@import url('https://fonts.googleapis.com/css2?family=JetBrains+Mono:wght@400;500;600;700&family=Outfit:wght@400;500;600;700;800;900&family=Plus+Jakarta+Sans:ital,wght@0,400;0,500;0,600;0,700;0,800;1,400;1,600&display=swap');

:root {
  --bg-primary: #f8fafc;
  --bg-secondary: #ffffff;
  --bg-card: #ffffff;
  --bg-subtle: #f1f5f9;
  --bg-step: #f8fafc;
  --bg-active-step: #eff6ff;

  --text-primary: #0f172a;
  --text-secondary: #334155;
  --text-muted: #64748b;

  --border-color: #e2e8f0;
  --border-subtle: #f1f5f9;
  --border-focus: #4f46e5;

  /* Grade Specific Palette */
  --grade-7mo: #0284c7;
  --grade-8vo: #059669;
  --grade-9no: #7c3aed;
  --grade-10mo: #d97706;
  --grade-11mo: #0891b2;
  --grade-12mo: #e11d48;

  --accent-current: #0284c7;
  --accent-current-light: rgba(2, 132, 199, 0.09);

  --radius-xs: 6px;
  --radius-sm: 10px;
  --radius-md: 14px;
  --radius-lg: 20px;

  --shadow-sm: 0 1px 3px rgba(15, 23, 42, 0.05);
  --shadow-card: 0 2px 8px rgba(15, 23, 42, 0.04), 0 0 0 1px var(--border-color);
  --shadow-hover: 0 8px 20px -3px rgba(15, 23, 42, 0.08), 0 0 0 1px var(--border-color);

  --font-display: 'Outfit', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-body: 'Plus Jakarta Sans', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'JetBrains Mono', monospace;

  --transition-fast: 0.15s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-smooth: 0.25s cubic-bezier(0.4, 0, 0.2, 1);
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  -webkit-tap-highlight-color: transparent;
}

html {
  scroll-behavior: smooth;
  text-size-adjust: 100%;
  -webkit-text-size-adjust: 100%;
  overflow-x: hidden;
}

body {
  font-family: var(--font-body);
  background-color: var(--bg-primary);
  background-image:
    radial-gradient(ellipse 60% 40% at 50% -10%, rgba(99, 102, 241, 0.04) 0%, transparent 60%),
    radial-gradient(ellipse 50% 30% at 85% 100%, rgba(2, 132, 199, 0.03) 0%, transparent 50%);
  color: var(--text-primary);
  line-height: 1.6;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
  padding-bottom: 74px; /* Space for mobile bottom bar */
}

@media (min-width: 769px) {
  body {
    padding-bottom: 0;
  }
}

/* Typography Base */
h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-display);
  font-weight: 700;
  color: var(--text-primary);
  letter-spacing: -0.02em;
}

/* Scrollbars */
::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: #cbd5e1; border-radius: 4px; }
::-webkit-scrollbar-thumb:hover { background: #94a3b8; }

/* Utilities */
.hidden { display: none !important; }

/* MathJax Responsive Container */
mjx-container {
  overflow-x: auto !important;
  overflow-y: hidden !important;
  max-width: 100% !important;
  padding: 4px 0 !important;
  vertical-align: middle !important;
  font-size: 105% !important;
  -webkit-overflow-scrolling: touch !important;
}

mjx-container[jax="CHTML"][display="true"] {
  margin: 0.6em 0 !important;
}

.math-scrollable {
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
  max-width: 100%;
  scrollbar-width: thin;
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  min-height: 42px;
  padding: 8px 16px;
  border-radius: var(--radius-sm);
  font-family: var(--font-body);
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  border: 1px solid transparent;
  transition: all var(--transition-fast);
  text-decoration: none;
  white-space: nowrap;
  user-select: none;
  touch-action: manipulation;
}

.btn-primary {
  background: var(--accent-current);
  color: #ffffff;
}
.btn-primary:hover {
  filter: brightness(1.08);
  transform: translateY(-1px);
}
.btn-primary:active {
  transform: translateY(0);
  filter: brightness(0.95);
}

.btn-secondary {
  background: #ffffff;
  color: var(--text-secondary);
  border: 1px solid var(--border-color);
}
.btn-secondary:hover {
  background: var(--bg-subtle);
  color: var(--text-primary);
  border-color: #cbd5e1;
}
.btn-secondary:active { background: #e2e8f0; }

.btn-ghost {
  background: transparent;
  color: var(--text-secondary);
}
.btn-ghost:hover {
  background: var(--bg-subtle);
  color: var(--text-primary);
}
.btn-ghost:active { background: #e2e8f0; }

.btn-sm { min-height: 36px; padding: 6px 12px; font-size: 0.84rem; }
.btn-xs { min-height: 32px; padding: 4px 10px; font-size: 0.78rem; }

/* =============================================================================
   HEADER & TOP BAR
   ============================================================================= */
.site-header {
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border-color);
  position: sticky;
  top: 0;
  z-index: 1000;
  box-shadow: 0 2px 8px rgba(15, 23, 42, 0.03);
}

.header-content {
  max-width: 1200px;
  margin: 0 auto;
  padding: 12px 16px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
}

.brand-row {
  display: flex;
  align-items: center;
  gap: 10px;
  min-width: 0;
}

.header-icon {
  font-size: 1.5rem;
  background: var(--bg-subtle);
  width: 38px;
  height: 38px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  flex-shrink: 0;
}

.brand-text {
  min-width: 0;
}

.site-header h1 {
  font-size: 1.15rem;
  font-weight: 800;
  letter-spacing: -0.02em;
  color: var(--text-primary);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  line-height: 1.25;
}

.site-header .subtitle {
  font-size: 0.75rem;
  color: var(--text-muted);
  font-weight: 500;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 10px;
}

/* Search Box */
.search-box {
  display: flex;
  align-items: center;
  background: var(--bg-subtle);
  border: 1px solid var(--border-color);
  border-radius: 100px;
  padding: 4px 12px;
  min-height: 38px;
  width: 240px;
  transition: all var(--transition-fast);
}

.search-box:focus-within {
  border-color: var(--accent-current);
  background: #ffffff;
  box-shadow: 0 0 0 3px var(--accent-current-light);
  width: 280px;
}

.search-icon {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-right: 6px;
  flex-shrink: 0;
}

.search-box input {
  border: none;
  background: transparent;
  width: 100%;
  font-family: var(--font-body);
  font-size: 0.84rem;
  color: var(--text-primary);
  outline: none;
}
.search-box input::placeholder { color: #94a3b8; }

.search-clear {
  border: none;
  background: none;
  color: var(--text-muted);
  cursor: pointer;
  padding: 4px 8px;
  font-size: 0.85rem;
}
.search-clear:hover { color: var(--text-primary); }

.stats-pills {
  display: flex;
  align-items: center;
  gap: 8px;
}

.stat-pill {
  display: flex;
  align-items: center;
  gap: 5px;
  background: var(--bg-subtle);
  border: 1px solid var(--border-color);
  padding: 4px 10px;
  min-height: 36px;
  border-radius: 100px;
  font-size: 0.8rem;
  color: var(--text-secondary);
  white-space: nowrap;
}
.stat-pill strong {
  color: var(--text-primary);
  font-weight: 700;
  font-family: var(--font-display);
}

.btn-print {
  background: #ffffff;
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
  min-height: 36px;
}
.btn-print:hover {
  background: var(--bg-subtle);
  color: var(--text-primary);
}

/* =============================================================================
   GRADE SELECTOR (Responsive Grid - NO Horizontal Scroll!)
   ============================================================================= */
.grade-nav {
  max-width: 1200px;
  margin: 0 auto;
  padding: 4px 16px 8px;
  display: grid;
  grid-template-columns: repeat(6, 1fr);
  gap: 8px;
  width: 100%;
}

.grade-btn {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 10px;
  min-height: 44px;
  border-radius: var(--radius-sm);
  background: var(--bg-subtle);
  border: 1.5px solid transparent;
  cursor: pointer;
  text-align: left;
  transition: all var(--transition-fast);
  touch-action: manipulation;
  user-select: none;
  width: 100%;
}

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

.grade-btn.active {
  background: #ffffff;
  border-color: var(--accent-current);
  box-shadow: 0 2px 8px rgba(15, 23, 42, 0.06);
}

.grade-badge {
  font-family: var(--font-display);
  font-size: 0.85rem;
  font-weight: 800;
  width: 30px;
  height: 30px;
  border-radius: 8px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--bg-subtle);
  color: var(--text-secondary);
  flex-shrink: 0;
  transition: all var(--transition-fast);
}

.grade-btn[data-grade="7mo"] .grade-badge { background: #e0f2fe; color: #0369a1; }
.grade-btn[data-grade="8vo"] .grade-badge { background: #d1fae5; color: #047857; }
.grade-btn[data-grade="9no"] .grade-badge { background: #ede9fe; color: #6d28d9; }
.grade-btn[data-grade="10mo"] .grade-badge { background: #fef3c7; color: #b45309; }
.grade-btn[data-grade="11mo"] .grade-badge { background: #cffafe; color: #0e7490; }
.grade-btn[data-grade="12mo"] .grade-badge { background: #ffe4e6; color: #be123c; }

.grade-btn.active .grade-badge {
  color: #ffffff;
}
.grade-btn.active[data-grade="7mo"] .grade-badge { background: var(--grade-7mo); }
.grade-btn.active[data-grade="8vo"] .grade-badge { background: var(--grade-8vo); }
.grade-btn.active[data-grade="9no"] .grade-badge { background: var(--grade-9no); }
.grade-btn.active[data-grade="10mo"] .grade-badge { background: var(--grade-10mo); }
.grade-btn.active[data-grade="11mo"] .grade-badge { background: var(--grade-11mo); }
.grade-btn.active[data-grade="12mo"] .grade-badge { background: var(--grade-12mo); }

.grade-btn-info {
  display: flex;
  flex-direction: column;
  min-width: 0;
}

.grade-name {
  font-family: var(--font-display);
  font-size: 0.82rem;
  font-weight: 700;
  color: var(--text-primary);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.grade-desc {
  font-size: 0.7rem;
  color: var(--text-muted);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

/* =============================================================================
   MAIN CONTAINER & HERO BANNER
   ============================================================================= */
.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 16px 16px 60px;
  width: 100%;
  box-sizing: border-box;
}

.grade-hero-card {
  background: #ffffff;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  padding: 18px 20px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 16px;
  box-shadow: var(--shadow-sm);
  position: relative;
  overflow: hidden;
  gap: 16px;
}

.grade-hero-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 5px;
  height: 100%;
  background: var(--accent-current);
}

.grade-hero-tag {
  display: inline-block;
  font-family: var(--font-display);
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--accent-current);
  background: var(--accent-current-light);
  padding: 3px 8px;
  border-radius: 100px;
  margin-bottom: 6px;
}

.grade-hero-card h2 {
  font-size: 1.25rem;
  font-weight: 800;
  color: var(--text-primary);
  margin-bottom: 3px;
  line-height: 1.3;
}

.grade-hero-card p {
  font-size: 0.86rem;
  color: var(--text-secondary);
}

.grade-hero-meta {
  display: flex;
  gap: 10px;
  flex-shrink: 0;
}

.hero-metric {
  background: var(--bg-subtle);
  padding: 8px 12px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  min-width: 68px;
  text-align: center;
}

.metric-num {
  font-family: var(--font-display);
  font-size: 1.15rem;
  font-weight: 800;
  color: var(--text-primary);
  line-height: 1.2;
}

.metric-lbl {
  font-size: 0.68rem;
  color: var(--text-muted);
  font-weight: 600;
  text-transform: uppercase;
}

/* =============================================================================
   TOPICS SECTION (Grid Layout - NO Horizontal Scroll!)
   ============================================================================= */
.topic-tabs-section {
  margin-bottom: 16px;
}

.topic-tabs-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 10px;
  flex-wrap: wrap;
  gap: 8px;
}

.section-label {
  font-family: var(--font-display);
  font-size: 0.86rem;
  font-weight: 700;
  color: var(--text-secondary);
}

.mode-toggle-group {
  display: flex;
  background: #ffffff;
  border: 1px solid var(--border-color);
  padding: 3px;
  border-radius: var(--radius-sm);
  gap: 3px;
}

.mode-btn {
  padding: 6px 12px;
  min-height: 36px;
  border-radius: var(--radius-xs);
  border: none;
  background: transparent;
  font-family: var(--font-body);
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition-fast);
  white-space: nowrap;
  touch-action: manipulation;
}

.mode-btn:hover {
  color: var(--text-primary);
  background: var(--bg-subtle);
}

.mode-btn.active {
  background: var(--accent-current);
  color: #ffffff;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
}

/* Topics Grid - Fully fits on screen, no sliding right! */
.topic-tabs-wrapper {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 8px;
  width: 100%;
  box-sizing: border-box;
}

.topic-tab-card {
  background: #ffffff;
  border: 1.5px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: 10px 12px;
  cursor: pointer;
  transition: all var(--transition-fast);
  display: flex;
  align-items: center;
  gap: 10px;
  touch-action: manipulation;
  width: 100%;
  max-width: 100%;
  box-sizing: border-box;
  overflow: hidden;
}

.topic-tab-card:hover {
  border-color: #cbd5e1;
  box-shadow: var(--shadow-sm);
}

.topic-tab-card:active {
  transform: scale(0.98);
}

.topic-tab-card.active {
  border-color: var(--accent-current);
  background: var(--accent-current-light);
  box-shadow: 0 0 0 1px var(--accent-current);
}

.topic-tab-icon {
  font-size: 1.25rem;
  width: 34px;
  height: 34px;
  border-radius: 8px;
  background: var(--bg-subtle);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.topic-tab-info {
  min-width: 0;
  flex: 1;
  overflow: hidden;
}

.topic-tab-title {
  font-family: var(--font-display);
  font-size: 0.84rem;
  font-weight: 700;
  color: var(--text-primary);
  line-height: 1.25;
  white-space: normal;
  word-break: break-word;
}

.topic-tab-badge {
  font-size: 0.7rem;
  color: var(--text-muted);
  font-weight: 500;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

/* =============================================================================
   THEORY CARD & FORMULAS
   ============================================================================= */
.topic-theory-card {
  background: #ffffff;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 16px 18px;
  margin-bottom: 18px;
  box-shadow: var(--shadow-sm);
  transition: all var(--transition-smooth);
}

.theory-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  border-bottom: 1px solid var(--border-color);
  padding-bottom: 12px;
  margin-bottom: 14px;
  gap: 10px;
  cursor: pointer;
  user-select: none;
}

.theory-title-group {
  display: flex;
  align-items: center;
  gap: 10px;
  min-width: 0;
}

.theory-icon {
  font-size: 1.3rem;
  flex-shrink: 0;
}

.theory-title-wrapper {
  min-width: 0;
}

.theory-title-group h3 {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--text-primary);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.theory-badge {
  font-size: 0.72rem;
  font-weight: 600;
  color: var(--text-muted);
}

.theory-summary-text {
  font-size: 0.88rem;
  color: var(--text-secondary);
  margin-bottom: 12px;
  line-height: 1.55;
}

.formula-box {
  background: #f8fafc;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: 12px 14px;
  font-size: 0.9rem;
  color: var(--text-primary);
}

/* =============================================================================
   VIEW SECTIONS (Learn, Quiz, Generator)
   ============================================================================= */
.view-section {
  display: none;
}
.view-section.active {
  display: block;
  animation: fadeIn 0.25s ease;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(6px); }
  to { opacity: 1; transform: translateY(0); }
}

.exercises-header {
  margin-bottom: 14px;
}

.exercises-header h3 {
  font-size: 1.1rem;
  font-weight: 800;
  color: var(--text-primary);
}

.exercises-subtitle {
  font-size: 0.82rem;
  color: var(--text-muted);
}

.exercises-list {
  display: flex;
  flex-direction: column;
  gap: 14px;
}

/* Exercise Card */
.exercise-card {
  background: #ffffff;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast), transform var(--transition-fast);
  scroll-margin-top: 80px;
  scroll-margin-bottom: 90px;
  width: 100%;
  max-width: 100%;
  box-sizing: border-box;
}

.exercise-card:hover {
  border-color: #cbd5e1;
}

.exercise-card.expanded {
  border-color: #cbd5e1;
  box-shadow: 0 4px 16px -2px rgba(15, 23, 42, 0.08);
}

.card-top {
  padding: 14px 16px;
  display: flex;
  align-items: center;
  gap: 12px;
  cursor: pointer;
  user-select: none;
  background: #ffffff;
  min-height: 56px;
  touch-action: manipulation;
  transition: background var(--transition-fast), transform 0.1s ease;
  width: 100%;
  box-sizing: border-box;
}

.card-top:hover {
  background: var(--bg-subtle);
}

.card-top:active {
  background: #f1f5f9;
  transform: scale(0.995);
}

.ex-number {
  font-family: var(--font-display);
  width: 32px;
  height: 32px;
  border-radius: var(--radius-xs);
  background: var(--accent-current);
  color: #ffffff;
  font-weight: 800;
  font-size: 0.9rem;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.card-info {
  flex: 1;
  min-width: 0;
}

.card-title {
  font-family: var(--font-display);
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 2px;
  line-height: 1.3;
}

.card-meta {
  display: flex;
  align-items: center;
  gap: 6px;
  flex-wrap: wrap;
}

.badge {
  font-size: 0.7rem;
  font-weight: 600;
  padding: 2px 7px;
  border-radius: 100px;
}

.badge-green { background: #dcfce7; color: #15803d; }
.badge-yellow { background: #fef9c3; color: #a16207; }
.badge-orange { background: #ffedd5; color: #c2410c; }
.badge-red { background: #fee2e2; color: #b91c1c; }

.card-chevron {
  font-size: 0.8rem;
  color: var(--text-muted);
  transition: transform var(--transition-fast);
  padding: 4px;
  flex-shrink: 0;
}

.exercise-card.expanded .card-chevron {
  transform: rotate(180deg);
}

.card-body {
  display: none;
  border-top: 1px solid var(--border-color);
  padding: 16px;
  background: #fafbfc;
}

.exercise-card.expanded .card-body {
  display: block;
}

.statement-box {
  background: #ffffff;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: 14px 16px;
  margin-bottom: 16px;
  font-size: 0.95rem;
  color: var(--text-primary);
  line-height: 1.6;
}

.hint-pill {
  margin-top: 8px;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 0.8rem;
  color: #b45309;
  background: #fffbeb;
  padding: 4px 10px;
  border-radius: 100px;
  border: 1px solid #fde68a;
  max-width: 100%;
}

/* Step Navigation Controls */
.step-controls {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 12px;
  flex-wrap: wrap;
  gap: 10px;
}

.step-counter {
  font-family: var(--font-display);
  font-size: 0.84rem;
  font-weight: 700;
  color: var(--text-secondary);
}

.control-buttons {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
}

.progress-track {
  width: 100%;
  height: 4px;
  background: #e2e8f0;
  border-radius: 2px;
  margin-bottom: 16px;
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: var(--accent-current);
  width: 0%;
  transition: width var(--transition-fast);
}

.steps-timeline {
  display: flex;
  flex-direction: column;
  gap: 10px;
  margin-bottom: 16px;
}

.step-item {
  display: none;
  background: #ffffff;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: 12px 14px;
  gap: 12px;
  align-items: flex-start;
  transition: all var(--transition-fast);
}

.step-item.visible {
  display: flex;
}

.step-item.active {
  border-color: var(--accent-current);
  background: var(--bg-active-step);
  box-shadow: 0 0 0 1px var(--accent-current);
}

.step-item.dimmed {
  opacity: 0.8;
}

.step-marker {
  font-family: var(--font-display);
  width: 24px;
  height: 24px;
  border-radius: 50%;
  background: var(--bg-subtle);
  border: 1px solid var(--border-color);
  font-size: 0.78rem;
  font-weight: 700;
  color: var(--text-secondary);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  margin-top: 2px;
}

.step-item.active .step-marker {
  background: var(--accent-current);
  color: #ffffff;
  border-color: var(--accent-current);
}

.step-content {
  flex: 1;
  font-size: 0.9rem;
  color: var(--text-primary);
  line-height: 1.6;
  min-width: 0;
}

/* Final Answer Banner */
.final-answer {
  display: none;
  background: #f0fdf4;
  border: 1px solid #bbf7d0;
  border-radius: var(--radius-sm);
  padding: 14px 16px;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
}

.final-answer.visible {
  display: flex;
  animation: celebrate 0.35s ease;
}

@keyframes celebrate {
  0% { transform: scale(0.98); opacity: 0.5; }
  50% { transform: scale(1.01); }
  100% { transform: scale(1); opacity: 1; }
}

.final-label {
  font-family: var(--font-display);
  font-weight: 700;
  color: #166534;
  font-size: 0.92rem;
}

.final-math {
  font-family: var(--font-mono);
  font-size: 1rem;
  color: #14532d;
}

/* =============================================================================
   QUIZ & AUTOEVALUACION
   ============================================================================= */
.quiz-hero {
  background: #ffffff;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 16px 18px;
  margin-bottom: 16px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 14px;
}

.quiz-hero-text h3 {
  font-size: 1.05rem;
  font-weight: 800;
  color: var(--text-primary);
  margin-bottom: 3px;
}

.quiz-hero-text p {
  font-size: 0.82rem;
  color: var(--text-muted);
}

.quiz-score-badge {
  background: var(--bg-subtle);
  border: 1px solid var(--border-color);
  padding: 8px 14px;
  border-radius: var(--radius-sm);
  text-align: center;
  flex-shrink: 0;
}

.score-label {
  display: block;
  font-size: 0.68rem;
  color: var(--text-muted);
  font-weight: 600;
  text-transform: uppercase;
}

.score-value {
  font-family: var(--font-display);
  font-size: 1.15rem;
  font-weight: 800;
  color: var(--accent-current);
}

.quiz-card {
  background: #ffffff;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 16px 18px;
  margin-bottom: 16px;
  box-shadow: var(--shadow-sm);
}

.quiz-question-title {
  font-family: var(--font-display);
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 10px;
  line-height: 1.5;
}

.quiz-options-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 8px;
  margin: 14px 0;
}

.quiz-option-btn {
  padding: 12px 14px;
  min-height: 48px;
  border-radius: var(--radius-sm);
  background: #ffffff;
  border: 1px solid var(--border-color);
  font-family: var(--font-body);
  font-size: 0.9rem;
  text-align: left;
  cursor: pointer;
  color: var(--text-primary);
  transition: all var(--transition-fast);
  display: flex;
  align-items: center;
  gap: 10px;
  touch-action: manipulation;
}

.quiz-option-btn:hover {
  background: var(--bg-subtle);
  border-color: #cbd5e1;
}

.quiz-option-btn:active {
  background: #e2e8f0;
}

.quiz-option-btn.selected {
  border-color: var(--accent-current);
  background: var(--accent-current-light);
}

.quiz-option-btn.correct {
  border-color: #22c55e !important;
  background: #dcfce7 !important;
  color: #166534 !important;
}

.quiz-option-btn.wrong {
  border-color: #ef4444 !important;
  background: #fee2e2 !important;
  color: #991b1b !important;
}

.quiz-feedback {
  display: none;
  margin-top: 12px;
  padding: 12px 14px;
  border-radius: var(--radius-sm);
  font-size: 0.88rem;
}

.quiz-feedback.visible { display: block; }
.quiz-feedback.success { background: #f0fdf4; border: 1px solid #bbf7d0; color: #166534; }
.quiz-feedback.error { background: #fef2f2; border: 1px solid #fecaca; color: #991b1b; }

/* =============================================================================
   GENERATOR VIEW
   ============================================================================= */
.generator-card {
  background: #ffffff;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 18px 20px;
  box-shadow: var(--shadow-sm);
}

.generator-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  border-bottom: 1px solid var(--border-color);
  padding-bottom: 14px;
  margin-bottom: 16px;
  flex-wrap: wrap;
  gap: 12px;
}

.generator-title-group {
  display: flex;
  align-items: center;
  gap: 12px;
  min-width: 0;
}

.generator-icon {
  font-size: 1.4rem;
  width: 40px;
  height: 40px;
  border-radius: var(--radius-sm);
  background: var(--accent-current-light);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.generator-title-group h3 {
  font-size: 1.05rem;
  font-weight: 800;
  color: var(--text-primary);
}

.generator-title-group p {
  font-size: 0.82rem;
  color: var(--text-muted);
}

.btn-generate {
  min-height: 44px;
  padding: 10px 18px;
}

/* =============================================================================
   MODAL & PRINTABLE GUIDE
   ============================================================================= */
.modal-overlay {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(15, 23, 42, 0.5);
  backdrop-filter: blur(4px);
  z-index: 2000;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 16px;
}

.modal-card {
  background: #ffffff;
  border-radius: var(--radius-md);
  width: 100%;
  max-width: 720px;
  max-height: 85vh;
  display: flex;
  flex-direction: column;
  box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.1);
  border: 1px solid var(--border-color);
}

.modal-header {
  padding: 14px 18px;
  border-bottom: 1px solid var(--border-color);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.modal-header h3 {
  font-size: 1.05rem;
  font-weight: 800;
}

.modal-close-btn {
  background: none;
  border: none;
  font-size: 1.2rem;
  cursor: pointer;
  color: var(--text-muted);
  padding: 6px 10px;
  border-radius: 6px;
}
.modal-close-btn:hover { background: var(--bg-subtle); color: var(--text-primary); }

.modal-body {
  padding: 18px;
  overflow-y: auto;
  font-size: 0.9rem;
  line-height: 1.6;
}

.modal-footer {
  padding: 12px 18px;
  border-top: 1px solid var(--border-color);
  display: flex;
  justify-content: flex-end;
  gap: 8px;
}

/* =============================================================================
   MOBILE BOTTOM NAVIGATION (Fixed at bottom on phones)
   ============================================================================= */
.mobile-bottom-nav {
  display: none;
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  background: rgba(255, 255, 255, 0.96);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-top: 1px solid var(--border-color);
  z-index: 1000;
  padding: 6px 8px calc(6px + env(safe-area-inset-bottom));
  box-shadow: 0 -2px 12px rgba(15, 23, 42, 0.06);
  justify-content: space-around;
  align-items: center;
}

.mobile-nav-item {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 2px;
  background: transparent;
  border: none;
  padding: 6px 10px;
  border-radius: var(--radius-xs);
  color: var(--text-muted);
  cursor: pointer;
  flex: 1;
  min-height: 48px;
  touch-action: manipulation;
  transition: all var(--transition-fast);
}

.mobile-nav-item.active {
  color: var(--accent-current);
}

.mobile-nav-icon {
  font-size: 1.25rem;
  line-height: 1;
}

.mobile-nav-label {
  font-family: var(--font-display);
  font-size: 0.72rem;
  font-weight: 700;
}

/* Search Banner */
.search-results-banner {
  background: #eff6ff;
  border: 1px solid #bfdbfe;
  padding: 8px 14px;
  border-radius: var(--radius-sm);
  margin-bottom: 16px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 0.84rem;
  color: #1e40af;
  flex-wrap: wrap;
  gap: 6px;
}

/* Footer */
.site-footer {
  text-align: center;
  padding: 24px 16px;
  border-top: 1px solid var(--border-color);
  background: #ffffff;
  color: var(--text-secondary);
  font-size: 0.82rem;
}

.footer-sub {
  font-size: 0.74rem;
  color: var(--text-muted);
  margin-top: 3px;
}

/* =============================================================================
   RESPONSIVE MEDIA QUERIES (Zero Horizontal Scrolling on Mobile!)
   ============================================================================= */

@media (max-width: 900px) {
  .quiz-options-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 768px) {
  /* Show Mobile Bottom Bar */
  .mobile-bottom-nav {
    display: flex;
  }
  
  /* Hide duplicate desktop mode toggle in topic header */
  .mode-toggle-group {
    display: none;
  }

  .site-header h1 {
    font-size: 1.02rem;
  }

  .header-content {
    flex-wrap: wrap;
    padding: 8px 12px;
  }

  .header-actions {
    width: 100%;
    justify-content: space-between;
    margin-top: 4px;
    gap: 6px;
  }

  .search-box {
    flex: 1;
    width: auto;
    min-height: 36px;
  }

  .search-box:focus-within {
    width: auto;
  }

  .btn-text-hide-mobile {
    display: none;
  }

  .stat-pill .stat-label {
    display: none;
  }

  /* Grades: 3 columns x 2 rows (fits 100% on screen, 0 scrolling!) */
  .grade-nav {
    grid-template-columns: repeat(3, 1fr);
    padding: 4px 12px 8px;
    gap: 6px;
  }

  .grade-btn {
    padding: 6px 8px;
    min-height: 42px;
    gap: 6px;
  }

  .grade-badge {
    width: 26px;
    height: 26px;
    font-size: 0.78rem;
  }

  .grade-name {
    font-size: 0.78rem;
  }

  .grade-btn-info .grade-desc {
    display: none;
  }

  .container {
    padding: 10px 12px 70px;
  }

  .grade-hero-card {
    flex-direction: column;
    align-items: flex-start;
    gap: 12px;
    padding: 14px 14px;
  }

  .grade-hero-meta {
    width: 100%;
    justify-content: flex-start;
  }

  .hero-metric {
    flex: 1;
    padding: 6px 8px;
  }

  /* Topics: 2 columns on tablet/mobile (fits 100% on screen, 0 scrolling!) */
  .topic-tabs-wrapper {
    grid-template-columns: 1fr 1fr;
    gap: 6px;
  }

  .topic-tab-card {
    padding: 8px 10px;
    gap: 8px;
  }

  .topic-tab-icon {
    width: 30px;
    height: 30px;
    font-size: 1.1rem;
  }

  .topic-tab-title {
    font-size: 0.78rem;
  }

  .topic-tab-badge {
    font-size: 0.68rem;
  }

  /* Steps Control: 2x2 touch button grid */
  .step-controls {
    flex-direction: column;
    align-items: stretch;
    gap: 8px;
  }

  .control-buttons {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 6px;
  }

  .control-buttons .btn {
    width: 100%;
    min-height: 44px;
    font-size: 0.84rem;
  }

  .generator-header {
    flex-direction: column;
    align-items: stretch;
  }

  .btn-generate {
    width: 100%;
  }

  .modal-card {
    max-height: 95vh;
    border-radius: var(--radius-sm);
  }

  .modal-footer {
    flex-direction: column-reverse;
  }

  .modal-footer .btn {
    width: 100%;
    min-height: 44px;
  }
}

@media (max-width: 480px) {
  .topic-tabs-wrapper {
    grid-template-columns: 1fr;
  }

  .card-top {
    padding: 12px 12px;
    min-height: 52px;
  }

  .card-body {
    padding: 12px 10px;
  }

  .statement-box {
    padding: 12px 12px;
    font-size: 0.9rem;
  }

  .step-item {
    padding: 10px 12px;
    gap: 10px;
  }

  .step-content {
    font-size: 0.88rem;
  }
}

/* =============================================================================
   PRINT STYLESHEET
   ============================================================================= */
@media print {
  body {
    background: #ffffff !important;
    color: #000000 !important;
    padding-bottom: 0 !important;
  }
  .site-header, .mode-toggle-group, .step-controls, .site-footer, .btn, .mobile-bottom-nav {
    display: none !important;
  }
  
  /* If printing with modal open */
  .modal-overlay {
    position: static !important;
    background: none !important;
    padding: 0 !important;
    display: block !important;
  }
  .modal-card {
    max-width: 100% !important;
    max-height: none !important;
    border: none !important;
    box-shadow: none !important;
    width: 100% !important;
  }
  .modal-header, .modal-footer {
    display: none !important;
  }
  .modal-body {
    padding: 0 !important;
    overflow: visible !important;
  }

  .exercise-card {
    break-inside: avoid;
    box-shadow: none;
    border: 1px solid #000;
    margin-bottom: 16px;
  }
  .card-body {
    display: block !important;
  }
  .step-item {
    display: flex !important;
  }
  .final-answer {
    display: flex !important;
  }
}