/* ==========================================================================
   Rajasthan Art & Culture (राजस्थान कला एवं संस्कृति) - Design System & CSS
   ========================================================================== */

@import url('https://fonts.googleapis.com/css2?family=Mukta:wght@300;400;500;600;700;800&family=Outfit:wght@300;400;500;600;700;800&family=Fira+Code:wght@400;500&display=swap');

:root {
  /* Color Palette */
  --bg-dark: #090d16;
  --bg-card: rgba(15, 23, 42, 0.75);
  --bg-card-hover: rgba(30, 41, 59, 0.85);
  --bg-header: rgba(15, 23, 42, 0.9);
  --bg-sidebar: rgba(11, 17, 32, 0.95);
  
  --border-color: rgba(255, 255, 255, 0.08);
  --border-glow: rgba(245, 158, 11, 0.3);
  
  --primary: #f59e0b;        /* Amber Gold */
  --primary-light: #fbbf24;
  --primary-dark: #d97706;
  --primary-glow: rgba(245, 158, 11, 0.25);

  --secondary: #06b6d4;      /* Cyan Accent */
  --accent-rose: #f43f5e;     /* Crimson/Rose */
  --accent-emerald: #10b981;  /* Emerald Green */
  --accent-purple: #a855f7;   /* Purple */
  
  --text-main: #f8fafc;
  --text-muted: #94a3b8;
  --text-dim: #64748b;
  
  --font-main: 'Mukta', 'Noto Sans Devanagari', -apple-system, sans-serif;
  --font-heading: 'Outfit', 'Mukta', sans-serif;
  --font-mono: 'Fira Code', monospace;
  
  --sidebar-width: 320px;
  --header-height: 70px;
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 18px;
  --radius-full: 9999px;
  
  --transition-fast: 0.2s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-normal: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  
  --glass-shadow: 0 8px 32px 0 rgba(0, 0, 0, 0.37);
  --glow-shadow: 0 0 20px rgba(245, 158, 11, 0.15);
}

/* Reset & Base */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
  font-size: 16px;
}

body {
  font-family: var(--font-main);
  background-color: var(--bg-dark);
  background-image: 
    radial-gradient(at 10% 10%, rgba(245, 158, 11, 0.05) 0px, transparent 50%),
    radial-gradient(at 90% 90%, rgba(6, 182, 212, 0.05) 0px, transparent 50%),
    radial-gradient(at 50% 50%, rgba(168, 85, 247, 0.03) 0px, transparent 50%);
  background-attachment: fixed;
  color: var(--text-main);
  line-height: 1.7;
  min-height: 100vh;
  overflow-x: hidden;
}

/* Custom Scrollbar */
::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}
::-webkit-scrollbar-track {
  background: rgba(15, 23, 42, 0.6);
}
::-webkit-scrollbar-thumb {
  background: rgba(245, 158, 11, 0.3);
  border-radius: 4px;
}
::-webkit-scrollbar-thumb:hover {
  background: var(--primary);
}

/* ==========================================================================
   Header & Navbar
   ========================================================================== */
.app-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--header-height);
  background: var(--bg-header);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border-color);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 1.5rem;
  z-index: 1000;
  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.2);
}

.header-left {
  display: flex;
  align-items: center;
  gap: 1rem;
}

.mobile-toggle-btn {
  display: none;
  background: transparent;
  border: 1px solid var(--border-color);
  color: var(--text-main);
  font-size: 1.25rem;
  width: 42px;
  height: 42px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  align-items: center;
  justify-content: center;
  transition: var(--transition-fast);
}
.mobile-toggle-btn:hover {
  border-color: var(--primary);
  color: var(--primary);
}

.brand-logo {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  text-decoration: none;
}
.logo-icon {
  width: 42px;
  height: 42px;
  background: linear-gradient(135deg, var(--primary), var(--primary-dark));
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.5rem;
  box-shadow: var(--glow-shadow);
}
.logo-text {
  display: flex;
  flex-direction: column;
}
.logo-title {
  font-family: var(--font-heading);
  font-weight: 700;
  font-size: 1.2rem;
  color: #fff;
  letter-spacing: -0.02em;
  background: linear-gradient(135deg, #ffffff 0%, var(--primary-light) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}
.logo-subtitle {
  font-size: 0.75rem;
  color: var(--secondary);
  font-weight: 500;
}

/* Global Search */
.header-search {
  position: relative;
  width: 320px;
}
.search-input {
  width: 100%;
  padding: 0.55rem 1rem 0.55rem 2.6rem;
  background: rgba(15, 23, 42, 0.6);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-full);
  color: var(--text-main);
  font-size: 0.9rem;
  outline: none;
  transition: var(--transition-fast);
}
.search-input:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 3px var(--primary-glow);
  background: rgba(15, 23, 42, 0.9);
}
.search-icon {
  position: absolute;
  left: 0.9rem;
  top: 50%;
  transform: translateY(-50%);
  color: var(--text-dim);
  pointer-events: none;
  font-size: 0.9rem;
}

/* Header Controls & Dual Switcher */
.header-actions {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.view-mode-toggle {
  display: flex;
  background: rgba(30, 41, 59, 0.7);
  padding: 4px;
  border-radius: var(--radius-full);
  border: 1px solid var(--border-color);
}
.view-btn {
  background: transparent;
  border: none;
  color: var(--text-muted);
  padding: 0.4rem 1rem;
  border-radius: var(--radius-full);
  font-size: 0.85rem;
  font-weight: 600;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 0.4rem;
  transition: var(--transition-fast);
  font-family: var(--font-main);
}
.view-btn.active {
  background: linear-gradient(135deg, var(--primary), var(--primary-dark));
  color: #000;
  box-shadow: var(--glow-shadow);
}

.icon-action-btn {
  background: rgba(30, 41, 59, 0.6);
  border: 1px solid var(--border-color);
  color: var(--text-main);
  padding: 0.5rem 0.85rem;
  border-radius: var(--radius-md);
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.85rem;
  font-weight: 600;
  transition: var(--transition-fast);
  font-family: var(--font-main);
  text-decoration: none;
}
.icon-action-btn:hover {
  border-color: var(--primary);
  color: var(--primary-light);
  transform: translateY(-1px);
}

/* Course Switcher Dropdown */
.course-switcher-dropdown {
  position: relative;
  display: inline-block;
}
.course-switcher-btn {
  background: linear-gradient(135deg, rgba(6, 182, 212, 0.2), rgba(15, 23, 42, 0.8));
  border: 1px solid var(--secondary);
  color: #67e8f9;
  padding: 0.45rem 0.95rem;
  border-radius: var(--radius-full);
  cursor: pointer;
  font-size: 0.85rem;
  font-weight: 700;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  transition: var(--transition-fast);
  font-family: var(--font-main);
}
.course-switcher-btn:hover {
  background: var(--secondary);
  color: #000;
  box-shadow: 0 0 15px rgba(6, 182, 212, 0.4);
}

.course-menu-content {
  display: none;
  position: absolute;
  top: 120%;
  right: 0;
  background: rgba(11, 17, 32, 0.95);
  backdrop-filter: blur(16px);
  min-width: 240px;
  border: 1px solid var(--border-glow);
  border-radius: var(--radius-md);
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.5);
  padding: 0.5rem;
  z-index: 1100;
}
.course-switcher-dropdown:hover .course-menu-content {
  display: block;
  animation: fadeIn 0.2s ease-out;
}

.course-menu-item {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.65rem 0.85rem;
  color: var(--text-main);
  text-decoration: none;
  font-size: 0.9rem;
  font-weight: 600;
  border-radius: var(--radius-sm);
  transition: var(--transition-fast);
}
.course-menu-item:hover {
  background: rgba(30, 41, 59, 0.8);
  color: var(--primary-light);
}
.course-menu-item.active {
  background: rgba(245, 158, 11, 0.15);
  color: var(--primary-light);
  border-left: 3px solid var(--primary);
}

/* Sidebar Subject Switcher Card */
.sidebar-subjects-card {
  padding: 1rem 1.25rem;
  border-bottom: 1px solid var(--border-color);
  background: rgba(15, 23, 42, 0.5);
}
.sidebar-subjects-title {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--secondary);
  font-weight: 700;
  margin-bottom: 0.6rem;
}
.sidebar-subject-links {
  display: flex;
  flex-direction: column;
  gap: 6px;
}
.sidebar-subject-btn {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  padding: 0.5rem 0.75rem;
  border-radius: var(--radius-sm);
  background: rgba(30, 41, 59, 0.5);
  border: 1px solid var(--border-color);
  color: var(--text-main);
  text-decoration: none;
  font-size: 0.85rem;
  font-weight: 600;
  transition: var(--transition-fast);
}
.sidebar-subject-btn:hover {
  border-color: var(--primary);
  color: var(--primary-light);
  transform: translateX(3px);
}
.sidebar-subject-btn.active {
  border-color: var(--primary);
  background: rgba(245, 158, 11, 0.15);
  color: var(--primary-light);
}

/* ==========================================================================
   App Layout
   ========================================================================== */
.app-container {
  display: flex;
  margin-top: var(--header-height);
  min-height: calc(100vh - var(--header-height));
}

/* Sidebar */
.app-sidebar {
  width: var(--sidebar-width);
  background: var(--bg-sidebar);
  border-right: 1px solid var(--border-color);
  position: fixed;
  top: var(--header-height);
  bottom: 0;
  left: 0;
  overflow-y: auto;
  z-index: 900;
  transition: transform var(--transition-normal);
  display: flex;
  flex-direction: column;
}

.sidebar-header {
  padding: 1.25rem 1.25rem 0.75rem 1.25rem;
  border-bottom: 1px solid var(--border-color);
}
.sidebar-title {
  font-size: 0.85rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--primary-light);
  font-weight: 700;
  margin-bottom: 0.75rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.sidebar-search-box {
  position: relative;
}
.sidebar-search-input {
  width: 100%;
  padding: 0.5rem 0.8rem 0.5rem 2.2rem;
  background: rgba(15, 23, 42, 0.8);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  color: var(--text-main);
  font-size: 0.85rem;
  outline: none;
}
.sidebar-search-input:focus {
  border-color: var(--primary);
}

.chapter-nav {
  padding: 0.75rem;
  flex: 1;
}
.chapter-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 4px;
}
.chapter-item-link {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.75rem 1rem;
  border-radius: var(--radius-md);
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.95rem;
  font-weight: 500;
  transition: var(--transition-fast);
  border: 1px solid transparent;
}
.chapter-item-link:hover {
  background: rgba(30, 41, 59, 0.6);
  color: var(--text-main);
  border-color: var(--border-color);
}
.chapter-item-link.active {
  background: linear-gradient(90deg, rgba(245, 158, 11, 0.15), transparent);
  border-left: 4px solid var(--primary);
  color: #fff;
  font-weight: 600;
}
.chapter-num-badge {
  background: rgba(255, 255, 255, 0.08);
  color: var(--primary-light);
  font-size: 0.75rem;
  font-weight: 700;
  padding: 2px 8px;
  border-radius: var(--radius-full);
  min-width: 28px;
  text-align: center;
}
.chapter-item-link.active .chapter-num-badge {
  background: var(--primary);
  color: #000;
}

/* Sidebar Footer / Stats */
.sidebar-footer {
  padding: 1rem 1.25rem;
  border-top: 1px solid var(--border-color);
  background: rgba(9, 13, 22, 0.8);
  font-size: 0.8rem;
  color: var(--text-dim);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

/* Main Content Area */
.app-main {
  margin-left: var(--sidebar-width);
  flex: 1;
  padding: 2rem 2.5rem 6rem 2.5rem;
  max-width: 1200px;
  width: 100%;
  transition: var(--transition-normal);
}

/* Focus Mode State */
body.focus-mode .app-sidebar {
  transform: translateX(-100%);
}
body.focus-mode .app-main {
  margin-left: 0;
  max-width: 1000px;
  margin-x: auto;
}
body.focus-mode .app-header {
  opacity: 0.3;
  transition: opacity 0.2s;
}
body.focus-mode .app-header:hover {
  opacity: 1;
}

/* ==========================================================================
   Chapter Page Styling & Typography
   ========================================================================== */
.chapter-container {
  animation: fadeIn 0.3s ease-out;
}
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

.chapter-header-card {
  background: linear-gradient(135deg, rgba(30, 41, 59, 0.8), rgba(15, 23, 42, 0.9));
  border: 1px solid var(--border-glow);
  border-radius: var(--radius-lg);
  padding: 2rem;
  margin-bottom: 2rem;
  position: relative;
  overflow: hidden;
  box-shadow: var(--glass-shadow);
}
.chapter-header-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 6px;
  height: 100%;
  background: linear-gradient(to bottom, var(--primary), var(--secondary));
}

.chapter-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  background: rgba(245, 158, 11, 0.15);
  border: 1px solid rgba(245, 158, 11, 0.3);
  color: var(--primary-light);
  padding: 0.25rem 0.85rem;
  border-radius: var(--radius-full);
  font-size: 0.85rem;
  font-weight: 700;
  margin-bottom: 0.75rem;
}

.chapter-title-main {
  font-family: var(--font-heading);
  font-size: 2.2rem;
  font-weight: 800;
  color: #ffffff;
  line-height: 1.3;
  margin-bottom: 0.5rem;
}
.chapter-subtitle-meta {
  color: var(--text-muted);
  font-size: 0.95rem;
  display: flex;
  gap: 1.5rem;
  flex-wrap: wrap;
}

/* View Mode Sections Control */
.view-mode-section {
  display: none;
}
body.mode-detailed .view-mode-detailed {
  display: block;
}
body.mode-notes .view-mode-notes {
  display: block;
}

/* Topic Card Container */
.topic-card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.75rem;
  margin-bottom: 1.75rem;
  backdrop-filter: blur(10px);
  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.2);
  transition: var(--transition-fast);
}
.topic-card:hover {
  border-color: rgba(245, 158, 11, 0.25);
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.3);
}

.topic-title {
  font-size: 1.4rem;
  font-weight: 700;
  color: var(--primary-light);
  margin-bottom: 1rem;
  padding-bottom: 0.5rem;
  border-bottom: 1px solid rgba(255, 255, 255, 0.08);
  display: flex;
  align-items: center;
  gap: 0.6rem;
}
.topic-subtitle {
  font-size: 1.15rem;
  font-weight: 600;
  color: var(--secondary);
  margin: 1.2rem 0 0.6rem 0;
}

/* Content Elements */
p {
  margin-bottom: 1rem;
  color: #e2e8f0;
  font-size: 1.05rem;
  line-height: 1.8;
}

/* Fact Badges & Highlights */
.fact-badge {
  display: inline-block;
  background: rgba(6, 182, 212, 0.15);
  border: 1px solid rgba(6, 182, 212, 0.3);
  color: #67e8f9;
  font-size: 0.8rem;
  font-weight: 700;
  padding: 2px 8px;
  border-radius: var(--radius-sm);
  margin-right: 6px;
}
.trick-box {
  background: linear-gradient(135deg, rgba(168, 85, 247, 0.12), rgba(244, 63, 94, 0.08));
  border-left: 4px solid var(--accent-purple);
  padding: 1rem 1.25rem;
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  margin: 1.25rem 0;
  color: #f3e8ff;
}
.trick-title {
  font-weight: 700;
  color: var(--accent-purple);
  font-size: 0.95rem;
  margin-bottom: 0.3rem;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.alert-info {
  background: rgba(245, 158, 11, 0.08);
  border-left: 4px solid var(--primary);
  padding: 1rem 1.25rem;
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  margin: 1.25rem 0;
}

/* Data Tables */
.table-responsive {
  width: 100%;
  overflow-x: auto;
  margin: 1.25rem 0;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
}
.data-table {
  width: 100%;
  border-collapse: collapse;
  text-align: left;
  font-size: 0.98rem;
}
.data-table th {
  background: rgba(30, 41, 59, 0.9);
  color: var(--primary-light);
  padding: 0.85rem 1rem;
  font-weight: 700;
  border-bottom: 2px solid var(--border-color);
  white-space: nowrap;
}
.data-table td {
  padding: 0.8rem 1rem;
  border-bottom: 1px solid rgba(255, 255, 255, 0.05);
  color: #cbd5e1;
}
.data-table tr:hover td {
  background: rgba(255, 255, 255, 0.03);
}

/* Bullet Lists (Quick Notes Mode) */
.bullet-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  margin-top: 0.75rem;
}
.bullet-item {
  position: relative;
  padding-left: 1.75rem;
  color: #e2e8f0;
  font-size: 1.05rem;
  line-height: 1.7;
}
.bullet-item::before {
  content: '⚡';
  position: absolute;
  left: 0;
  top: 2px;
  font-size: 0.9rem;
}

/* SVG Diagrams Container */
.svg-diagram-wrapper {
  background: rgba(9, 13, 22, 0.9);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  margin: 1.5rem 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
}
.svg-diagram-title {
  font-size: 0.9rem;
  color: var(--secondary);
  font-weight: 600;
  margin-bottom: 1rem;
  text-align: center;
}

/* ==========================================================================
   MCQ Quiz Section Styling
   ========================================================================== */
.quiz-wrapper {
  background: linear-gradient(135deg, rgba(15, 23, 42, 0.95), rgba(9, 13, 22, 0.98));
  border: 2px solid var(--primary-glow);
  border-radius: var(--radius-lg);
  padding: 2rem;
  margin-top: 3rem;
  box-shadow: 0 10px 40px rgba(0, 0, 0, 0.4);
}

.quiz-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-bottom: 1rem;
  border-bottom: 1px solid var(--border-color);
  margin-bottom: 1.5rem;
  flex-wrap: wrap;
  gap: 1rem;
}
.quiz-title {
  font-size: 1.5rem;
  font-weight: 800;
  color: #fff;
  display: flex;
  align-items: center;
  gap: 0.6rem;
}
.quiz-score-badge {
  background: rgba(16, 185, 129, 0.15);
  border: 1px solid var(--accent-emerald);
  color: var(--accent-emerald);
  padding: 0.4rem 1rem;
  border-radius: var(--radius-full);
  font-weight: 700;
  font-size: 0.9rem;
}

.quiz-card {
  background: rgba(30, 41, 59, 0.5);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  margin-bottom: 1.25rem;
  transition: var(--transition-fast);
}

.quiz-question {
  font-size: 1.1rem;
  font-weight: 700;
  color: #fff;
  margin-bottom: 1rem;
  line-height: 1.6;
}

.quiz-options {
  display: grid;
  grid-template-columns: 1fr;
  gap: 0.6rem;
}

.option-btn {
  background: rgba(15, 23, 42, 0.8);
  border: 1px solid var(--border-color);
  color: #cbd5e1;
  padding: 0.8rem 1.2rem;
  border-radius: var(--radius-sm);
  text-align: left;
  font-size: 0.98rem;
  font-family: var(--font-main);
  cursor: pointer;
  transition: var(--transition-fast);
  display: flex;
  align-items: center;
  gap: 0.75rem;
}
.option-btn:hover:not(:disabled) {
  background: rgba(30, 41, 59, 0.9);
  border-color: var(--primary);
  color: #fff;
}
.option-btn:disabled {
  cursor: default;
}

/* Answer Feedback States */
.option-btn.correct {
  background: rgba(16, 185, 129, 0.25) !important;
  border-color: var(--accent-emerald) !important;
  color: #a7f3d0 !important;
  font-weight: 700;
}
.option-btn.wrong {
  background: rgba(244, 63, 94, 0.25) !important;
  border-color: var(--accent-rose) !important;
  color: #fecdd3 !important;
}

.quiz-explanation {
  display: none;
  background: rgba(16, 185, 129, 0.1);
  border-left: 4px solid var(--accent-emerald);
  padding: 0.85rem 1rem;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  margin-top: 0.85rem;
  font-size: 0.92rem;
  color: #d1fae5;
}

.quiz-actions {
  display: flex;
  justify-content: flex-end;
  margin-top: 1.5rem;
}
.retry-quiz-btn {
  background: linear-gradient(135deg, var(--primary), var(--primary-dark));
  border: none;
  color: #000;
  padding: 0.6rem 1.5rem;
  border-radius: var(--radius-full);
  font-weight: 700;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  transition: var(--transition-fast);
}
.retry-quiz-btn:hover {
  transform: scale(1.03);
  box-shadow: var(--glow-shadow);
}

/* ==========================================================================
   Sticky Bottom Navigation Bar
   ========================================================================== */
.bottom-nav {
  position: fixed;
  bottom: 0;
  left: var(--sidebar-width);
  right: 0;
  height: 60px;
  background: rgba(9, 13, 22, 0.95);
  backdrop-filter: blur(12px);
  border-top: 1px solid var(--border-color);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 2rem;
  z-index: 800;
  transition: var(--transition-normal);
}
body.focus-mode .bottom-nav {
  left: 0;
}

.nav-ch-btn {
  background: rgba(30, 41, 59, 0.7);
  border: 1px solid var(--border-color);
  color: var(--text-main);
  padding: 0.45rem 1.2rem;
  border-radius: var(--radius-full);
  text-decoration: none;
  font-size: 0.9rem;
  font-weight: 600;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  transition: var(--transition-fast);
}
.nav-ch-btn:hover:not(.disabled) {
  border-color: var(--primary);
  color: var(--primary-light);
  transform: translateY(-2px);
}
.nav-ch-btn.disabled {
  opacity: 0.4;
  pointer-events: none;
}

/* ==========================================================================
   Responsive Rules
   ========================================================================== */
@media (max-width: 1024px) {
  :root {
    --sidebar-width: 280px;
  }
  .app-main {
    padding: 1.5rem 1.5rem 5rem 1.5rem;
  }
}

@media (max-width: 768px) {
  .mobile-toggle-btn {
    display: flex;
  }
  .app-sidebar {
    transform: translateX(-100%);
    width: 300px;
    box-shadow: 10px 0 30px rgba(0,0,0,0.5);
  }
  body.sidebar-open .app-sidebar {
    transform: translateX(0);
  }
  .app-main {
    margin-left: 0;
    padding: 1.25rem 1rem 5rem 1rem;
  }
  .bottom-nav {
    left: 0;
    padding: 0 1rem;
  }
  .header-search {
    display: none;
  }
  .logo-subtitle {
    display: none;
  }
  .chapter-title-main {
    font-size: 1.6rem;
  }
}

/* Print CSS Overrides */
@media print {
  .app-header, .app-sidebar, .bottom-nav, .view-mode-toggle, .quiz-wrapper, .retry-quiz-btn {
    display: none !important;
  }
  body {
    background: #fff !important;
    color: #000 !important;
  }
  .app-main {
    margin: 0 !important;
    padding: 0 !important;
    max-width: 100% !important;
  }
  .topic-card {
    border: 1px solid #ccc !important;
    background: #fff !important;
    color: #000 !important;
    break-inside: avoid;
  }
  .topic-title {
    color: #000 !important;
  }
}