/* ==========================================================================
   BÀI 7: ĐỘT BIẾN NHIỄM SẮC THỂ - SINH HỌC 12 (KẾT NỐI TRI THỨC)
   PHONG CÁCH: BÁO IN / TÀI LIỆU HỌC THUẬT TỐI GIẢN (LAYOUT THONGNGUYENN)
   MỤC ĐÍCH: HỌC SINH TRÌNH CHIẾU TRÊN LỚP (18 SLIDE)
   ========================================================================== */

/* 1. CSS VARIABLES */
:root {
  --bg: #ffffff;
  --text: #1a1a1a;
  --text-muted: #64748b;
  --border: #e2e8f0;
  --border-strong: #1e293b;
  --primary: #0891b2;
  --primary-dark: #0e7490;
  --primary-light: #cffafe;
  --secondary: #7c3aed;
  --secondary-light: #ede9fe;
  --accent: #f59e0b;
  --accent-light: #fef3c7;
  --success: #10b981;
  --success-light: #d1fae5;
  --error: #ef4444;
  --error-light: #fee2e2;
  --highlight: #fef3c7;
  --table-head-bg: #0891b2;
  --table-head-text: #ffffff;
  --table-row-alt: #f8fafc;
  --bg-alt: #f8fafc;
  --gradient-1: linear-gradient(135deg, #0891b2 0%, #7c3aed 100%);
  --gradient-2: linear-gradient(135deg, #06b6d4 0%, #3b82f6 100%);
  --stagger-delay-0: 0.05s;
  --stagger-delay-1: 0.20s;
  --stagger-delay-2: 0.35s;
  --stagger-delay-3: 0.50s;
  --stagger-delay-4: 0.65s;
  --stagger-delay-5: 0.80s;
  --stagger-delay-6: 0.95s;
  --stagger-delay-7: 1.10s;
}

/* 2. RESET CƠ BẢN */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html, body {
  width: 100vw;
  height: 100vh;
  overflow: hidden;
  font-family: 'Be Vietnam Pro', 'Inter', 'Segoe UI', -apple-system, BlinkMacSystemFont, sans-serif;
  background-color: var(--bg);
  color: var(--text);
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
  font-feature-settings: "kern" 1, "liga" 1, "calt" 1;
  font-variant-ligatures: common-ligatures;
}

h1, h2, h3, p {
  font-feature-settings: "kern" 1, "liga" 1, "calt" 1;
  font-variant-ligatures: common-ligatures;
}

/* 3. THANH TIẾN ĐỘ TRÊN CÙNG */
.progress-bar-container {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 4px;
  background-color: transparent;
  z-index: 1000;
}

.progress-bar {
  height: 100%;
  width: 5.55%;
  background: var(--gradient-2);
  transition: width 0.3s cubic-bezier(0.2, 0.8, 0.2, 1);
}

/* 4. TOP BAR */
.top-bar {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 50px;
  background-color: var(--bg);
  border-bottom: 2px solid var(--border-strong);
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0 24px;
  z-index: 900;
  user-select: none;
}

.top-bar-left {
  display: flex;
  align-items: center;
}

.top-badge {
  font-size: 0.8rem;
  font-weight: 800;
  letter-spacing: 1px;
  background: var(--primary);
  color: var(--bg);
  padding: 4px 10px;
  border-radius: 2px;
  text-transform: uppercase;
}

.top-bar-center {
  font-size: 0.95rem;
  font-weight: 850;
  letter-spacing: 0.8px;
  text-transform: uppercase;
  color: var(--text);
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  max-width: 60%;
}

.top-bar-right {
  font-size: 0.95rem;
  font-weight: 850;
  font-family: monospace;
  letter-spacing: 1px;
}

/* 5. FOOTER CỐ ĐỊNH Ở ĐÁY */
.footer-bar {
  position: fixed;
  bottom: 0;
  left: 0;
  width: 100%;
  height: 48px;
  background-color: var(--bg);
  border-top: 1px solid var(--border);
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0 24px;
  z-index: 900;
  font-size: 0.88rem;
  user-select: none;
}

.lesson-tag {
  font-weight: 750;
  color: var(--text-muted);
}

.footer-center {
  display: flex;
  align-items: center;
  gap: 12px;
}

.nav-btn {
  background: var(--bg);
  color: var(--text);
  border: 1.5px solid var(--border-strong);
  padding: 5px 14px;
  border-radius: 3px;
  font-size: 0.85rem;
  font-weight: 800;
  cursor: pointer;
  transition: all 0.15s ease;
}

.nav-btn:hover {
  background: var(--primary-dark);
  border-color: var(--primary-dark);
  color: var(--bg);
}

.nav-counter {
  font-weight: 800;
  font-family: monospace;
  font-size: 0.95rem;
  min-width: 60px;
  text-align: center;
}

.footer-right {
  display: flex;
  align-items: center;
  gap: 10px;
}

.tool-icon-btn {
  background: var(--bg);
  color: var(--text);
  border: 1.5px solid var(--border-strong);
  padding: 4px 10px;
  border-radius: 3px;
  cursor: pointer;
  font-size: 0.85rem;
  font-weight: 800;
  transition: all 0.15s ease;
}

.tool-icon-btn:hover {
  background: var(--primary-dark);
  border-color: var(--primary-dark);
  color: var(--bg);
}

.group-info {
  font-weight: 700;
  color: var(--text-muted);
  margin-left: 6px;
  font-size: 0.85rem;
}

/* 6. KHUNG CHỨA TOÀN BỘ SLIDE (100vw x 100vh) */
.presentation-stage {
  position: relative;
  width: 100vw;
  height: 100vh;
  overflow: hidden;
}

/* 7. SLIDE CHÍNH */
.slide {
  position: absolute;
  inset: 0;
  width: 100vw;
  height: 100vh;
  padding: 60px 80px;
  background-color: var(--bg);
  overflow-y: auto;
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
  transition: opacity 0.3s ease, transform 0.3s cubic-bezier(0.2, 0.8, 0.2, 1);
  transform: translateX(40px);
  z-index: 10;
}

.slide.active {
  opacity: 1;
  visibility: visible;
  pointer-events: auto;
  transform: translateX(0);
  z-index: 20;
}

.slide.slide-prev-out {
  transform: translateX(-40px);
}

/* KHUNG VIỀN ĐEN 2PX BAO QUANH SLIDE */
.slide-inner {
  position: relative;
  width: 100%;
  max-width: 1260px;
  min-height: calc(100vh - 120px);
  margin: 0 auto;
  border: 2px solid var(--border-strong);
  padding: 35px 45px;
  background-color: var(--bg);
  border-radius: 4px;
  display: flex;
  flex-direction: column;
  justify-content: flex-start;
}

.slide-inner:not(.hero-inner):not(.end-inner)::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 60px;
  height: 6px;
  border-radius: 0 0 6px 0;
  background: var(--gradient-2);
}

.mini-game-intro > .chapter-badge {
  color: var(--accent);
}

.mini-game-intro .slide-inner {
  border-style: dashed;
  border-color: var(--accent);
}

.mini-game-grid {
  display: grid;
  grid-template-columns: 1.2fr 0.8fr;
  gap: 24px;
  align-items: start;
}

.mini-game-details {
  display: grid;
  gap: 14px;
}

.mini-game-intro .content-card {
  margin-bottom: 0;
}

.mini-game-intro .content-card.mini-game-rules {
  background: var(--accent-light);
  border-left-color: var(--accent);
}

.mini-game-intro .content-card.mini-game-objectives {
  background: var(--primary-light);
  border-left-color: var(--primary);
}

.mini-game-visual {
  display: flex;
  flex-direction: column;
}

.mini-game-image {
  min-height: 300px;
  margin: 0 0 14px;
}

.mini-game-intro .mini-game-hint {
  margin-top: 0;
  background: var(--success-light);
  border-color: var(--success);
  border-left-color: var(--success);
}

/* 8. CHAPTER BADGE (SỐ CHƯƠNG LỚN MỜ GÓC PHẢI) */
.chapter-badge {
  position: absolute;
  top: 50px;
  right: 70px;
  font-size: 10rem;
  font-weight: 900;
  color: var(--secondary);
  opacity: 0.12;
  line-height: 1;
  pointer-events: none;
  user-select: none;
  z-index: 1;
  font-family: inherit;
}

.chapter-badge::after {
  content: " 🧬";
  display: inline-block;
  font-size: 1.8rem;
  vertical-align: top;
  opacity: 0.9;
}

/* 9. TIÊU ĐỀ SLIDE */
.slide-title {
  font-size: 2.5rem;
  font-weight: 800;
  text-transform: UPPERCASE;
  border-bottom: 3px solid var(--primary);
  padding-bottom: 15px;
  margin-bottom: 24px;
  letter-spacing: 0;
  line-height: 1.25;
  color: var(--primary);
  position: relative;
  z-index: 2;
}

h3 {
  font-size: 1.25rem;
  font-weight: 800;
  text-transform: UPPERCASE;
  margin-bottom: 10px;
  letter-spacing: 0;
}

h4 {
  font-size: 1.05rem;
  font-weight: 800;
  margin-bottom: 6px;
}

p {
  font-size: 0.95rem;
  line-height: 1.6;
  color: var(--text);
}

/* 10. STAT BOX (SỐ LIỆU NỔI BẬT) */
.stat-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 16px;
  margin-top: 14px;
}

.stat {
  border: 2px solid var(--primary);
  padding: 20px;
  border-radius: 6px;
  background: var(--bg);
  display: flex;
  flex-direction: column;
  justify-content: center;
  transition: transform 0.2s ease;
}

.stat:hover {
  transform: translateY(-2px);
}

.stat-value {
  font-size: 3rem;
  font-weight: 800;
  color: var(--primary);
  line-height: 1.25;
  margin-bottom: 6px;
  letter-spacing: 0;
}

.stat-label {
  font-size: 0.85rem;
  text-transform: uppercase;
  font-weight: 750;
  color: var(--text-muted);
  letter-spacing: 0.5px;
}

/* 11. CONTENT CARD */
.content-card {
  background: var(--primary-light);
  border: 2px solid var(--border);
  border-left: 6px solid var(--primary);
  padding: 20px;
  border-radius: 6px;
  transition: transform 0.2s ease, box-shadow 0.2s ease;
  margin-bottom: 14px;
  position: relative;
  z-index: 2;
}

.content-card:hover {
  transform: translateX(4px);
  border-color: var(--primary);
  box-shadow: 2px 4px 12px rgba(8, 145, 178, 0.16);
}

.content-card:nth-of-type(even) {
  background: var(--secondary-light);
  border-left-color: var(--secondary);
}

.content-card:nth-of-type(even):hover {
  border-color: var(--primary);
}

.card-title {
  font-size: 0.95rem;
  font-weight: 700;
  text-transform: UPPERCASE;
  border-bottom: 1.5px solid var(--border-strong);
  padding-bottom: 6px;
  margin-bottom: 12px;
  letter-spacing: 0.3px;
}

.card-tag {
  font-size: 0.75rem;
  font-weight: 850;
  background: var(--secondary);
  color: var(--bg);
  display: inline-block;
  padding: 3px 7px;
  border-radius: 2px;
  margin-bottom: 8px;
}

/* 12. BẢNG BIỂU (TABLE) */
.table-container {
  width: 100%;
  margin: 12px 0 16px 0;
  border: 2px solid var(--primary);
  border-radius: 4px;
  overflow: hidden;
  background: var(--bg);
  position: relative;
  z-index: 2;
}

.academic-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.92rem;
  text-align: left;
}

.academic-table th {
  background-color: var(--table-head-bg);
  color: var(--table-head-text);
  padding: 12px 15px;
  font-weight: 700;
  text-transform: UPPERCASE;
  letter-spacing: 0.5px;
  border-right: 1px solid rgba(255, 255, 255, 0.2);
}

.academic-table td {
  padding: 12px 15px;
  border-bottom: 1px solid var(--border);
  border-right: 1px solid var(--border);
  vertical-align: top;
  line-height: 1.5;
}

.academic-table tbody tr:nth-child(even) {
  background-color: var(--table-row-alt);
}

.academic-table tbody tr:last-child td {
  border-bottom: none;
}

.ans-badge {
  background: var(--border-strong);
  color: var(--bg);
  font-weight: 900;
  padding: 3px 12px;
  border-radius: 3px;
  font-family: monospace;
}

/* 13. HIGHLIGHT BOX & NOTE BOX */
.highlight-box {
  background-color: var(--accent-light);
  border: 2px solid var(--border);
  border-left: 6px solid var(--accent);
  padding: 18px 22px;
  border-radius: 6px;
  margin-bottom: 16px;
  font-size: 0.95rem;
  line-height: 1.55;
  position: relative;
  z-index: 2;
}

.big-definition {
  font-size: 1.05rem;
  padding: 20px 24px;
}

.note-box {
  background-color: var(--primary-light);
  border: 1.5px solid var(--border);
  border-left: 6px solid var(--primary);
  padding: 14px 18px;
  border-radius: 4px;
  font-size: 0.9rem;
  margin-top: 14px;
  line-height: 1.55;
}

/* 14. HIGHLIGHT TEXT & KEYWORD */
.highlight-text {
  background: var(--accent-light);
  font-weight: 600;
  padding: 0 2px;
  border-radius: 2px;
}

.keyword {
  font-weight: 700;
  text-decoration: underline;
  text-decoration-thickness: 2px;
  text-underline-offset: 3px;
}

kbd {
  background-color: var(--bg-alt);
  border: 1px solid var(--border-strong);
  padding: 2px 6px;
  border-radius: 3px;
  font-family: inherit;
  font-size: 0.85rem;
  font-weight: 700;
}

/* ==========================================================================
   15. PLACEHOLDER HÌNH ẢNH (QUAN TRỌNG)
   ========================================================================== */
.image-placeholder {
  width: 100%;
  min-height: 280px;
  border: 2px dashed var(--primary);
  border-radius: 12px;
  margin: 20px 0;
  background: #f8fafc;
  display: flex;
  align-items: center;
  justify-content: center;
  overflow: hidden;
  position: relative;
}

.image-placeholder img {
  width: 100%;
  height: 100%;
  object-fit: contain;
  display: block;
}

.image-fallback {
  display: none;
  flex-direction: column;
  align-items: center;
  gap: 10px;
  color: var(--text-muted);
  text-align: center;
  padding: 20px;
}

.image-icon {
  font-size: 3rem;
}

.image-text {
  font-size: 1.1rem;
  font-weight: 600;
  color: var(--primary);
}

.image-hint {
  font-size: 0.85rem;
  color: #9ca3af;
  font-style: italic;
}

/* 16. BỐ CỤC CHIA CỘT SLIDE */
.slide-split {
  display: grid;
  grid-template-columns: 1.25fr 0.75fr;
  gap: 24px;
  align-items: start;
}

.two-columns-simple {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
}

/* DANH SÁCH */
.bullet-list {
  list-style: none;
  margin-top: 6px;
}

.bullet-list > li {
  position: relative;
  padding-left: 18px;
  margin-bottom: 8px;
  font-size: 0.92rem;
}

.bullet-list > li::before {
  content: "■";
  position: absolute;
  left: 0;
  top: 2px;
  font-size: 0.68rem;
  color: var(--text);
}

.bullet-list ul {
  margin: 6px 0 6px 16px;
  list-style-type: circle;
}

.bullet-list ul li {
  margin-bottom: 4px;
}

.clean-list {
  list-style: none;
}

.clean-list li {
  margin-bottom: 8px;
  font-size: 0.92rem;
}

/* 17. TRANG BÌA (HERO) */
.hero-inner {
  justify-content: center;
  padding: 40px 50px;
}

#slide-1 .hero-inner {
  overflow: hidden;
  border: 0;
  border-radius: 14px;
  background: var(--gradient-1);
  color: #ffffff;
  box-shadow: 0 18px 48px rgba(14, 116, 144, 0.22);
}

#slide-1 .hero-inner > :not(.dna-decoration) {
  position: relative;
  z-index: 1;
}

#slide-1 .dna-decoration {
  position: absolute;
  z-index: 0;
  width: 300px;
  height: 520px;
  right: 3%;
  top: 50%;
  transform: translateY(-50%);
  opacity: 0.16;
  pointer-events: none;
}

#slide-1 .hero-title,
#slide-1 .hero-subtitle,
#slide-1 .hero-footer-note,
#slide-1 .hero-footer-note p,
#slide-1 .hero-inner .stat-value,
#slide-1 .hero-inner .stat-label,
#slide-1 .hero-inner .clean-list,
#slide-1 .hero-inner .card-title {
  color: #ffffff;
}

#slide-1 .info-card,
#slide-1 .stat {
  background: rgba(255, 255, 255, 0.14);
  border-color: rgba(255, 255, 255, 0.6);
}

#slide-1 .info-card {
  border-left-color: rgba(255, 255, 255, 0.85);
}

#slide-1 .hero-subtitle,
#slide-1 .hero-footer-note {
  border-color: rgba(255, 255, 255, 0.45);
}

.hero-top {
  margin-bottom: 14px;
}

.hero-badge {
  background: rgba(255, 255, 255, 0.18);
  color: var(--bg);
  font-size: 0.82rem;
  font-weight: 700;
  padding: 4px 12px;
  border-radius: 2px;
  letter-spacing: 0.5px;
}

.hero-title {
  font-size: 3.2rem;
  font-weight: 800;
  text-transform: UPPERCASE;
  line-height: 1.25;
  letter-spacing: 0;
  margin-bottom: 8px;
}

.hero-subtitle {
  font-size: 1.15rem;
  font-weight: 600;
  text-transform: UPPERCASE;
  color: var(--text-muted);
  letter-spacing: 0.5px;
  line-height: 1.4;
  margin-bottom: 24px;
  border-bottom: 2px solid var(--border-strong);
  padding-bottom: 10px;
}

.hero-footer-note {
  margin-top: 24px;
  padding-top: 12px;
  border-top: 1px solid var(--border);
  font-size: 0.88rem;
  color: var(--text-muted);
}

/* 18. MỤC LỤC GRID (TOC) */
.toc-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 10px;
}

.toc-item {
  border: 2px solid var(--border);
  border-left: 6px solid var(--primary);
  padding: 12px 16px;
  border-radius: 5px;
  display: flex;
  gap: 14px;
  align-items: center;
  background: var(--bg);
  cursor: pointer;
  transition: transform 0.2s ease, background 0.15s ease;
}

.toc-item:hover {
  transform: translateX(5px);
  background: var(--primary-light);
  border-color: var(--primary);
}

.toc-idx {
  font-size: 1.6rem;
  font-weight: 900;
  font-family: monospace;
  min-width: 38px;
  text-align: center;
  color: var(--secondary);
  border-right: 2px solid var(--secondary);
  padding-right: 10px;
}

.toc-desc h4 {
  font-size: 0.92rem;
  margin-bottom: 2px;
}

.toc-desc p {
  font-size: 0.8rem;
  color: var(--text-muted);
}

/* 19. KHUNG CÂU HỎI (SLIDE 12-17) */
.question-card,
.question-box,
.essay-card,
.quiz-slide {
  background: var(--bg);
  border: 2px solid var(--border-strong);
  padding: 24px;
  border-radius: 12px;
  box-shadow: 3px 3px 0 rgba(8, 145, 178, 0.15);
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.question-text,
.question-stem,
.quiz-question {
  font-size: 1.15rem;
  font-weight: 700;
  line-height: 1.55;
  color: var(--text);
}

.options,
.option-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.option,
.option-item {
  border: 2px solid var(--border);
  padding: 14px 16px;
  border-radius: 10px;
  font-size: 0.96rem;
  font-weight: 600;
  background: #ffffff;
  display: flex;
  align-items: center;
  gap: 12px;
  transition: all 0.2s ease;
  cursor: pointer;
  text-align: left;
  width: 100%;
}

.option:hover,
.option-item:hover {
  border-color: var(--primary);
  background: var(--primary-light);
  transform: translateX(4px);
}

.option.correct {
  border-color: var(--success);
  border-width: 4px;
  background: var(--success-light);
}

.option.wrong {
  border-color: var(--error);
  border-width: 4px;
  background: var(--error-light);
}

.option.locked {
  pointer-events: none;
  opacity: 0.5;
}

.option.correct.locked,
.option.wrong.locked {
  opacity: 1;
}

.opt-label,
.option-label {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 34px;
  height: 34px;
  border-radius: 50%;
  background: var(--primary);
  color: #fff;
  font-weight: 700;
  flex-shrink: 0;
}

.option.correct .option-label,
.option.correct .opt-label {
  background: var(--success);
}

.option.wrong .option-label,
.option.wrong .opt-label {
  background: var(--error);
}

.opt-label::after,
.option-label::after {
  content: "";
}

.option.correct .option-label::after,
.option.correct .opt-label::after {
  content: " ✓";
}

.option.wrong .option-label::after,
.option.wrong .opt-label::after {
  content: " ✗";
}

.quiz-actions,
.essay-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
}

.btn,
.reveal-btn,
.action-btn {
  border: 2px solid transparent;
  padding: 9px 18px;
  border-radius: 8px;
  font-size: 0.88rem;
  font-weight: 800;
  cursor: pointer;
  transition: all 0.15s ease;
}

.btn-reset,
.btn-hint,
.btn-answer {
  color: #fff;
}

.btn-hint {
  color: #ffffff;
  background: var(--accent);
}

.btn-answer {
  background: var(--primary);
}

.btn-reset {
  color: #ffffff;
  background: #6b7280;
}

.btn-reveal {
  color: #ffffff;
  background: var(--accent);
}

.btn:hover,
.reveal-btn:hover,
.action-btn:hover {
  filter: brightness(0.92);
}

.answer-box,
.hint-box,
.hint-card {
  margin-top: 8px;
  border-left: 6px solid var(--primary);
  padding: 14px 18px;
  border-radius: 8px;
  font-size: 0.95rem;
  line-height: 1.6;
}

.answer-box {
  background: var(--primary-light);
  border-left-color: var(--primary);
}

.hint-box {
  background: var(--accent-light);
  border-left-color: var(--accent);
}

.explanation-box {
  margin-top: 8px;
  padding: 14px 18px;
  border-left: 6px solid var(--accent);
  border-radius: 8px;
  background: var(--accent-light);
  color: var(--text);
  font-size: 0.95rem;
  line-height: 1.6;
}

.quiz-feedback {
  font-size: 1.06rem;
  font-weight: 700;
  padding: 12px 16px;
  border-radius: 8px;
  display: none;
}

.quiz-feedback.show {
  display: block;
}

.quiz-feedback.success {
  background: var(--success-light);
  color: var(--success);
}

.quiz-feedback.error {
  background: var(--error-light);
  color: var(--error);
}

.quiz-slide {
  position: relative;
}

.quiz-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
}

.quiz-score {
  font-size: 0.9rem;
  font-weight: 800;
  color: var(--primary);
  background: var(--primary-light);
  border: 1px solid var(--primary);
  border-radius: 999px;
  padding: 6px 12px;
}

.btn[disabled] {
  opacity: 0.65;
  cursor: default;
}

/* 20. TRANG KẾT THÚC (SLIDE 18) */
.end-inner {
  justify-content: center;
  text-align: center;
}

.end-title {
  font-size: 2.8rem;
}

.end-summary-box {
  text-align: left;
}

.end-button-group {
  display: flex;
  justify-content: center;
  gap: 14px;
  margin: 18px 0 20px 0;
}

.action-btn {
  background: var(--bg);
  color: var(--text);
  border: 2px solid var(--border-strong);
  padding: 8px 18px;
  border-radius: 4px;
  font-size: 0.88rem;
  font-weight: 800;
  cursor: pointer;
  transition: all 0.15s ease;
}

.action-btn:hover {
  background: var(--border-strong);
  color: var(--bg);
}

.primary-btn {
  background: var(--primary);
  color: #ffffff;
  border-color: var(--primary);
}

.primary-btn:hover {
  background: var(--primary-dark);
  border-color: var(--primary-dark);
}

.end-credit-line {
  font-size: 0.85rem;
  color: var(--text-muted);
}

/* 21. PRESENT MODE (CHẾ ĐỘ THUYẾT TRÌNH) */
body.present-mode .top-bar,
body.present-mode .footer-bar,
body.present-mode .progress-bar-container {
  display: none !important;
}

body.present-mode .exit-present-btn {
  display: block !important;
}

body.present-mode .slide {
  padding: 35px 50px;
}

body.present-mode .slide-inner {
  min-height: calc(100vh - 70px);
  border-width: 3px;
}

.exit-present-btn {
  display: none;
  position: fixed;
  top: 16px;
  right: 20px;
  z-index: 2000;
  background: var(--primary);
  color: var(--bg);
  border: 2px solid var(--primary);
  padding: 8px 18px;
  font-weight: 800;
  font-size: 0.88rem;
  cursor: pointer;
  border-radius: 4px;
  box-shadow: 0 4px 12px rgba(0,0,0,0.2);
}

.exit-present-btn:hover {
  background: var(--primary-dark);
}

/* 22. IN ẤN / XUẤT PDF (@media print) */
@media print {
  @page {
    size: A4 landscape;
    margin: 1cm;
  }

  html, body {
    width: 100% !important;
    height: auto !important;
    overflow: visible !important;
    background: #ffffff !important;
    color: #000000 !important;
  }

  .top-bar,
  .footer-bar,
  .progress-bar-container,
  .exit-present-btn,
  .end-button-group {
    display: none !important;
  }

  .presentation-stage {
    display: block !important;
    width: 100% !important;
    height: auto !important;
    overflow: visible !important;
  }

  .slide {
    position: relative !important;
    display: block !important;
    opacity: 1 !important;
    visibility: visible !important;
    width: 100% !important;
    height: auto !important;
    min-height: 95vh !important;
    padding: 0 !important;
    margin-bottom: 25px !important;
    page-break-after: always !important;
    break-after: page !important;
    transform: none !important;
  }

  .slide-inner {
    min-height: 95vh !important;
    border: 2px solid #000000 !important;
    page-break-inside: avoid;
  }
}

/* 23. RESPONSIVE */
@media (max-width: 1024px) {
  .slide {
    padding: 60px 24px 55px 24px;
  }

  .slide-inner {
    padding: 24px 18px;
  }

  .hero-title {
    font-size: 2.3rem;
  }

  .slide-title {
    font-size: 1.8rem;
  }

  .slide-split, .two-columns-simple {
    grid-template-columns: 1fr;
  }

  .mini-game-grid {
    grid-template-columns: 1fr;
  }

  .image-placeholder {
    min-height: 220px;
  }

  .stat-value {
    font-size: 2.3rem;
  }

  .chapter-badge {
    font-size: 6rem;
    top: 20px;
    right: 20px;
  }
}

@media (max-width: 600px) {
  .slide {
    padding: 55px 12px 50px 12px;
  }

  .slide-inner {
    padding: 16px 12px;
    border-width: 1.5px;
  }

  .top-bar-center, .lesson-tag {
    display: none;
  }

  .hero-title {
    font-size: 1.6rem;
  }

  .slide-title {
    font-size: 1.3rem;
  }
}

/* === EFFECT CHUYỂN ĐỘNG TỪNG BỘ PHẬN === */
.slide .animate-item {
  opacity: 0;
  transition: opacity 0.5s ease, transform 0.5s ease;
  transition-delay: var(--stagger-delay, 0s);
}

.slide.active .animate-item {
  opacity: 1;
  transform: translateY(0);
}

.slide .slide-title,
.slide .hero-title {
  opacity: 0;
  transform: translateY(-30px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.slide.active .slide-title,
.slide.active .hero-title {
  opacity: 1;
  transform: translateY(0);
}

.slide .chapter-badge {
  opacity: 0;
  transform: scale(0.5) rotate(-10deg);
  transition: opacity 0.8s ease, transform 0.8s cubic-bezier(0.34, 1.56, 0.64, 1);
}

.slide.active .chapter-badge {
  opacity: 0.12;
  transform: scale(1) rotate(0deg);
}

.slide .stat {
  opacity: 0;
  transform: translateY(30px) scale(0.9);
  transition: opacity 0.5s ease, transform 0.5s ease;
}

.slide.active .stat {
  opacity: 1;
  transform: translateY(0) scale(1);
}

.slide.active .stat.animate-item:hover {
  transform: translateY(-2px) scale(1);
}

.slide .content-card,
.slide .toc-item {
  opacity: 0;
  transform: translateX(-24px) scale(0.98);
  transition: opacity 0.5s ease, transform 0.5s ease, border-color 0.2s ease, box-shadow 0.2s ease;
}

.slide.active .content-card,
.slide.active .toc-item {
  opacity: 1;
  transform: translateX(0) scale(1);
}

.slide.active .content-card.animate-item:hover,
.slide.active .toc-item.animate-item:hover {
  transform: translateX(4px) scale(1);
}

.slide .academic-table {
  opacity: 0;
  transform: translateY(30px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.slide.active .academic-table {
  opacity: 1;
  transform: translateY(0);
}

.slide .academic-table tr {
  opacity: 0;
  transform: translateX(-20px);
  transition: opacity 0.4s ease, transform 0.4s ease;
}

.slide.active .academic-table tr {
  opacity: 1;
  transform: translateX(0);
}

.slide .note-box,
.slide .highlight-box {
  opacity: 0;
  transform: translateX(-30px);
  transition: opacity 0.5s ease, transform 0.5s ease;
}

.slide.active .note-box,
.slide.active .highlight-box {
  opacity: 1;
  transform: translateX(0);
}

.slide ul.bullet-list li,
.slide ul.clean-list li {
  opacity: 0;
  transform: translateX(-16px);
  transition: opacity 0.4s ease, transform 0.4s ease;
}

.slide.active ul.bullet-list li,
.slide.active ul.clean-list li {
  opacity: 1;
  transform: translateX(0);
}

.slide .image-placeholder {
  opacity: 0;
  transform: scale(0.95);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.slide.active .image-placeholder {
  opacity: 1;
  transform: scale(1);
}

.slide .option {
  opacity: 0;
  transform: translateX(-24px);
  transition: opacity 0.4s ease, transform 0.4s ease, border-color 0.2s ease, background-color 0.2s ease;
}

.slide.active .option {
  opacity: 1;
  transform: translateX(0);
}

.slide.active .option:hover:not(.locked) {
  transform: translateX(4px);
}

.slide.active .option.locked {
  opacity: 0.4;
}

.slide.active .option.correct.locked,
.slide.active .option.wrong.locked {
  opacity: 1;
}

.slide .btn,
.slide button {
  opacity: 0;
  transform: scale(0.9);
  transition: opacity 0.4s ease, transform 0.4s ease;
}

.slide.active .btn,
.slide.active button {
  opacity: 1;
  transform: scale(1);
}

.slide .hero-badge,
.slide .hero-subtitle,
.slide .question-text,
.slide .quiz-score,
.slide .quiz-feedback,
.slide .explanation-box,
.slide .hint-box,
.slide .answer-box,
.slide .essay-actions {
  opacity: 0;
  transform: translateY(18px);
  transition: opacity 0.5s ease, transform 0.5s ease;
}

.slide.active .hero-badge,
.slide.active .hero-subtitle,
.slide.active .question-text,
.slide.active .quiz-score,
.slide.active .quiz-feedback.show,
.slide.active .explanation-box,
.slide.active .hint-box,
.slide.active .answer-box,
.slide.active .essay-actions {
  opacity: 1;
  transform: translateY(0);
}

.slide .animate-item {
  transition-delay: var(--stagger-delay, 0s);
}

@media (max-width: 600px) {
  :root {
    --stagger-delay-0: 0.03s;
    --stagger-delay-1: 0.11s;
    --stagger-delay-2: 0.19s;
    --stagger-delay-3: 0.27s;
    --stagger-delay-4: 0.35s;
    --stagger-delay-5: 0.43s;
    --stagger-delay-6: 0.51s;
    --stagger-delay-7: 0.59s;
  }
}

@media (prefers-reduced-motion: reduce) {
  :root {
    --stagger-delay-0: 0s;
    --stagger-delay-1: 0s;
    --stagger-delay-2: 0s;
    --stagger-delay-3: 0s;
    --stagger-delay-4: 0s;
    --stagger-delay-5: 0s;
    --stagger-delay-6: 0s;
    --stagger-delay-7: 0s;
  }

  .slide .animate-item,
  .slide .slide-title,
  .slide .hero-title,
  .slide .chapter-badge,
  .slide .stat,
  .slide .content-card,
  .slide .toc-item,
  .slide .academic-table,
  .slide .academic-table tr,
  .slide .note-box,
  .slide .highlight-box,
  .slide ul.bullet-list li,
  .slide ul.clean-list li,
  .slide .image-placeholder,
  .slide .option,
  .slide .btn,
  .slide button,
  .slide .hero-badge,
  .slide .hero-subtitle,
  .slide .question-text,
  .slide .quiz-score,
  .slide .quiz-feedback,
  .slide .explanation-box,
  .slide .hint-box,
  .slide .answer-box,
  .slide .essay-actions {
    transition-duration: 0.01ms !important;
    transition-delay: 0ms !important;
  }
}

@media print {
  .slide .animate-item,
  .slide .slide-title,
  .slide .hero-title,
  .slide .chapter-badge,
  .slide .stat,
  .slide .content-card,
  .slide .toc-item,
  .slide .academic-table,
  .slide .academic-table tr,
  .slide .note-box,
  .slide .highlight-box,
  .slide ul.bullet-list li,
  .slide ul.clean-list li,
  .slide .image-placeholder,
  .slide .option,
  .slide .btn,
  .slide button,
  .slide .hero-badge,
  .slide .hero-subtitle,
  .slide .question-text,
  .slide .quiz-score {
    opacity: 1 !important;
    transform: none !important;
    transition: none !important;
  }
}

@media print {
  .slide .chapter-badge {
    opacity: 0.12 !important;
    transform: none !important;
    transition: none !important;
  }
}

/* Vietnamese-friendly typography */
h1,
h2,
h3,
.slide-title,
.slide .hero-title {
  font-family: 'Be Vietnam Pro', 'Segoe UI', sans-serif;
  font-weight: 800;
  letter-spacing: 0;
  line-height: 1.25;
  word-spacing: 0.05em;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
}

.chapter-badge,
.stat-value,
.stat-label,
.content-card h3,
.option-text,
.question-text,
.btn,
.reveal-btn,
.action-btn,
button {
  font-family: 'Be Vietnam Pro', 'Segoe UI', sans-serif;
}

.chapter-badge {
  font-weight: 800;
}

.stat-value {
  font-weight: 800;
}

.stat-label {
  font-weight: 700;
}

.option-text {
  font-weight: 600;
}

.btn,
.reveal-btn,
.action-btn,
button {
  font-feature-settings: "kern" 1, "liga" 1, "calt" 1;
  font-variant-ligatures: common-ligatures;
}