.75;
}

.lesson-block:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow);
}

#pdf::before { background: linear-gradient(90deg, var(--sky), #38bdf8); }
#explanation::before { background: linear-gradient(90deg, var(--accent), var(--violet)); }
#video::before { background: linear-gradient(90deg, var(--rose), #fb7185); }
#book-exercises::before { background: linear-gradient(90deg, var(--emerald), #34d399); }
#extra-exercises::before { background: linear-gradient(90deg, var(--amber), #fbbf24); }
#past-exams::before { background: linear-gradient(90deg, var(--violet), #a78bfa); }
#comments::before { background: linear-gradient(90deg, var(--sky), var(--accent)); }

.lesson-block-title {
  display: flex;
  align-items: center;
  gap: 0.65rem;
  margin: 0 0 1.1rem;
  font-size: 1.18rem;
  font-weight: 800;
  color: var(--text);
}

.lesson-block-icon {
  display: grid;
  place-items: center;
  width: 2.35rem;
  height: 2.35rem;
  border-radius: 0.7rem;
  background: linear-gradient(135deg, var(--accent-soft), rgba(124, 58, 237, 0.1));
  font-size: 1.05rem;
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.85);
}

#pdf .lesson-block-icon { background: linear-gradient(135deg, rgba(14, 165, 233, 0.15), rgba(56, 189, 248, 0.1)); }
#explanation .lesson-block-icon { background: linear-gradient(135deg, var(--accent-soft), rgba(124, 58, 237, 0.12)); }
#video .lesson-block-icon { background: linear-gradient(135deg, rgba(244, 63, 94, 0.12), rgba(251, 113, 133, 0.08)); }
#book-exercises .lesson-block-icon { background: linear-gradient(135deg, rgba(16, 185, 129, 0.14), rgba(52, 211, 153, 0.1)); }
#extra-exercises .lesson-block-icon { background: linear-gradient(135deg, rgba(245, 158, 11, 0.14), rgba(251, 191, 36, 0.1)); }
#past-exams .lesson-block-icon { background: linear-gradient(135deg, rgba(124, 58, 237, 0.14), rgba(167, 139, 250, 0.1)); }
#comments .lesson-block-icon { background: linear-gradient(135deg, rgba(14, 165, 233, 0.12), var(--accent-soft)); }

.lesson-text p {
  margin: 0 0 0.85rem;
  color: var(--muted);
  line-height: 1.8;
}

.explanation-steps {
  display: grid;
  gap: 1.15rem;
  counter-reset: explanation-card;
}

.explanation-progress {
  display: flex;
  flex-direction: column;
  gap: 0.55rem;
  margin-bottom: 1.15rem;
  padding: 0.85rem 1rem 0.95rem;
  border-radius: var(--radius);
  background: #fff;
  border: 1px solid rgba(79, 70, 229, 0.18);
  box-shadow: 0 6px 20px rgba(79, 70, 229, 0.08);
}

.explanation-progress-track {
  position: relative;
  height: 0.45rem;
  border-radius: 999px;
  background: rgba(79, 70, 229, 0.1);
  overflow: hidden;
}

.explanation-progress-fill {
  display: block;
  height: 100%;
  border-radius: inherit;
  background: linear-gradient(90deg, var(--accent), var(--violet));
  box-shadow: 0 0 12px var(--accent-glow);
  transition: width 0.45s cubic-bezier(0.22, 1, 0.36, 1);
}

.explanation-progress-label {
  font-size: 0.84rem;
  font-weight: 800;
  color: var(--accent);
  letter-spacing: 0.01em;
}

.explanation-step {
  position: relative;
  padding: 0;
  border-radius: var(--radius-lg);
  background: #fff;
  border: 1px solid rgba(79, 70, 229, 0.16);
  box-shadow:
    0 1px 0 rgba(255, 255, 255, 0.65) inset,
    0 12px 32px rgba(15, 23, 42, 0.08);
  overflow: hidden;
}

.explanation-step::before {
  content: "";
  display: block;
  height: 4px;
  background: linear-gradient(90deg, var(--accent), var(--violet), #818cf8);
}

.explanation-step::after {
  content: "";
  position: absolute;
  top: 4px;
  inset-inline-end: 0;
  width: 7rem;
  height: 7rem;
  background: radial-gradient(circle at 100% 0%, rgba(124, 58, 237, 0.08), transparent 68%);
  pointer-events: none;
}

.explanation-step.step-hidden {
  display: none;
}

.explanation-step.step-visible {
  animation: fadeUp 0.42s cubic-bezier(0.22, 1, 0.36, 1) both;
}

.explanation-step-title {
  display: flex;
  align-items: center;
  gap: 0.8rem;
  margin: 0;
  padding: 1.15rem 1.4rem 0.85rem;
  font-size: 1.12rem;
  font-weight: 800;
  color: var(--text);
  line-height: 1.45;
}

.explanation-step-title::before {
  counter-increment: explanation-card;
  content: counter(explanation-card);
  flex-shrink: 0;
  width: 2.15rem;
  height: 2.15rem;
  display: grid;
  place-items: center;
  border-radius: 0.7rem;
  background: linear-gradient(135deg, var(--accent), var(--violet));
  color: #fff;
  font-size: 0.92rem;
  font-weight: 800;
  box-shadow: 0 4px 14px var(--accent-glow);
}

.explanation-step-body {
  padding: 0 1.4rem 0.35rem;
}

.explanation-step-body p {
  margin: 0 0 0.8rem;
  color: var(--muted);
  line-height: 1.82;
}

.explanation-step-body p:last-child {
  margin-bottom: 0;
}

.explanation-step-body .md-subheading {
  margin: 1.15rem 0 0.6rem;
  padding-inline-start: 0.65rem;
  border-inline-start: 3px solid var(--accent);
  font-size: 1rem;
  font-weight: 800;
  color: var(--text);
}

.explanation-step-body .md-hr {
  border: 0;
  border-top: 1px dashed rgba(79, 70, 229, 0.2);
  margin: 1.1rem 0;
}

.explanation-step-body .table-scroll-wrap {
  margin-bottom: 1rem;
  border-radius: 0.75rem;
  overflow-x: auto;
  overflow-y: hidden;
  -webkit-overflow-scrolling: touch;
  overscroll-behavior-x: contain;
  touch-action: pan-x pan-y;
  border: 1px solid rgba(79, 70, 229, 0.12);
  box-shadow: 0 4px 16px rgba(15, 23, 42, 0.05);
}

.explanation-step-body table.md-table {
  margin-bottom: 0;
  border: none;
  border-radius: 0;
  overflow: visible;
  box-shadow: none;
}

.explanation-step-body table.md-table th {
  background: linear-gradient(135deg, var(--accent-soft), rgba(124, 58, 237, 0.08));
  color: var(--accent);
  font-weight: 800;
}

.explanation-step-body table.md-table tbody tr:hover {
  background: rgba(79, 70, 229, 0.04);
}

.rich-content figure.md-figure {
  margin: 1rem 0;
  text-align: center;
}

.rich-content figure.md-figure img {
  display: block;
  max-width: min(100%, 420px);
  height: auto;
  margin: 0 auto;
  border-radius: 12px;
  border: 1px solid rgba(79, 70, 229, 0.12);
  box-shadow: 0 8px 24px rgba(15, 23, 42, 0.08);
  cursor: zoom-in;
  touch-action: pan-y;
  -webkit-user-drag: none;
}

.rich-content figure.md-figure figcaption {
  margin-top: 0.55rem;
  font-size: 0.88rem;
  color: var(--muted);
}

.rich-content table.md-table img.md-inline-img,
.rich-content table.solution-steps img.md-inline-img {
  display: block;
  max-width: min(100%, 220px);
  height: auto;
  margin: 0.15rem auto;
  border-radius: 8px;
  border: 1px solid rgba(79, 70, 229, 0.12);
  cursor: zoom-in;
}

.explanation-step-body img,
.lesson-v2-exercise-group .exercise-q img {
  cursor: zoom-in;
}

.explanation-step-actions {
  display: flex;
  justify-content: flex-start;
  margin: 0.85rem 1.4rem 1.3rem;
  padding-top: 1rem;
  border-top: 1px solid rgba(79, 70, 229, 0.1);
}

.btn-reveal-explanation {
  appearance: none;
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  border: none;
  border-radius: 999px;
  padding: 0.55rem 1.25rem;
  font: inherit;
  font-weight: 800;
  font-size: 0.9rem;
  cursor: pointer;
  background: linear-gradient(135deg, var(--accent), var(--violet));
  color: #fff;
  box-shadow: 0 6px 18px var(--accent-glow);
  transition: transform 0.2s ease, box-shadow 0.2s ease, filter 0.2s ease;
}

.btn-reveal-explanation::after {
  content: "←";
  font-size: 1rem;
  line-height: 1;
  opacity: 0.92;
}

.btn-reveal-explanation:hover {
  transform: translateY(-2px);
  box-shadow: 0 10px 24px var(--accent-glow);
  filter: brightness(1.04);
}

.comprehension-check {
  position: relative;
  overflow: hidden;
  margin-top: 0.85rem;
  padding: 0;
  border-radius: calc(var(--radius-lg) - 2px);
  border: 1px solid rgba(245, 158, 11, 0.28);
  background:
    linear-gradient(165deg, #fffbeb 0%, #fff7ed 38%, #ffffff 100%),
    radial-gradient(circle at 0% 0%, rgba(251, 191, 36, 0.12), transparent 55%);
  box-shadow:
    0 1px 0 rgba(255, 255, 255, 0.9) inset,
    0 8px 22px rgba(245, 158, 11, 0.1);
}

.comprehension-check::before {
  content: "";
  position: absolute;
  inset-inline: 0;
  top: 0;
  height: 3px;
  background: linear-gradient(90deg, #fbbf24, #f59e0b, #f97316);
}

.comprehension-check-header {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.6rem;
  padding: 0.65rem 0.9rem 0.35rem;
  border-bottom: none;
  background: linear-gradient(135deg, rgba(251, 191, 36, 0.14), rgba(245, 158, 11, 0.04));
}

.comprehension-check-heading {
  min-width: 0;
  display: flex;
  align-items: center;
}

.comprehension-check-subtitle {
  margin: 0.15rem 0 0;
  font-size: 0.78rem;
  font-weight: 700;
  color: rgba(146, 64, 14, 0.72);
}

.comprehension-check-icon {
  flex-shrink: 0;
  width: 1.85rem;
  height: 1.85rem;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 0.55rem;
  background: linear-gradient(135deg, #fbbf24, #ea580c);
  color: #fff;
  font-family: "Apple Color Emoji", "Segoe UI Emoji", "Noto Color Emoji", sans-serif;
  font-size: 1.05rem;
  line-height: 1;
  text-align: center;
  transform-origin: center center;
  box-shadow: 0 4px 12px rgba(245, 158, 11, 0.3);
  animation: checkIconPulse 2.8s ease-in-out infinite;
}

@keyframes checkIconPulse {
  0%, 100% { transform: scale(1); }
  50% { transform: scale(1.04); }
}

.comprehension-check.check-done {
  border-color: rgba(16, 185, 129, 0.32);
  background: linear-gradient(165deg, #ecfdf5 0%, #f0fdf4 50%, #ffffff 100%);
  box-shadow:
    0 1px 0 rgba(255, 255, 255, 0.85) inset,
    0 10px 28px rgba(16, 185, 129, 0.12);
}

.comprehension-check.check-done .comprehension-check-header {
  border-bottom-color: rgba(16, 185, 129, 0.18);
  background: linear-gradient(135deg, rgba(52, 211, 153, 0.16), rgba(16, 185, 129, 0.06));
}

.comprehension-check.check-done .comprehension-check-icon {
  background: linear-gradient(135deg, #10b981, #059669);
  box-shadow: 0 4px 12px rgba(16, 185, 129, 0.3);
}

.comprehension-check.check-revealed {
  animation: checkBoxCelebrate 0.32s cubic-bezier(0.22, 1, 0.36, 1);
}

.comprehension-check.check-revealed::after {
  content: "✨";
  position: absolute;
  top: 0.85rem;
  inset-inline-start: 0.9rem;
  font-size: 1.15rem;
  opacity: 0;
  animation: checkSparkle 0.4s ease 0.05s forwards;
  pointer-events: none;
}

.comprehension-check.check-animating::before {
  content: "";
  position: absolute;
  inset: 0;
  background: radial-gradient(circle at 50% 20%, rgba(16, 185, 129, 0.22), transparent 58%);
  opacity: 0;
  animation: checkGlowPulse 0.35s ease forwards;
  pointer-events: none;
}

.comprehension-check-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.2rem;
  margin: 0 0.65rem 0.45rem;
  padding: 0.2rem 0.55rem;
  border-radius: 999px;
  font-size: 0.68rem;
  font-weight: 800;
  color: #047857;
  background: linear-gradient(135deg, #d1fae5, #a7f3d0);
  border: 1px solid rgba(16, 185, 129, 0.35);
  opacity: 0;
  transform: translateY(6px) scale(0.98);
  transition: opacity 0.2s ease, transform 0.22s ease;
}

.comprehension-check-badge.is-visible {
  opacity: 1;
  transform: translateY(0) scale(1);
  transition: opacity 0.2s ease, transform 0.25s ease;
}

.comprehension-check-title {
  margin: 0;
  font-size: 0.92rem;
  font-weight: 800;
  line-height: 1.85rem;
  color: #92400e;
}

.comprehension-check.check-done .comprehension-check-title {
  color: #047857;
}

.comprehension-check.check-done .comprehension-check-subtitle {
  color: rgba(4, 120, 87, 0.75);
}

.comprehension-check-answer-label {
  display: inline-flex;
  align-items: center;
  margin-bottom: 0.4rem;
  padding: 0.15rem 0.45rem;
  border-radius: 999px;
  font-size: 0.72rem;
  font-weight: 800;
  letter-spacing: 0.02em;
  color: #047857;
  background: rgba(16, 185, 129, 0.14);
  border: 1px solid rgba(16, 185, 129, 0.24);
}

.comprehension-check-question {
  margin: 0 0.85rem 0.2rem;
  padding: 0.55rem 0.75rem;
  border-radius: calc(var(--radius) - 2px);
  border: 1px solid rgba(245, 158, 11, 0.2);
  border-inline-start: 3px solid #f59e0b;
  background: rgba(255, 255, 255, 0.94);
  color: var(--text);
  box-shadow: none;
  font-size: inherit;
  line-height: 1.7;
}

.comprehension-check-question p {
  margin: 0 0 0.45rem;
  font-size: inherit;
}

.comprehension-check-question table.md-table {
  font-size: inherit;
}

.comprehension-check-prompt {
  margin: 0 1.1rem 0.55rem;
  padding: 0.45rem 0.75rem;
  border-radius: 999px;
  font-size: 0.78rem;
  font-weight: 700;
  color: rgba(146, 64, 14, 0.85);
  background: rgba(255, 255, 255, 0.72);
  border: 1px dashed rgba(245, 158, 11, 0.28);
  text-align: center;
}

.comprehension-check-question p:last-child {
  margin-bottom: 0;
}

.comprehension-check-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
  padding: 0 0.85rem 0.75rem;
}

.comprehension-check-next-wrap {
  display: flex;
  justify-content: flex-start;
  padding: 0.35rem 0.85rem 0.85rem;
  margin-top: -0.15rem;
}

.comprehension-check-next-wrap.hidden,
.comprehension-check-next-wrap[hidden] {
  display: none !important;
}

.comprehension-check-answer.is-visible + .comprehension-check-next-wrap {
  margin-top: 0.15rem;
}

.btn-check-reveal,
.btn-check-next {
  appearance: none;
  border-radius: 999px;
  padding: 0.45rem 0.95rem;
  font: inherit;
  font-weight: 800;
  font-size: 0.84rem;
  cursor: pointer;
  transition: background 0.2s ease, transform 0.2s ease, box-shadow 0.2s ease, border-color 0.2s ease;
}

.btn-check-reveal {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  border: none;
  background: linear-gradient(135deg, var(--accent), var(--violet));
  color: #fff;
  box-shadow: 0 6px 18px var(--accent-glow);
  flex: 1 1 10rem;
  justify-content: center;
}

.btn-check-reveal::before {
  content: "💡";
  font-size: 0.95rem;
  line-height: 1;
}

.btn-check-reveal:hover:not(:disabled) {
  transform: translateY(-2px);
  box-shadow: 0 10px 24px var(--accent-glow);
  filter: brightness(1.04);
}

.btn-check-next {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.3rem;
  border: 1px solid rgba(100, 116, 139, 0.28);
  background: rgba(255, 255, 255, 0.88);
  color: var(--muted);
  flex: 0 1 auto;
}

.btn-check-next::before {
  content: "⏭";
  font-size: 0.9rem;
  line-height: 1;
}

.btn-check-next:hover {
  background: #fff;
  border-color: rgba(100, 116, 139, 0.42);
  color: var(--text);
  transform: translateY(-1px);
}

.btn-check-next.hidden,
.btn-check-reveal.hidden,
.comprehension-check-actions .btn-check-reveal[hidden],
.comprehension-check-next-wrap .btn-check-next[hidden] {
  display: none !important;
}

.comprehension-check-answer {
  margin: 0.35rem 0.85rem 0.75rem;
  padding: 0.55rem 0.75rem;
  border-radius: calc(var(--radius) - 2px);
  border: 1px solid rgba(16, 185, 129, 0.22);
  border-inline-start: 3px solid #10b981;
  background: linear-gradient(135deg, rgba(236, 253, 245, 0.95), rgba(255, 255, 255, 0.98));
  color: var(--text);
  opacity: 0;
  transform: translateY(8px);
  font-size: inherit;
  line-height: 1.7;
  transition: opacity 0.22s ease, transform 0.22s ease, box-shadow 0.22s ease, border-color 0.22s ease;
}

.comprehension-check-answer p {
  margin: 0 0 0.45rem;
  font-size: inherit;
}

.comprehension-check-answer.is-preparing {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  opacity: 0;
  pointer-events: none;
  margin: 0;
  padding: 0;
  border: none;
}

.comprehension-check-answer.is-visible {
  opacity: 1;
  transform: translateY(0);
  border-color: rgba(16, 185, 129, 0.35);
  background: linear-gradient(135deg, #ecfdf5 0%, #d1fae5 100%);
  box-shadow: 0 8px 22px rgba(16, 185, 129, 0.14);
}

.comprehension-check-answer p:last-child {
  margin-bottom: 0;
}

.btn-check-reveal.is-popping {
  animation: checkBtnPop 0.45s cubic-bezier(0.22, 1, 0.36, 1);
}

@keyframes checkAnswerReveal {
  0% {
    opacity: 0;
    transform: translateY(14px) scale(0.97);
  }
  60% {
    opacity: 1;
    transform: translateY(-3px) scale(1.02);
  }
  100% {
    opacity: 1;
    transform: translateY(0) scale(1);
  }
}

@keyframes checkBoxCelebrate {
  0% { transform: scale(1); }
  35% { transform: scale(1.015); box-shadow: 0 8px 28px rgba(16, 185, 129, 0.2); }
  100% { transform: scale(1); }
}

@keyframes checkGlowPulse {
  0% { opacity: 0; }
  30% { opacity: 1; }
  100% { opacity: 0; }
}

@keyframes checkSparkle {
  0% { opacity: 0; transform: scale(0.6) rotate(-12deg); }
  40% { opacity: 1; transform: scale(1.15) rotate(8deg); }
  100% { opacity: 0; transform: scale(0.9) rotate(18deg); }
}

@keyframes badgePop {
  0% { transform: translateY(8px) scale(0.92); }
  55% { transform: translateY(-2px) scale(1.06); }
  100% { transform: translateY(0) scale(1); }
}

@keyframes checkBtnPop {
  0% { transform: scale(1); }
  45% { transform: scale(1.08); }
  100% { transform: scale(0.95); opacity: 0.6; }
}

@media (prefers-reduced-motion: reduce) {
  .comprehension-check-icon {
    animation: none !important;
  }

  .comprehension-check.check-revealed,
  .comprehension-check.check-animating::before,
  .comprehension-check.check-revealed::after,
  .comprehension-check-answer.is-visible,
  .comprehension-check-badge.is-visible,
  .btn-check-reveal.is-popping {
    animation: none !important;
    transition: none !important;
  }

  .comprehension-check-answer.is-visible {
    opacity: 1;
    transform: none;
  }

  .comprehension-check-badge.is-visible {
    opacity: 1;
    transform: none;
  }
}

.rich-content {
  color: var(--text);
  line-height: 1.8;
}

.rich-content p {
  margin: 0 0 0.85rem;
  color: inherit;
}

.rich-content p:last-child {
  margin-bottom: 0;
}

.rich-content pre.md-pre {
  margin: 0 0 1rem;
  padding: 0.85rem 1rem;
  overflow-x: auto;
  border-radius: 0.75rem;
  border: 1px solid var(--border);
  background: #f8fafc;
  direction: ltr;
  text-align: left;
}

.triangle-figure,
.line-segment-figure {
  margin: 0 0 1.25rem;
  padding: 1rem 1rem 0.75rem;
  border-radius: var(--radius);
  border: 1px solid rgba(79, 70, 229, 0.18);
  background: linear-gradient(160deg, #fafbff, #f5f7ff);
  box-shadow: var(--shadow-sm);
  text-align: center;
}

.triangle-figure svg,
.line-segment-figure svg {
  display: block;
  width: min(100%, 420px);
  height: auto;
  margin: 0 auto;
}

.line-segment-figure svg {
  width: min(100%, 480px);
}

.triangle-figure figcaption,
.line-segment-figure figcaption {
  margin-top: 0.65rem;
  font-size: 0.88rem;
  color: var(--muted);
  line-height: 1.6;
}

.rich-content pre.md-pre code {
  font-family: "IBM Plex Mono", "Courier New", monospace;
  font-size: 0.82rem;
  line-height: 1.45;
  white-space: pre;
  color: #0f172a;
}

.rich-content table.md-table {
  width: 100%;
  border-collapse: collapse;
  margin: 0 0 1rem;
  font-size: 0.92rem;
  direction: rtl;
}

.rich-content table.md-table th,
.rich-content table.md-table td {
  border: 1px solid var(--border);
  padding: 0.55rem 0.7rem;
  vertical-align: top;
  text-align: start;
  line-height: 1.55;
}

.rich-content table.md-table th {
  background: #f1f5f9;
  font-weight: 800;
}

.rich-content table.md-table tbody tr:nth-child(even) {
  background: rgba(248, 250, 252, 0.85);
}

.rich-content table.md-table mjx-container {
  direction: ltr;
  display: inline-block;
}

.rich-content ul,
.rich-content ol {
  margin: 0 0 0.85rem;
  padding-inline-start: 1.25rem;
}

.rich-content .math-tex {
  color: var(--accent);
  font-weight: 600;
}

.rich-content mjx-container {
  direction: ltr;
  display: inline-block;
  unicode-bidi: embed;
  text-align: left;
}

.rich-content mjx-container[display="true"] {
  display: block;
  margin: 0.65rem auto;
  text-align: center;
}

.rich-content mjx-container mjx-mtext {
  font-family: "Tajawal", sans-serif !important;
  direction: rtl;
  unicode-bidi: isolate;
}

.rich-content .solution-list {
  margin: 0;
  padding-inline-start: 1.5rem;
  list-style: decimal;
}

.rich-content .solution-list .solution-step-item {
  margin-bottom: 1rem;
  line-height: 1.75;
}

.rich-content .solution-list .step-note {
  display: block;
  margin-top: 0.35rem;
  color: var(--muted);
  font-size: 0.92em;
}

.lesson-text.rich-content {
  color: var(--muted);
}

.lesson-text p:last-child {
  margin-bottom: 0;
}

.pdf-wrap {
  border-radius: var(--radius);
  overflow: hidden;
  border: 1px solid var(--border);
  background: linear-gradient(160deg, #f8fafc, #eef2ff);
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.9);
}

.pdf-wrap iframe {
  display: block;
  width: 100%;
  height: min(520px, 70vh);
  border: none;
}

.pdf-viewer-wrap {
  border-radius: var(--radius);
  border: 1px solid var(--border);
  background: linear-gradient(160deg, #f8fafc, #eef2ff);
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.9);
  overflow: hidden;
  max-width: 100%;
  position: relative;
}

.pdf-viewer-loading {
  position: absolute;
  inset: 0;
  z-index: 2;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 1.25rem;
  background: inherit;
}

.pdf-viewer-wrap--loading .pdf-viewer-body--pending {
  visibility: hidden;
  pointer-events: none;
}

.pdf-page-canvas-placeholder {
  display: block;
  max-width: 100%;
  margin-inline: auto;
}

.pdf-viewer-wrap--ready .pdf-viewer-body {
  animation: pdfViewerFadeIn 0.2s ease both;
}

@keyframes pdfViewerFadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

.pdf-inline-toolbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.5rem 0.85rem;
  background: #f8fafc;
  border-bottom: 1px solid var(--border);
  gap: 0.5rem;
}

.pdf-inline-nav-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  padding: 0.38rem 0.85rem;
  border-radius: 999px;
  background: #ffffff;
  border: 1.5px solid #cbd5e1;
  color: #1d4ed8;
  font-size: 0.82rem;
  font-weight: 800;
  cursor: pointer;
  transition: all 0.15s ease;
}

.pdf-inline-nav-btn:hover:not(:disabled) {
  background: #eff6ff;
  border-color: #93c5fd;
  color: #1e40af;
}

.pdf-inline-nav-btn:disabled {
  opacity: 0.32;
  cursor: not-allowed;
}

.pdf-inline-counter {
  font-size: 0.84rem;
  font-weight: 800;
  color: #1e293b;
  direction: ltr;
  background: #eff6ff;
  padding: 0.2rem 0.65rem;
  border-radius: 999px;
  border: 1px solid #bfdbfe;
}

.pdf-scroll {
  overflow-x: auto;
  overflow-y: hidden;
  scroll-snap-type: x mandatory;
  -webkit-overflow-scrolling: touch;
  scroll-behavior: smooth;
  padding: 0.5rem 0;
  display: flex;
  flex-direction: row;
  align-items: center;
  gap: 0;
  width: 100%;
  max-height: none;
  direction: rtl;
  overscroll-behavior-x: contain;
  overscroll-behavior-y: auto;
  touch-action: pan-x pan-y pinch-zoom;
  -webkit-user-select: none;
  user-select: none;
}

.lesson-v2-slideshow-panel {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.lesson-v2-slideshow-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-bottom: 0.25rem;
}

.lesson-v2-slideshow-hint {
  margin: 0;
  font-size: 0.84rem;
  font-weight: 700;
  color: var(--muted);
}

.lesson-v2-slideshow-stack {
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

.lesson-v2-slideshow-block {
  width: 100%;
}

.lesson-v2-slideshow-viewer {
  width: 100%;
  border-radius: var(--radius-lg);
}

.pdf-scroll--vertical {
  max-height: min(85vh, 920px);
  overflow-x: hidden;
  overflow-y: auto !important;
  scroll-behavior: smooth;
  flex-direction: column;
  align-items: stretch;
  gap: 0.85rem;
  padding: 0.65rem 0.5rem;
  touch-action: pan-y pinch-zoom;
  -webkit-overflow-scrolling: touch;
  overscroll-behavior-y: contain;
  scrollbar-width: thin;
  scrollbar-color: rgba(37, 99, 235, 0.35) transparent;
}

.pdf-scroll--vertical .pdf-page {
  scroll-snap-stop: normal;
  flex: 0 0 auto;
  width: 100% !important;
  margin-bottom: 0.4rem;
}

.pdf-page {
  scroll-snap-align: start;
  scroll-snap-stop: always;
  flex: 0 0 100%;
  width: 100% !important;
  box-sizing: border-box;
  background: #fff;
  border-radius: 0.65rem;
  border: 1px solid var(--border);
  padding: 0.45rem 0.55rem 0.55rem;
  box-shadow: var(--shadow-sm);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 0;
}

.pdf-page-canvas-wrap,
.pdf-pinch-viewport {
  flex: 1 1 auto;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 100% !important;
  max-width: 100% !important;
  min-height: 0;
  max-height: none !important;
  cursor: zoom-in;
  border-radius: 0.35rem;
  transition: box-shadow 0.2s ease;
  overflow: hidden;
  touch-action: pan-x pan-y pinch-zoom;
}

.pdf-page-canvas-wrap.is-zoomed,
.pdf-pinch-viewport.is-zoomed {
  overflow: auto;
  max-height: min(88vh, 980px);
  touch-action: none;
  -webkit-overflow-scrolling: touch;
}

.pdf-pinch-inner {
  transform-origin: center center;
  display: flex;
  align-items: center;
  justify-content: center;
  will-change: transform;
  width: 100% !important;
}

.pdf-page-canvas-wrap:hover {
  box-shadow: inset 0 0 0 2px rgba(79, 70, 229, 0.18);
}

.pdf-page canvas {
  display: block;
  width: 100% !important;
  max-width: 100% !important;
  height: auto !important;
  max-height: none !important;
  border-radius: 0.35rem;
  box-shadow: 0 2px 12px rgba(30, 27, 75, 0.08);
  image-rendering: auto;
}

.pdf-page-label {
  margin: 0 0 0.35rem;
  font-size: 0.78rem;
  font-weight: 800;
  color: var(--muted);
  text-align: center;
}

.pdf-wrap-single iframe {
  height: min(88vh, 980px);
}

.pdf-loading,
.pdf-error {
  margin: 0;
  padding: 1.25rem;
  text-align: center;
  color: var(--muted);
  font-weight: 600;
}

.pdf-error {
  color: var(--danger, #dc2626);
}

.pdf-caption {
  margin: 0.75rem 0 0;
  font-size: 0.88rem;
  color: var(--muted);
  font-weight: 600;
}

.pdf-lightbox {
  position: fixed;
  inset: 0;
  z-index: 200;
  display: grid;
  place-items: center;
  padding: 1rem;
}

.pdf-lightbox[hidden] {
  display: none !important;
}

body.pdf-lightbox-open {
  overflow: hidden;
}

.pdf-lightbox-backdrop {
  position: absolute;
  inset: 0;
  border: none;
  padding: 0;
  background: rgba(15, 23, 42, 0.72);
  backdrop-filter: blur(6px);
  cursor: zoom-out;
}

.pdf-lightbox-panel {
  position: relative;
  z-index: 1;
  width: min(96vw, 1400px);
  max-height: min(94vh, 1200px);
  display: flex;
  flex-direction: column;
  gap: 0.55rem;
  padding: 0.85rem;
  border-radius: var(--radius-lg);
  background: #fff;
  border: 1px solid var(--border);
  box-shadow: var(--shadow-lg);
}

.pdf-lightbox-toolbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 0.65rem;
  padding-inline-end: 2.25rem;
}

.pdf-lightbox-nav {
  appearance: none;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.35rem;
  padding: 0.42rem 0.9rem;
  border-radius: 999px;
  border: 1.5px solid #bfdbfe;
  background: #eff6ff;
  color: #1d4ed8;
  font: inherit;
  font-size: 0.82rem;
  font-weight: 800;
  cursor: pointer;
  transition: all 0.2s ease;
}

.pdf-lightbox-nav:hover:not(:disabled) {
  background: #2563eb;
  color: #ffffff;
  border-color: #2563eb;
  box-shadow: 0 2px 8px rgba(37, 99, 235, 0.25);
}

.pdf-lightbox-nav:disabled {
  opacity: 0.35;
  cursor: not-allowed;
}

.pdf-lightbox-prev {
  justify-self: start;
}

.pdf-lightbox-next {
  justify-self: end;
}

.pdf-lightbox-center {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.25rem;
}

.pdf-lightbox-zoom-toolbar {
  display: inline-flex;
  align-items: center;
  background: rgba(255, 255, 255, 0.96);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  border: 1.5px solid #cbd5e1;
  border-radius: 999px;
  padding: 2px 6px;
  box-shadow: 0 4px 14px rgba(15, 23, 42, 0.08);
  gap: 4px;
  direction: ltr;
}

.pdf-lightbox-tool-btn {
  border: none;
  background: transparent;
  color: #1d4ed8;
  font-size: 1.15rem;
  font-weight: 800;
  height: 2rem;
  min-width: 2rem;
  padding: 0 0.4rem;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: 999px;
  cursor: pointer;
  line-height: 1;
  transition: all 0.15s ease;
}

.pdf-lightbox-tool-btn:hover:not(:disabled) {
  background: #eff6ff;
  color: #1e40af;
}

.pdf-lightbox-tool-btn:active:not(:disabled) {
  transform: scale(0.92);
}

.pdf-lightbox-tool-btn:disabled {
  opacity: 0.3;
  cursor: not-allowed;
}

.pdf-lightbox-zoom-reset {
  font-size: 0.82rem;
  font-family: inherit;
  font-variant-numeric: tabular-nums;
  padding: 0 0.55rem;
  min-width: 3.2rem;
  color: #334155;
  font-weight: 700;
}

.pdf-lightbox-zoom-reset.is-zoomed {
  color: #1d4ed8;
  background: #eff6ff;
  border-radius: 999px;
}

.pdf-lightbox-pan-btn {
  display: none;
  font-size: 1.1rem;
}

.pdf-lightbox.is-zoomed .pdf-lightbox-pan-btn {
  display: inline-flex;
}

.pdf-lightbox-counter {
  margin: 0;
  font-size: 0.88rem;
  font-weight: 800;
  color: var(--text);
  text-align: center;
  white-space: nowrap;
}

.pdf-lightbox-hint {
  margin: 0;
  font-size: 0.74rem;
  font-weight: 700;
  color: var(--muted);
  text-align: center;
}

.pdf-lightbox-hint[hidden] {
  display: none;
}

.pdf-lightbox-stage {
  position: relative;
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: stretch;
  gap: 0.35rem;
  min-height: 0;
}

.pdf-lightbox.is-zoomed .pdf-lightbox-stage {
  grid-template-columns: 1fr !important;
}

.pdf-lightbox.is-zoomed .pdf-lightbox-zone {
  display: none !important;
}

.pdf-lightbox-zone {
  appearance: none;
  width: 2.25rem;
  border: 1px solid #e2e8f0;
  border-radius: 0.65rem;
  background: #f8fafc;
  color: #1d4ed8;
  font-size: 1.35rem;
  font-weight: 900;
  cursor: pointer;
  transition: all 0.2s ease;
  display: flex;
  align-items: center;
  justify-content: center;
}

.pdf-lightbox-zone-prev::after {
  content: "→";
}

.pdf-lightbox-zone-next::after {
  content: "←";
}

.pdf-lightbox-zone:hover:not(:disabled) {
  background: #eff6ff;
  border-color: #bfdbfe;
  color: #2563eb;
}

.pdf-lightbox-zone:disabled {
  opacity: 0.25;
  cursor: not-allowed;
}

.pdf-lightbox-close {
  position: absolute;
  top: 0.65rem;
  inset-inline-end: 0.65rem;
  z-index: 2;
  appearance: none;
  border: 1px solid #bfdbfe;
  width: 2rem;
  height: 2rem;
  border-radius: 999px;
  background: #eff6ff;
  color: #1d4ed8;
  font-size: 0.95rem;
  font-weight: 800;
  cursor: pointer;
}

.pdf-lightbox-label {
  margin: 0;
  padding-inline-end: 2.5rem;
  font-size: 0.88rem;
  font-weight: 800;
  color: var(--muted);
  text-align: center;
}

.pdf-lightbox-canvas {
  overflow: hidden;
  max-height: calc(94vh - 7.5rem);
  height: min(78vh, 850px);
  display: flex;
  justify-content: center;
  align-items: center;
  min-width: 0;
  background: #f8fafc;
  border-radius: 12px;
  border: 1px solid var(--border);
  touch-action: none;
  user-select: none;
  -webkit-user-select: none;
}

.pdf-lightbox-canvas .pdf-pinch-viewport {
  position: relative;
  width: 100%;
  height: 100%;
  max-height: none;
  display: flex;
  align-items: center;
  justify-content: center;
  overflow: hidden;
  touch-action: none;
  user-select: none;
  -webkit-user-select: none;
  cursor: default;
}

.pdf-lightbox-canvas .pdf-pinch-viewport.is-zoomed {
  cursor: grab;
}

.pdf-pinch-inner {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  transform-origin: center center;
  will-change: transform;
  touch-action: none;
  user-select: none;
  -webkit-user-select: none;
}

.pdf-lightbox-canvas canvas {
  display: block;
  max-width: 100%;
  max-height: 100%;
  width: auto;
  height: auto;
  object-fit: contain;
  border-radius: 0.45rem;
  box-shadow: 0 8px 32px rgba(15, 23, 42, 0.15);
  pointer-events: auto;
  touch-action: none;
}

.video-player-shell {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.85rem;
}

.video-wrap {
  position: relative;
  width: 100%;
  aspect-ratio: 16 / 9;
  border-radius: var(--radius);
  overflow: hidden;
  border: 1px solid rgba(15, 23, 42, 0.2);
  background: #0f172a;
  box-shadow: 0 12px 32px rgba(15, 23, 42, 0.2);
}

.video-stage {
  position: absolute;
  inset: 0;
}

.video-controls-bar {
  display: flex;
  justify-content: center;
  width: 100%;
}

.video-controls-pill {
  display: inline-flex;
  align-items: center;
  gap: 0.55rem;
  padding: 0.5rem 0.6rem;
  border-radius: 999px;
  border: 1px solid rgba(124, 58, 237, 0.18);
  background: linear-gradient(180deg, rgba(255, 255, 255, 0.98), rgba(245, 243, 255, 0.96));
  box-shadow:
    0 10px 28px rgba(124, 58, 237, 0.12),
    inset 0 1px 0 rgba(255, 255, 255, 0.9);
  transition:
    transform 0.22s ease,
    box-shadow 0.22s ease,
    border-color 0.22s ease;
}

.video-player-shell:hover .video-controls-pill,
.video-player-shell:focus-within .video-controls-pill {
  border-color: rgba(124, 58, 237, 0.28);
  box-shadow:
    0 14px 34px rgba(124, 58, 237, 0.16),
    inset 0 1px 0 rgba(255, 255, 255, 0.95);
}

.video-controls-divider {
  width: 1px;
  align-self: stretch;
  margin: 0.15rem 0;
  background: linear-gradient(
    180deg,
    rgba(124, 58, 237, 0) 0%,
    rgba(124, 58, 237, 0.22) 50%,
    rgba(124, 58, 237, 0) 100%
  );
}

.btn-video-ctrl {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.65rem;
  min-width: 6.5rem;
  min-height: 3.2rem;
  padding: 0.5rem 0.95rem;
  border: 1px solid rgba(124, 58, 237, 0.14);
  border-radius: 999px;
  background: linear-gradient(180deg, rgba(124, 58, 237, 0.08), rgba(124, 58, 237, 0.03));
  color: #5b21b6;
  font-family: inherit;
  cursor: pointer;
  transition:
    transform 0.18s ease,
    background 0.18s ease,
    border-color 0.18s ease,
    box-shadow 0.18s ease;
}

.btn-video-ctrl-icon {
  display: grid;
  place-items: center;
  width: 2.15rem;
  height: 2.15rem;
  border-radius: 999px;
  background: rgba(124, 58, 237, 0.1);
  box-shadow: inset 0 0 0 1px rgba(124, 58, 237, 0.12);
  font-size: 1.15rem;
  line-height: 1;
}

.btn-video-ctrl-text {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 0.08rem;
  min-width: 2.5rem;
}

.btn-video-ctrl-label {
  font-size: 0.98rem;
  font-weight: 800;
  line-height: 1.1;
}

.btn-video-ctrl-hint {
  font-size: 0.68rem;
  font-weight: 700;
  line-height: 1;
  color: rgba(91, 33, 182, 0.72);
}

.btn-video-ctrl--rewind .btn-video-ctrl-icon {
  background: linear-gradient(135deg, rgba(14, 165, 233, 0.16), rgba(59, 130, 246, 0.1));
}

.btn-video-ctrl--forward .btn-video-ctrl-icon {
  background: linear-gradient(135deg, rgba(16, 185, 129, 0.16), rgba(5, 150, 105, 0.1));
}

.btn-video-ctrl--speed .btn-video-ctrl-icon {
  background: linear-gradient(135deg, rgba(167, 139, 250, 0.22), rgba(124, 58, 237, 0.12));
}

.btn-video-ctrl:hover {
  transform: translateY(-1px);
  background: linear-gradient(180deg, rgba(124, 58, 237, 0.12), rgba(124, 58, 237, 0.06));
  border-color: rgba(124, 58, 237, 0.24);
  box-shadow: 0 8px 20px rgba(124, 58, 237, 0.12);
}

.btn-video-ctrl:active {
  transform: translateY(0) scale(0.98);
}

.btn-video-ctrl:focus-visible {
  outline: 2px solid rgba(167, 139, 250, 0.85);
  outline-offset: 2px;
}

.btn-video-ctrl:disabled,
.btn-video-ctrl.is-disabled {
  opacity: 0.45;
  cursor: not-allowed;
  transform: none;
  box-shadow: none;
}

@media (max-width: 640px) {
  .video-controls-pill {
    gap: 0.4rem;
    padding: 0.45rem;
  }

  .btn-video-ctrl {
    min-width: 0;
    min-height: 3rem;
    padding: 0.45rem 0.7rem;
    gap: 0.5rem;
  }

  .btn-video-ctrl-hint {
    display: none;
  }

  .btn-video-ctrl-text {
    min-width: 0;
  }
}

.video-wrap iframe {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  border: none;
}

.video-player-host {
  position: absolute;
  inset: 0;
  z-index: 1;
  width: 100%;
  height: 100%;
}

.video-player-host iframe {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  border: none;
}

.video-caption {
  margin: 0.75rem 0 0;
  font-size: 0.88rem;
  color: var(--muted);
  font-weight: 600;
}

.exercise-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 0.95rem;
}

.exercise-item {
  padding: 1.1rem 1.15rem;
  border-radius: var(--radius);
  background: #fff;
  border: 1px solid rgba(79, 70, 229, 0.14);
  transition: border-color 0.22s ease, box-shadow 0.22s ease;
}

.exercise-item:hover {
  border-color: rgba(79, 70, 229, 0.22);
  box-shadow: var(--shadow-sm);
}

.exercise-item.exam-item {
  border-inline-start: 4px solid var(--violet);
  background: #fff;
}

.exercise-item-head {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.45rem 0.65rem;
  margin-bottom: 0.65rem;
  padding-bottom: 0.55rem;
  border-bottom: 1px dashed rgba(79, 70, 229, 0.18);
}

.exercise-label {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  padding: 0.28rem 0.65rem 0.28rem 0.5rem;
  border-radius: 999px;
  background: linear-gradient(135deg, rgba(79, 70, 229, 0.12), rgba(124, 58, 237, 0.08));
  border: 1px solid rgba(79, 70, 229, 0.22);
  color: var(--accent);
  font-weight: 800;
  line-height: 1.2;
  flex-shrink: 0;
}

.exercise-label-kicker {
  font-size: 0.72rem;
  font-weight: 700;
  opacity: 0.88;
}

.exercise-label-num {
  font-size: 0.88rem;
  letter-spacing: 0.02em;
  direction: ltr;
  unicode-bidi: isolate;
}

.exercise-item--book .exercise-label {
  background: linear-gradient(135deg, rgba(14, 165, 233, 0.14), rgba(56, 189, 248, 0.08));
  border-color: rgba(14, 165, 233, 0.28);
  color: #0369a1;
}

.exercise-item--extra .exercise-label {
  background: linear-gradient(135deg, rgba(79, 70, 229, 0.14), rgba(124, 58, 237, 0.08));
  border-color: rgba(79, 70, 229, 0.25);
  color: var(--accent);
}

.exercise-item--past .exercise-label,
.exercise-item.exam-item .exercise-label {
  background: linear-gradient(135deg, rgba(124, 58, 237, 0.14), rgba(167, 139, 250, 0.1));
  border-color: rgba(124, 58, 237, 0.28);
  color: #6d28d9;
}

.exercise-q {
  margin: 0 0 0.8rem;
  font-weight: 600;
  color: var(--text);
  line-height: 1.7;
}

.exercise-q.rich-content p {
  margin: 0;
  font-weight: inherit;
}

.exercise-year {
  display: inline-block;
  margin-inline-end: 0.4rem;
  padding: 0.2rem 0.55rem;
  border-radius: 999px;
  background: linear-gradient(135deg, var(--accent-soft), rgba(124, 58, 237, 0.1));
  color: var(--accent);
  font-size: 0.78rem;
  font-weight: 800;
}

.exercise-actions {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.5rem;
}

.btn-solution {
  appearance: none;
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 0.48rem 1rem;
  font: inherit;
  font-weight: 700;
  font-size: 0.88rem;
  cursor: pointer;
  background: var(--surface-solid);
  color: var(--accent);
  transition: background 0.22s ease, color 0.22s ease, transform 0.22s ease, box-shadow 0.22s ease;
}

.btn-solution:hover {
  background: var(--accent-soft);
  transform: translateY(-1px);
}

.btn-solution[aria-expanded="true"] {
  background: linear-gradient(135deg, var(--accent), var(--violet));
  color: #fff;
  border-color: transparent;
  box-shadow: 0 4px 14px var(--accent-glow);
}

.btn-solution-full {
  appearance: none;
  border: 1px solid rgba(16, 185, 129, 0.35);
  border-radius: 999px;
  padding: 0.48rem 1rem;
  font: inherit;
  font-weight: 700;
  font-size: 0.88rem;
  cursor: pointer;
  background: rgba(255, 255, 255, 0.92);
  color: #047857;
  transition: background 0.22s ease, color 0.22s ease, transform 0.22s ease, box-shadow 0.22s ease;
}

.btn-solution-full:hover {
  background: rgba(16, 185, 129, 0.12);
  transform: translateY(-1px);
}

.btn-solution-full.hidden {
  display: none;
}

.btn-solution-next {
  appearance: none;
  border: 1px solid rgba(16, 185, 129, 0.35);
  border-radius: 999px;
  padding: 0.48rem 1rem;
  font: inherit;
  font-weight: 700;
  font-size: 0.88rem;
  cursor: pointer;
  background: rgba(255, 255, 255, 0.92);
  color: #047857;
  transition: background 0.22s ease, color 0.22s ease, transform 0.22s ease, box-shadow 0.22s ease;
}

.btn-solution-next:hover {
  background: rgba(16, 185, 129, 0.12);
  transform: translateY(-1px);
}

.btn-solution-next.hidden {
  display: none;
}

.exercise-solution table.solution-steps th:nth-child(4),
.exercise-solution table.solution-steps td:nth-child(4) {
  display: none;
}

.exercise-solution {
  display: none;
  margin: 0.85rem 0 0;
  padding: 0.95rem 1.05rem;
  border-radius: 0.8rem;
  background: linear-gradient(135deg, rgba(16, 185, 129, 0.1), rgba(52, 211, 153, 0.06));
  border: 1px solid rgba(16, 185, 129, 0.22);
  color: #065f46;
  font-weight: 600;
  line-height: 1.7;
  max-width: 100%;
  min-width: 0;
  box-sizing: border-box;
}

.exercise-solution.open {
  display: block;
  animation: fadeUp 0.35s ease both;
  overflow-x: hidden;
}

.rich-content table.solution-steps {
  width: 100%;
  border-collapse: separate;
  border-spacing: 0;
  margin: 0;
  font-size: 0.92rem;
  font-weight: 500;
  direction: rtl;
}

.rich-content table.solution-steps th:first-child,
.rich-content table.solution-steps td:first-child {
  text-align: center;
  min-width: 1.65rem;
  width: 1.75rem;
  max-width: 2rem;
  padding: 0.35rem 0.15rem;
  font-size: 0.7rem;
  font-weight: 600;
  line-height: 1.15;
}

.rich-content table.solution-steps th:first-child {
  font-size: 0.62rem;
  font-weight: 700;
  letter-spacing: 0;
}

.rich-content table.solution-steps th,
.rich-content table.solution-steps td {
  padding: 0.55rem 0.7rem;
  border: 1px solid rgba(16, 185, 129, 0.28);
  text-align: start;
  vertical-align: middle;
}

.rich-content table.solution-steps th {
  background: rgba(16, 185, 129, 0.14);
  font-weight: 800;
  color: #047857;
}

.rich-content table.solution-steps tr.step-hidden {
  display: none;
}

.rich-content table.solution-steps tr.step-visible {
  animation: fadeUp 0.3s ease both;
}

.rich-content .table-scroll-wrap {
  width: 100%;
  max-width: 100%;
  box-sizing: border-box;
}

.table-scroll-wrap.scroll-axis-dragging {
  user-select: none;
  cursor: grabbing;
}

@media (max-width: 900px) {
  .exercise-item {
    min-width: 0;
    max-width: 100%;
    overflow-x: hidden;
    box-sizing: border-box;
  }

  .exercise-solution,
  .exercise-solution.open {
    padding: 0.65rem 0.7rem;
    overflow-x: hidden;
    max-width: 100%;
  }

  .rich-content .table-scroll-wrap {
    display: block;
    width: 100%;
    max-width: 100%;
    overflow-x: auto;
    overflow-y: hidden;
    -webkit-overflow-scrolling: touch;
    overscroll-behavior-x: contain;
    touch-action: pan-x pan-y;
    scrollbar-width: thin;
  }

  .rich-content table.solution-steps {
    width: max-content;
    min-width: 0;
    max-width: none;
    font-size: 0.88rem;
  }

  .rich-content table.solution-steps th:first-child,
  .rich-content table.solution-steps td:first-child {
    position: static;
    box-shadow: none;
    min-width: 1.5rem;
    width: 1.65rem;
    max-width: 1.85rem;
    text-align: center;
    vertical-align: middle;
    padding: 0.3rem 0.12rem;
    font-size: 0.66rem;
  }

  .rich-content table.solution-steps th:first-child {
    white-space: nowrap;
    line-height: 1.1;
    font-size: 0.58rem;
    padding-inline: 0.12rem;
  }

  .rich-content table.solution-steps td:first-child {
    font-weight: 600;
    font-size: 0.68rem;
  }

  .rich-content table.solution-steps th,
  .rich-content table.solution-steps td {
    white-space: nowrap;
  }

  .rich-content table.solution-steps th:nth-child(3),
  .rich-content table.solution-steps td:nth-child(3) {
    white-space: normal;
    min-width: 9rem;
    max-width: 14rem;
  }

  .rich-content table.solution-steps th:nth-child(2),
  .rich-content table.solution-steps td:nth-child(2) {
    min-width: 8rem;
  }

  .rich-content table.solution-steps th:nth-child(4),
  .rich-content table.solution-steps td:nth-child(4) {
    min-width: 4.75rem;
  }

  .rich-content table.solution-steps mjx-container {
    max-width: none;
  }

  .rich-content table.md-table {
    width: max-content;
    min-width: 100%;
    max-width: none;
    font-size: 0.88rem;
    table-layout: auto;
  }

  .rich-content table.md-table th,
  .rich-content table.md-table td {
    vertical-align: top;
  }

  .rich-content table.md-table th:first-child,
  .rich-content table.md-table td:first-child {
    white-space: nowrap;
  }
}

.btn-reveal-step {
  appearance: none;
  border: 1px solid rgba(16, 185, 129, 0.35);
  border-radius: 999px;
  padding: 0.35rem 0.85rem;
  font: inherit;
  font-weight: 700;
  font-size: 0.82rem;
  cursor: pointer;
  background: rgba(255, 255, 255, 0.92);
  color: #047857;
  white-space: nowrap;
  transition: background 0.2s ease, transform 0.2s ease, box-shadow 0.2s ease;
}

.btn-reveal-step:hover {
  background: rgba(16, 185, 129, 0.12);
  transform: translateY(-1px);
}

.comments-form {
  display: grid;
  gap: 0.7rem;
  margin-bottom: 1.25rem;
  padding: 1rem;
  border-radius: var(--radius);
  background: rgba(238, 242, 255, 0.45);
  border: 1px dashed var(--border);
}

.comments-form input,
.comments-form textarea {
  width: 100%;
  padding: 0.78rem 0.95rem;
  border: 1px solid var(--border);
  border-radius: 0.85rem;
  font: inherit;
  background: rgba(255, 255, 255, 0.95);
  transition: border-color 0.2s ease, box-shadow 0.2s ease;
}

.comments-form input:focus,
.comments-form textarea:focus {
  outline: none;
  border-color: var(--accent-light);
  box-shadow: 0 0 0 3px var(--accent-soft);
}

.comments-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 0.7rem;
}

.comment-item {
  padding: 1rem 1.05rem;
  border-radius: 0.9rem;
  background: linear-gradient(160deg, rgba(255, 255, 255, 0.95), var(--accent-soft));
  border: 1px solid var(--border);
  transition: transform 0.2s ease;
}

.comment-item:hover {
  transform: translateX(-2px);
}

.comment-meta {
  display: flex;
  justify-content: space-between;
  gap: 0.5rem;
  margin-bottom: 0.4rem;
  font-size: 0.82rem;
  color: var(--muted);
}

.comment-author {
  font-weight: 800;
  color: var(--accent);
}

.comment-body {
  margin: 0;
  color: var(--text);
  line-height: 1.65;
}

.comments-empty {
  margin: 0;
  color: var(--muted);
  font-size: 0.95rem;
  text-align: center;
  padding: 1rem;
}

.lesson-toc {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-bottom: 0.5rem;
  padding: 0.85rem 1rem;
  border-radius: var(--radius-lg);
  background: rgba(255, 255, 255, 0.88);
  border: 1px solid var(--border);
  box-shadow: var(--shadow-sm);
  position: sticky;
  top: calc(var(--topbar-height) + 0.65rem);
  z-index: 5;
  backdrop-filter: blur(12px);
}

.lesson-toc a {
  padding: 0.42rem 0.85rem;
  border-radius: 999px;
  background: var(--accent-soft);
  color: var(--accent);
  text-decoration: none;
  font-size: 0.84rem;
  font-weight: 700;
  border: 1px solid transparent;
  transition: background 0.2s ease, color 0.2s ease, transform 0.2s ease, box-shadow 0.2s ease;
}

.lesson-toc a:hover {
  background: linear-gradient(135deg, var(--accent), var(--violet));
  color: #fff;
  transform: translateY(-1px);
  box-shadow: 0 4px 12px var(--accent-glow);
}

@media (max-width: 768px) {
  .lesson-content {
    max-width: none;
  }

  .lesson-toc {
    position: static;
    flex-wrap: nowrap;
    overflow-x: auto;
    overscroll-behavior-x: contain;
    -webkit-overflow-scrolling: touch;
    scrollbar-width: none;
    gap: 0.4rem;
    padding: 0.65rem 0.75rem;
    margin-inline: -0.15rem;
  }

  .lesson-toc::-webkit-scrollbar {
    display: none;
  }

  .lesson-toc a {
    flex-shrink: 0;
    font-size: 0.8rem;
    padding: 0.38rem 0.72rem;
  }

  .lesson-block {
    padding: 1.05rem 0.95rem;
    border-radius: var(--radius);
  }

  .lesson-block-title {
    font-size: 1.05rem;
    gap: 0.5rem;
  }

  .lesson-block-icon {
    width: 2rem;
    height: 2rem;
    font-size: 0.95rem;
    flex-shrink: 0;
  }

  .exercise-item {
    padding: 0.95rem;
  }

  .exercise-q {
    font-size: 0.95rem;
  }

  .btn-solution {
    width: 100%;
    text-align: center;
    padding: 0.55rem 1rem;
  }

  .comment-meta {
    flex-direction: column;
    align-items: flex-start;
    gap: 0.2rem;
  }

  .pdf-scroll {
    padding: 0.35rem 0;
    max-height: none;
  }

  .pdf-page {
    padding: 0.35rem 0.45rem 0.45rem;
    width: 100% !important;
  }

  .pdf-page-canvas-wrap,
  .pdf-page canvas {
    width: 100% !important;
    max-width: 100% !important;
    max-height: none !important;
    height: auto !important;
  }

  .pdf-lightbox {
    padding: 0;
  }

  .pdf-lightbox-panel {
    width: 100vw;
    height: 100dvh;
    max-height: 100dvh;
    border-radius: 0;
    padding: max(0.5rem, env(safe-area-inset-top)) max(0.5rem, env(safe-area-inset-right))
      max(0.5rem, env(safe-area-inset-bottom)) max(0.5rem, env(safe-area-inset-left));
  }

  .pdf-lightbox-toolbar {
    padding-inline-end: 2.2rem;
    gap: 0.4rem;
  }

  .pdf-lightbox-hint {
    font-size: 0.7rem;
  }

  .pdf-lightbox-stage {
    grid-template-columns: 1fr;
    flex: 1;
    min-height: 0;
  }

  .pdf-lightbox-zone {
    display: none;
  }

  .pdf-lightbox-canvas {
    height: calc(100dvh - 8rem);
    max-height: calc(100dvh - 8rem);
    border-radius: 8px;
  }

  .pdf-wrap iframe,
  .pdf-wrap-single iframe {
    height: min(78vh, 720px);
  }

  .explanation-step-title {
    padding: 1rem 1rem 0.75rem;
    font-size: 1.02rem;
    gap: 0.65rem;
  }

  .explanation-step-title::before {
    width: 1.9rem;
    height: 1.9rem;
    font-size: 0.85rem;
  }

  .explanation-step-body {
    padding: 0 1rem 0.25rem;
  }

  .explanation-step-actions {
    margin: 0.75rem 1rem 1.1rem;
  }

  .btn-reveal-explanation {
    width: 100%;
    justify-content: center;
  }

  .comprehension-check-question,
  .comprehension-check-answer {
    margin-inline: 0.75rem;
    padding: 0.5rem 0.65rem;
  }

  .comprehension-check-actions {
    padding-inline: 0.75rem;
    padding-bottom: 0.65rem;
  }

  .comprehension-check-next-wrap {
    padding-inline: 0.75rem;
    padding-bottom: 0.75rem;
  }

  .btn-check-reveal,
  .btn-check-next {
    width: 100%;
    flex: 1 1 auto;
    justify-content: center;
  }
}

/* ===== Lesson image lightbox (explanation & exercises) ===== */
body.lesson-image-lightbox-open {
  overflow: hidden;
}

.lesson-image-lightbox {
  padding: 0;
  border: none;
  margin: 0;
  max-width: none;
  width: 100%;
  height: 100%;
  max-height: none;
  background: transparent;
  overflow: visible;
}

.lesson-image-lightbox[open] {
  display: flex;
  align-items: center;
  justify-content: center;
  position: fixed;
  inset: 0;
  width: 100%;
  height: 100%;
  padding: max(1rem, env(safe-area-inset-top)) max(1rem, env(safe-area-inset-right))
    max(1rem, env(safe-area-inset-bottom)) max(1rem, env(safe-area-inset-left));
}

.lesson-image-lightbox::backdrop {
  background: rgba(15, 23, 42, 0.88);
}

.lesson-image-lightbox-inner {
  position: relative;
  width: min(96vw, 1020px);
  max-height: min(94vh, 920px);
  margin: auto;
  background: #fff;
  border-radius: 16px;
  overflow: hidden;
  padding: 0.75rem;
  box-shadow: 0 24px 64px rgba(15, 23, 42, 0.45);
  display: flex;
  flex-direction: column;
}

.lesson-image-lightbox-figure {
  margin: 0;
  display: flex;
  flex-direction: column;
  height: 100%;
  min-height: 0;
}

.lesson-image-lightbox-stage {
  position: relative;
  width: 100%;
  height: min(76vh, 720px);
  overflow: hidden;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #f8fafc;
  border: 1px solid #e2e8f0;
  border-radius: 12px;
  touch-action: none;
  user-select: none;
  -webkit-user-select: none;
}

.lesson-image-lightbox-img {
  display: block;
  max-width: 100%;
  max-height: 100%;
  width: auto;
  height: auto;
  object-fit: contain;
  transform-origin: center center;
  will-change: transform;
  touch-action: none;
  user-select: none;
  -webkit-user-drag: none;
  pointer-events: auto;
}

.lesson-image-lightbox-toolbar {
  position: absolute;
  top: 1rem;
  left: 50%;
  transform: translateX(-50%);
  z-index: 4;
  display: inline-flex;
  align-items: center;
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  border: 1px solid rgba(203, 213, 225, 0.9);
  border-radius: 999px;
  padding: 2px 4px;
  box-shadow: 0 4px 16px rgba(15, 23, 42, 0.14);
  gap: 3px;
  direction: ltr;
}

.lesson-image-lightbox-tool-btn {
  border: none;
  background: transparent;
  color: #4338ca;
  font-size: 1.15rem;
  font-weight: 700;
  height: 2rem;
  min-width: 2rem;
  padding: 0 0.4rem;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: 999px;
  cursor: pointer;
  line-height: 1;
  transition: background 0.15s ease, color 0.15s ease, transform 0.1s ease;
}

.lesson-image-lightbox-tool-btn:hover:not(:disabled) {
  background: rgba(79, 70, 229, 0.1);
  color: #3730a3;
}

.lesson-image-lightbox-tool-btn:active:not(:disabled) {
  transform: scale(0.92);
}

.lesson-image-lightbox-tool-btn:disabled {
  opacity: 0.3;
  cursor: not-allowed;
}

.lesson-image-lightbox-zoom-reset {
  font-size: 0.82rem;
  font-family: inherit;
  font-variant-numeric: tabular-nums;
  padding: 0 0.55rem;
  min-width: 3.2rem;
  color: #334155;
  font-weight: 600;
}

.lesson-image-lightbox-zoom-reset.is-zoomed {
  color: #4338ca;
  background: rgba(79, 70, 229, 0.12);
}

.lesson-image-lightbox-caption-wrap {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 0.75rem;
  padding: 0.65rem 0.35rem 0.25rem;
  color: #64748b;
  font-size: 0.92rem;
}

.lesson-image-lightbox-caption[hidden] {
  display: none;
}

.lesson-image-lightbox-counter {
  font-variant-numeric: tabular-nums;
  font-size: 0.82rem;
}

.lesson-image-lightbox-close {
  position: absolute;
  top: 1rem;
  right: 1rem;
  left: auto;
  z-index: 5;
  width: 2.35rem;
  height: 2.35rem;
  border: 1px solid rgba(203, 213, 225, 0.8);
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  color: #4f46e5;
  font-size: 1.35rem;
  line-height: 1;
  cursor: pointer;
  box-shadow: 0 2px 12px rgba(15, 23, 42, 0.12);
  display: grid;
  place-items: center;
}

.lesson-image-lightbox-close:hover {
  background: #fff;
  color: #3730a3;
  transform: scale(1.05);
}

.lesson-image-lightbox-nav {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
  z-index: 3;
  width: 2.35rem;
  height: 2.35rem;
  border: 1px solid rgba(203, 213, 225, 0.8);
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  color: #4f46e5;
  font-size: 0;
  line-height: 1;
  cursor: pointer;
  box-shadow: 0 2px 10px rgba(15, 23, 42, 0.12);
  display: grid;
  place-items: center;
  direction: ltr;
  unicode-bidi: isolate;
}

.lesson-image-lightbox-nav::before {
  content: "";
  display: block;
  width: 0.45rem;
  height: 0.45rem;
  border: solid currentColor;
  border-width: 0 2.5px 2.5px 0;
  box-sizing: border-box;
}

.lesson-image-lightbox-prev::before {
  transform: rotate(135deg);
}

.lesson-image-lightbox-next::before {
  transform: rotate(-45deg);
}

.lesson-image-lightbox-nav:disabled {
  opacity: 0.35;
  cursor: not-allowed;
}

.lesson-image-lightbox-prev {
  left: 1rem;
  right: auto;
}

.lesson-image-lightbox-next {
  right: 1rem;
  left: auto;
}

html[dir="rtl"] .lesson-image-lightbox-prev {
  left: auto;
  right: 1rem;
}

html[dir="rtl"] .lesson-image-lightbox-next {
  right: auto;
  left: 1rem;
}

html[dir="rtl"] .lesson-image-lightbox-prev::before {
  transform: rotate(-45deg);
}

html[dir="rtl"] .lesson-image-lightbox-next::before {
  transform: rotate(135deg);
}

@media (max-width: 680px) {
  .lesson-image-lightbox[open] {
    padding: 0;
  }

  .lesson-image-lightbox-inner {
    width: 100vw;
    height: 100dvh;
    max-height: 100dvh;
    border-radius: 0;
    padding: max(0.5rem, env(safe-area-inset-top)) max(0.5rem, env(safe-area-inset-right))
      max(0.5rem, env(safe-area-inset-bottom)) max(0.5rem, env(safe-area-inset-left));
  }

  .lesson-image-lightbox-stage {
    height: calc(100dvh - 5.5rem);
    border-radius: 8px;
  }

  .lesson-image-lightbox-toolbar {
    top: auto;
    bottom: 2.85rem;
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.2);
  }
}