/* ==========================================================================
   LinAlgLab Interactive - Complete Design System & Styling
   ========================================================================== */

/* 1. CSS Custom Properties / Design Tokens */
:root {
  /* Color Palette - Dark Mode Default */
  --bg-primary: #0f172a;
  --bg-secondary: #1e293b;
  --bg-card: rgba(30, 41, 59, 0.75);
  --bg-card-hover: rgba(51, 65, 85, 0.85);
  --bg-glass: rgba(15, 23, 42, 0.88);

  --text-main: #f8fafc;
  --text-muted: #94a3b8;
  --text-dim: #64748b;

  --accent-cyan: #06b6d4;
  --accent-purple: #8b5cf6;
  --accent-pink: #ec4899;
  --accent-emerald: #10b981;
  --accent-amber: #f59e0b;
  --accent-rose: #f43f5e;
  --accent-blue: #3b82f6;

  --border-color: rgba(255, 255, 255, 0.08);
  --border-accent: rgba(6, 182, 212, 0.35);

  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 20px;

  --shadow-subtle: 0 4px 20px rgba(0, 0, 0, 0.25);
  --shadow-glow: 0 0 25px rgba(6, 182, 212, 0.18);

  --font-sans: 'Inter', system-ui, -apple-system, sans-serif;
  --font-mono: 'Fira Code', monospace;
}

/* Light Mode Overrides */
body.light-mode {
  --bg-primary: #f8fafc;
  --bg-secondary: #ffffff;
  --bg-card: rgba(255, 255, 255, 0.95);
  --bg-card-hover: rgba(241, 245, 249, 1);
  --bg-glass: rgba(255, 255, 255, 0.92);

  --text-main: #0f172a;
  --text-muted: #475569;
  --text-dim: #94a3b8;

  --border-color: rgba(0, 0, 0, 0.1);
  --border-accent: rgba(6, 182, 212, 0.45);

  --shadow-subtle: 0 4px 20px rgba(0, 0, 0, 0.06);
  --shadow-glow: 0 0 25px rgba(6, 182, 212, 0.12);
}

/* 2. Global Reset & Base Styles */
* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: var(--font-sans);
  background-color: var(--bg-primary);
  color: var(--text-main);
  line-height: 1.6;
  min-height: 100vh;
  transition: background-color 0.3s ease, color 0.3s ease;
  overflow-x: hidden;
}

/* Hide Phonetics when toggled off */
body:not(.show-ipa) .ipa-wrapper {
  display: none !important;
}

/* 3. Navigation Header */
.navbar {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--bg-glass);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border-color);
  padding: 0.5rem 1.25rem;
}

.nav-container {
  max-width: 1600px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  flex: 0 0 auto;
  min-width: 0;
}

.brand-icon {
  width: 42px;
  height: 42px;
  background: linear-gradient(135deg, var(--accent-cyan), var(--accent-purple));
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  color: #fff;
  box-shadow: var(--shadow-glow);
}

.brand-text {
  display: flex;
  flex-direction: column;
}

.brand-title {
  font-size: 1.15rem;
  font-weight: 700;
  background: linear-gradient(90deg, #fff, var(--text-muted));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  white-space: nowrap;
}

body.light-mode .brand-title {
  background: linear-gradient(90deg, #0f172a, #334155);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.brand-subtitle {
  font-size: 0.75rem;
  color: var(--text-muted);
  display: none;
  white-space: nowrap;
}

.nav-track {
  flex: 1 1 auto;
  min-width: 0;
  display: grid;
  grid-template-columns: 32px minmax(0, 1fr) 32px;
  align-items: center;
  gap: 0.35rem;
}

.nav-viewport {
  min-width: 0;
  overflow-x: auto;
  scroll-behavior: smooth;
  scrollbar-width: none;
}

.nav-viewport::-webkit-scrollbar { display: none; }

.nav-menu {
  display: grid;
  grid-auto-flow: column;
  grid-auto-columns: calc((100% - 1.5rem) / 4);
  gap: 0.5rem;
  background: var(--bg-secondary);
  padding: 0.3rem;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  width: 100%;
}

.nav-link {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  justify-content: center;
  min-height: 52px;
  padding: 0.5rem 0.55rem;
  border: none;
  background: transparent;
  color: var(--text-muted);
  font-size: 0.85rem;
  font-weight: 500;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all 0.2s ease;
}

.nav-scroll-btn {
  width: 32px;
  height: 36px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  background: var(--bg-secondary);
  color: var(--text-muted);
  cursor: pointer;
  transition: all 0.2s ease;
}

.nav-scroll-btn:hover:not(:disabled) { color: var(--accent-cyan); border-color: var(--accent-cyan); }
.nav-scroll-btn:disabled { opacity: 0.35; cursor: not-allowed; }
.nav-scroll-btn i { width: 17px; height: 17px; }

.nav-link:hover {
  color: var(--text-main);
  background: rgba(255, 255, 255, 0.05);
}

.nav-link.active {
  background: linear-gradient(135deg, var(--accent-cyan), var(--accent-blue));
  color: #ffffff;
  font-weight: 600;
  box-shadow: 0 4px 12px rgba(6, 182, 212, 0.3);
}

.nav-controls {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  flex: 0 0 auto;
}

.theme-btn, .phonetic-btn, .lang-btn {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.5rem 0.85rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  background: var(--bg-secondary);
  color: var(--text-main);
  font-size: 0.8rem;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.2s ease;
}

.theme-btn:hover, .phonetic-btn:hover, .lang-btn:hover {
  border-color: var(--accent-cyan);
}

.phonetic-btn.active {
  border-color: var(--accent-emerald);
  color: var(--accent-emerald);
}

.theme-btn {
  color: var(--accent-amber);
}

/* 4. Hero Banner */
.hero-banner {
  position: relative;
  background: radial-gradient(circle at 50% 0%, rgba(6, 182, 212, 0.15), transparent 70%), var(--bg-primary);
  padding: 2.8rem 1.5rem;
  border-bottom: 1px solid var(--border-color);
  overflow: hidden;
}

.hero-grid-bg {
  position: absolute;
  top: 0; left: 0; right: 0; bottom: 0;
  background-image: 
    linear-gradient(rgba(6, 182, 212, 0.04) 1px, transparent 1px),
    linear-gradient(90deg, rgba(6, 182, 212, 0.04) 1px, transparent 1px);
  background-size: 30px 30px;
  animation: gridMove 20s linear infinite;
  pointer-events: none;
}

@keyframes gridMove {
  0% { background-position: 0 0; }
  100% { background-position: 30px 30px; }
}

.hero-content {
  position: relative;
  z-index: 2;
  max-width: 1200px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 2rem;
  flex-wrap: wrap;
}

.hero-text-block {
  flex: 1;
  min-width: 300px;
}

.hero-text-block h1 {
  font-size: 2.1rem;
  font-weight: 700;
  line-height: 1.25;
  margin-bottom: 0.75rem;
  background: linear-gradient(135deg, #ffffff 0%, var(--accent-cyan) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

body.light-mode .hero-text-block h1 {
  background: linear-gradient(135deg, #0f172a 0%, var(--accent-blue) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.hero-text-block p {
  color: var(--text-muted);
  font-size: 0.95rem;
  max-width: 720px;
}

.hero-stats {
  display: flex;
  gap: 1rem;
}

.stat-card {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  padding: 0.9rem 1.4rem;
  border-radius: var(--radius-md);
  display: flex;
  flex-direction: column;
  align-items: center;
  min-width: 105px;
  box-shadow: var(--shadow-subtle);
  transition: transform 0.2s ease;
}

.stat-card:hover {
  transform: translateY(-3px);
  border-color: var(--border-accent);
}

.stat-num {
  font-size: 1.6rem;
  font-weight: 700;
  color: var(--accent-cyan);
}

.stat-label {
  font-size: 0.75rem;
  color: var(--text-muted);
}

/* 5. Main Layout & Tab Panels */
.main-container {
  max-width: 1320px;
  margin: 2rem auto;
  padding: 0 1.5rem;
}

.tab-panel {
  display: none;
  animation: fadeIn 0.35s ease;
}

.tab-panel.active {
  display: block;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

.section-header {
  margin-bottom: 1.8rem;
}

.badge {
  display: inline-block;
  padding: 0.25rem 0.75rem;
  background: rgba(6, 182, 212, 0.15);
  color: var(--accent-cyan);
  border: 1px solid var(--border-accent);
  border-radius: 50px;
  font-size: 0.75rem;
  font-weight: 600;
  margin-bottom: 0.5rem;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.section-header h2 {
  font-size: 1.65rem;
  font-weight: 700;
  margin-bottom: 0.4rem;
}

.section-header p {
  color: var(--text-muted);
  font-size: 0.95rem;
}

/* 6. Cards Grid & Theory Cards */
.cards-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 1.5rem;
  margin-bottom: 2rem;
}

.card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.4rem;
  backdrop-filter: blur(10px);
  transition: transform 0.2s ease, border-color 0.2s ease, box-shadow 0.2s ease;
}

.card:hover {
  transform: translateY(-2px);
  border-color: var(--border-accent);
  box-shadow: var(--shadow-glow);
}

.card-header {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  margin-bottom: 1rem;
  padding-bottom: 0.6rem;
  border-bottom: 1px solid var(--border-color);
}

.card-icon {
  color: var(--accent-cyan);
}

.card-header h3 {
  font-size: 1.1rem;
  font-weight: 600;
}

.concept-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.concept-list li {
  font-size: 0.9rem;
}

.concept-list strong {
  color: var(--text-main);
}

.ipa-wrapper {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  margin: 0 0.3rem;
}

.ipa-tag {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  background: rgba(139, 92, 246, 0.15);
  color: var(--accent-purple);
  padding: 0.1rem 0.4rem;
  border-radius: 4px;
}

.audio-btn {
  background: transparent;
  border: none;
  color: var(--accent-cyan);
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.15rem;
  border-radius: 4px;
  transition: background 0.2s;
}

.audio-btn:hover {
  background: rgba(6, 182, 212, 0.2);
}

.math-expr {
  margin-top: 0.4rem;
  padding: 0.4rem 0.8rem;
  background: var(--bg-secondary);
  border-radius: var(--radius-sm);
  overflow-x: auto;
  font-size: 0.95rem;
}

/* 7. Interactive Canvas Widget */
.interactive-widget {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  margin-bottom: 2rem;
  box-shadow: var(--shadow-subtle);
}

.widget-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 1rem;
  margin-bottom: 1.2rem;
  padding-bottom: 1rem;
  border-bottom: 1px solid var(--border-color);
  flex-wrap: wrap;
}

.widget-header h3 {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--accent-cyan);
}

.widget-header p {
  font-size: 0.85rem;
  color: var(--text-muted);
}

.widget-badge {
  padding: 0.4rem 0.9rem;
  background: rgba(16, 185, 129, 0.15);
  border: 1px solid rgba(16, 185, 129, 0.4);
  color: var(--accent-emerald);
  border-radius: var(--radius-sm);
  font-size: 0.8rem;
  font-weight: 600;
}

.widget-body {
  display: grid;
  grid-template-columns: 320px 1fr;
  gap: 1.5rem;
}

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

/* Controls Panel & Color-Coded Control Groups */
.controls-panel {
  display: flex;
  flex-direction: column;
  gap: 1.2rem;
  background: var(--bg-primary);
  padding: 1.2rem;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  box-shadow: var(--shadow-subtle);
}

body.light-mode .controls-panel {
  background: #ffffff;
  border-color: rgba(0, 0, 0, 0.08);
  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.04);
}

.control-group {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  padding: 0.6rem 0.8rem;
  border-radius: var(--radius-sm);
  border-left: 3px solid var(--border-color);
  background: rgba(255, 255, 255, 0.02);
  transition: all 0.2s ease;
}

.control-group.vec-u-group {
  border-left-color: var(--accent-cyan);
  background: rgba(6, 182, 212, 0.04);
}

.control-group.vec-v-group {
  border-left-color: var(--accent-purple);
  background: rgba(139, 92, 246, 0.04);
}

.control-group.probe-group {
  border-left-color: var(--accent-pink);
  background: rgba(236, 72, 153, 0.04);
}

.control-group.lincomb-group {
  border-left-color: var(--accent-emerald);
  background: rgba(16, 185, 129, 0.04);
}

.control-label {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--text-main);
}

.color-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  display: inline-block;
}

.color-dot.cyan { background: var(--accent-cyan); box-shadow: 0 0 6px var(--accent-cyan); }
.color-dot.purple { background: var(--accent-purple); box-shadow: 0 0 6px var(--accent-purple); }
.color-dot.pink { background: var(--accent-pink); box-shadow: 0 0 6px var(--accent-pink); }
.color-dot.blue { background: var(--accent-blue); box-shadow: 0 0 6px var(--accent-blue); }
.color-dot.amber { background: var(--accent-amber); box-shadow: 0 0 6px var(--accent-amber); }

.slider-wrapper {
  display: flex;
  align-items: center;
  gap: 0.6rem;
}

.slider-pair {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.8rem;
  color: var(--text-muted);
}

.slider-pair input[type="range"] {
  flex: 1;
}

input[type="range"] {
  -webkit-appearance: none;
  width: 100%;
  height: 6px;
  background: var(--bg-secondary);
  border-radius: 3px;
  outline: none;
}

body.light-mode input[type="range"] {
  background: #e2e8f0;
}

input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  width: 16px;
  height: 16px;
  border-radius: 50%;
  background: var(--accent-cyan);
  cursor: pointer;
  box-shadow: 0 0 8px rgba(6, 182, 212, 0.6);
  transition: transform 0.1s ease;
}

input[type="range"]::-webkit-slider-thumb:hover {
  transform: scale(1.2);
}

.value-badge {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  font-weight: 600;
  padding: 0.15rem 0.5rem;
  border-radius: 4px;
  min-width: 42px;
  text-align: center;
}

.value-badge.cyan { background: rgba(6, 182, 212, 0.15); color: var(--accent-cyan); }
.value-badge.purple { background: rgba(139, 92, 246, 0.15); color: var(--accent-purple); }
.value-badge.pink { background: rgba(236, 72, 153, 0.15); color: var(--accent-pink); }
.value-badge.emerald { background: rgba(16, 185, 129, 0.15); color: var(--accent-emerald); }
.value-badge.blue { background: rgba(59, 130, 246, 0.15); color: var(--accent-blue); }
.value-badge.amber { background: rgba(245, 158, 11, 0.15); color: var(--accent-amber); }

/* Mathematical Matrix Container Redesign (Option A + B) */
.matrix-input-grid {
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}

.matrix-box {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.6rem;
  padding: 0.75rem 1rem;
  background: rgba(6, 182, 212, 0.04);
  border-radius: var(--radius-sm);
  position: relative;
  box-sizing: border-box;
}

.matrix-box.matrix-box-secondary {
  background: rgba(139, 92, 246, 0.06);
}

.matrix-box.matrix-box-secondary::before,
.matrix-box.matrix-box-secondary::after {
  border-color: var(--accent-purple);
}

.composition-order-toggle {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.55rem;
}

.composition-preset-grid {
  grid-template-columns: 1fr 1fr;
}

.composition-result {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
  padding: 0.75rem 0.9rem;
  border-radius: var(--radius-sm);
  background: rgba(16, 185, 129, 0.1);
  border: 1px solid rgba(16, 185, 129, 0.3);
  color: var(--text-main);
  font-size: 0.85rem;
}

.composition-result output {
  color: var(--accent-emerald);
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
  font-size: 0.9rem;
  overflow-wrap: anywhere;
}

.composition-widget .widget-body {
  grid-template-columns: 400px minmax(0, 1fr);
  align-items: flex-start;
  margin-bottom: 1.25rem;
}

.composition-widget .controls-panel {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  align-content: start;
  gap: 0.9rem;
}

.composition-widget .controls-panel > .control-group,
.composition-widget .controls-panel > .composition-result,
.composition-widget .controls-panel > .rule-callout {
  grid-column: 1 / -1;
}

.composition-widget .chart-panel {
  align-self: flex-start;
  align-items: flex-start;
  justify-content: flex-start;
}

.composition-widget .composition-canvas-wrapper {
  width: 100%;
  max-width: 720px;
}

.composition-derivation {
  display: flex;
  flex-direction: column;
  gap: 0.7rem;
  padding: 0.9rem;
  margin-top: 0.25rem;
  border: 1px solid rgba(6, 182, 212, 0.3);
  border-radius: var(--radius-sm);
  background: rgba(6, 182, 212, 0.05);
}

.composition-derivation h4 {
  color: var(--accent-cyan);
  font-size: 0.95rem;
}

.composition-derivation-hint,
.composition-basis-link {
  margin: 0;
  color: var(--text-muted);
  font-size: 0.8rem;
  line-height: 1.45;
}

.composition-equation {
  color: var(--accent-emerald);
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
  font-weight: 700;
  font-size: 0.9rem;
}

.composition-matrix-flow {
  display: grid;
  grid-template-columns: 1fr auto 1fr auto 1fr;
  align-items: center;
  gap: 0.45rem;
}

.composition-matrix-card {
  min-width: 0;
  padding: 0.5rem;
  border: 1px solid var(--border-color);
  border-radius: 0.35rem;
  background: var(--bg-primary);
}

.composition-matrix-card strong {
  display: block;
  margin-bottom: 0.25rem;
  color: var(--text-muted);
  font-size: 0.72rem;
}

.composition-matrix-value {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.16rem 0.35rem;
  padding: 0.15rem 0.35rem;
  border-left: 2px solid var(--accent-cyan);
  border-right: 2px solid var(--accent-cyan);
  color: var(--text-main);
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
  font-size: 0.78rem;
  text-align: center;
}

.composition-matrix-card.result .composition-matrix-value {
  border-color: var(--accent-emerald);
  color: var(--accent-emerald);
}

.composition-matrix-operator {
  color: var(--accent-purple);
  font-size: 1.15rem;
  font-weight: 700;
}

.composition-entry-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 0.5rem;
}

.composition-entry {
  padding: 0.6rem;
  border-radius: 0.35rem;
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
  font-size: 0.76rem;
  line-height: 1.5;
}

.composition-entry strong {
  color: var(--accent-cyan);
}

.composition-widget .interactive-canvas {
  cursor: default;
}

.inverse-widget .widget-body {
  grid-template-columns: 400px minmax(0, 1fr);
  align-items: flex-start;
  margin-bottom: 1.25rem;
}

.inverse-widget .controls-panel {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  align-content: start;
  gap: 0.9rem;
}

.inverse-widget .controls-panel > .matrix-input-grid,
.inverse-widget .controls-panel > .control-group,
.inverse-widget .controls-panel > .inverse-status,
.inverse-widget .controls-panel > .rule-callout {
  grid-column: 1 / -1;
}

.inverse-widget .chart-panel {
  align-self: flex-start;
  align-items: flex-start;
  justify-content: flex-start;
}

.inverse-widget .inverse-canvas-wrapper {
  width: 100%;
  max-width: 720px;
}

.inverse-widget .interactive-canvas {
  cursor: default;
}

.inverse-preset-grid {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.inverse-status {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
  padding: 0.75rem 0.9rem;
  border: 1px solid rgba(16, 185, 129, 0.3);
  border-radius: var(--radius-sm);
  background: rgba(16, 185, 129, 0.1);
  color: var(--text-main);
  font-size: 0.85rem;
}

.inverse-status output,
.inverse-result-card output,
.inverse-verification {
  color: var(--accent-emerald);
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
  font-size: 0.84rem;
  overflow-wrap: anywhere;
}

.inverse-derivation {
  display: flex;
  flex-direction: column;
  gap: 0.7rem;
  padding: 0.9rem;
  margin-top: 0.25rem;
  border: 1px solid rgba(6, 182, 212, 0.3);
  border-radius: var(--radius-sm);
  background: rgba(6, 182, 212, 0.05);
}

.inverse-derivation h4 {
  color: var(--accent-cyan);
  font-size: 0.95rem;
}

.inverse-formula,
.inverse-verification,
.inverse-recovery-state {
  margin: 0;
  line-height: 1.5;
}

.inverse-formula,
.inverse-recovery-state {
  color: var(--text-muted);
  font-size: 0.82rem;
}

.inverse-result-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.65rem;
}

.inverse-result-card {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
  min-width: 0;
  padding: 0.65rem;
  border: 1px solid var(--border-color);
  border-radius: 0.35rem;
  background: var(--bg-primary);
}

.inverse-result-card strong {
  color: var(--text-muted);
  font-size: 0.75rem;
}

.inverse-result-card.result {
  border-color: rgba(16, 185, 129, 0.4);
}

@media (max-width: 1100px) {
  .composition-widget .widget-body,
  .inverse-widget .widget-body {
    grid-template-columns: 1fr;
  }

  .composition-widget .chart-panel,
  .inverse-widget .chart-panel {
    justify-content: center;
  }
}

@media (max-width: 900px) {

  .composition-entry-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 600px) {
  .composition-widget .controls-panel,
  .inverse-widget .controls-panel {
    display: flex;
  }

  .inverse-result-grid {
    grid-template-columns: 1fr;
  }

  .composition-matrix-flow {
    grid-template-columns: 1fr;
  }

  .composition-matrix-operator {
    text-align: center;
    transform: rotate(90deg);
  }
}

body.light-mode .matrix-box {
  background: rgba(6, 182, 212, 0.06);
}

/* LaTeX Style Mathematical Brackets */
.matrix-box::before, .matrix-box::after {
  content: '';
  position: absolute;
  top: 4px;
  bottom: 4px;
  width: 8px;
  border: 3px solid var(--accent-cyan);
  pointer-events: none;
}

.matrix-box::before {
  left: 0;
  border-right: none;
  border-radius: 8px 0 0 8px;
}

.matrix-box::after {
  right: 0;
  border-left: none;
  border-radius: 0 8px 8px 0;
}

/* Fix CSS Grid Input Overflow & Browser Defaults */
.matrix-box input {
  min-width: 0;
  width: 100%;
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  color: var(--text-main);
  font-family: var(--font-mono);
  font-size: 1rem;
  font-weight: 600;
  padding: 0.5rem 0.2rem;
  text-align: center;
  border-radius: 6px;
  box-sizing: border-box;
  -moz-appearance: textfield;
  transition: all 0.2s ease;
}

body.light-mode .matrix-box input {
  background: #ffffff;
  border-color: #cbd5e1;
  color: #0f172a;
}

.matrix-box input::-webkit-outer-spin-button,
.matrix-box input::-webkit-inner-spin-button {
  -webkit-appearance: none;
  margin: 0;
}

.matrix-box input:focus {
  border-color: var(--accent-cyan);
  box-shadow: 0 0 10px rgba(6, 182, 212, 0.35);
  outline: none;
}

.matrix-box input.symmetric-linked {
  opacity: 0.7;
  border-style: dashed;
  background: rgba(6, 182, 212, 0.08);
}

.matrix-box.system-inputs {
  grid-template-columns: 1fr 1fr 1fr;
}

.system-equations {
  display: grid;
  gap: 0.3rem;
  font-family: var(--font-mono);
  color: var(--text-muted);
  font-size: 0.82rem;
}

.system-rref-panel {
  display: grid;
  gap: 0.45rem;
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: 0.8rem;
  font-size: 0.82rem;
}

.system-rref-panel p { margin: 0; color: var(--text-muted); }

.system-matrix-display { display: flex; justify-content: center; min-height: 62px; }

.system-matrix {
  border-collapse: separate;
  border-spacing: 0.35rem 0.18rem;
  font-family: var(--font-mono);
  color: var(--text-main);
}

.system-matrix td { min-width: 42px; text-align: center; }
.system-matrix .augmented-column { border-left: 2px solid var(--accent-cyan); padding-left: 0.55rem; }
.system-presets { grid-template-columns: repeat(3, 1fr); }

body.light-mode .system-rref-panel { background: #f8fafc; border-color: #e2e8f0; }

.btn-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.4rem;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.4rem;
  padding: 0.55rem 0.9rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  font-size: 0.8rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s ease;
}

.btn-preset {
  background: var(--bg-secondary);
  color: var(--text-muted);
}

.btn-preset:hover {
  background: rgba(6, 182, 212, 0.15);
  color: var(--accent-cyan);
  border-color: var(--accent-cyan);
}

.btn-preset.active {
  background: rgba(6, 182, 212, 0.25);
  color: var(--accent-cyan);
  border-color: var(--accent-cyan);
}

.btn-primary {
  background: linear-gradient(135deg, var(--accent-cyan), var(--accent-blue));
  color: #fff;
  border: none;
  box-shadow: 0 4px 12px rgba(6, 182, 212, 0.3);
}

.btn-primary:hover {
  filter: brightness(1.1);
  transform: translateY(-1px);
}

.btn-secondary {
  background: var(--bg-secondary);
  color: var(--text-main);
}

.btn-secondary:hover {
  border-color: var(--accent-cyan);
}

.stats-summary-box {
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
  background: var(--bg-secondary);
  padding: 0.8rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  font-size: 0.82rem;
}

body.light-mode .stats-summary-box {
  background: #f8fafc;
  border-color: #e2e8f0;
}

.stat-indicator {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  justify-content: space-between;
}

.ind-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  display: inline-block;
}

.rule-callout {
  display: flex;
  align-items: flex-start;
  gap: 0.5rem;
  background: rgba(6, 182, 212, 0.1);
  border-left: 3px solid var(--accent-cyan);
  padding: 0.6rem 0.8rem;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  font-size: 0.8rem;
  color: var(--text-main);
}

.chart-panel {
  display: flex;
  align-items: center;
  justify-content: center;
}

.canvas-wrapper {
  position: relative;
  width: 100%;
  max-width: 580px;
  background: #090d16;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  overflow: hidden;
  box-shadow: inset 0 0 20px rgba(0,0,0,0.5);
}

body.light-mode .canvas-wrapper {
  background: #ffffff;
  border-color: #cbd5e1;
  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.05);
}

canvas {
  display: block;
  width: 100%;
  height: auto;
}

canvas.interactive-canvas {
  cursor: grab;
}

canvas.interactive-canvas:active {
  cursor: grabbing;
}

.canvas-hint {
  position: absolute;
  bottom: 8px;
  right: 12px;
  font-size: 0.72rem;
  color: var(--text-dim);
  background: rgba(15, 23, 42, 0.75);
  padding: 2px 8px;
  border-radius: 4px;
  pointer-events: none;
}

body.light-mode .canvas-hint {
  background: rgba(255, 255, 255, 0.85);
  color: #475569;
}

/* 8. Subtabs & Quiz / Cheatsheet */
.sub-tab-bar {
  display: flex;
  gap: 0.6rem;
  margin-bottom: 1.5rem;
  border-bottom: 1px solid var(--border-color);
  padding-bottom: 0.5rem;
}

.sub-tab-btn {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.6rem 1rem;
  background: transparent;
  border: none;
  color: var(--text-muted);
  font-size: 0.88rem;
  font-weight: 500;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all 0.2s ease;
}

.sub-tab-btn:hover {
  color: var(--text-main);
  background: var(--bg-secondary);
}

.sub-tab-btn.active {
  background: var(--bg-secondary);
  color: var(--accent-cyan);
  font-weight: 600;
  border-bottom: 2px solid var(--accent-cyan);
}

.subtab-content {
  display: none;
}

.subtab-content.active {
  display: block;
}

/* Quiz Styles */
.quiz-container {
  max-width: 780px;
  margin: 0 auto;
}

.quiz-progress-bar {
  height: 6px;
  background: var(--bg-secondary);
  border-radius: 3px;
  overflow: hidden;
  margin-bottom: 1.5rem;
}

.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--accent-cyan), var(--accent-emerald));
  transition: width 0.3s ease;
}

.quiz-card {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 2rem;
  box-shadow: var(--shadow-subtle);
}

.quiz-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1.2rem;
}

.question-number {
  font-size: 0.85rem;
  color: var(--accent-cyan);
  font-weight: 600;
  margin-right: 0.6rem;
}

.quiz-cat-badge {
  font-size: 0.75rem;
  padding: 0.15rem 0.5rem;
  border-radius: 4px;
  background: rgba(139, 92, 246, 0.15);
  color: var(--accent-purple);
  font-weight: 500;
}

.quiz-score-badge {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  background: rgba(16, 185, 129, 0.15);
  color: var(--accent-emerald);
  padding: 0.2rem 0.6rem;
  border-radius: 4px;
}

.question-text {
  font-size: 1.15rem;
  margin-bottom: 1.5rem;
  line-height: 1.45;
}

.options-grid {
  display: flex;
  flex-direction: column;
  gap: 0.8rem;
  margin-bottom: 1.5rem;
}

.option-btn {
  display: flex;
  align-items: flex-start;
  gap: 0.75rem;
  padding: 0.9rem 1.2rem;
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  color: var(--text-main);
  font-size: 0.92rem;
  text-align: left;
  cursor: pointer;
  transition: all 0.2s ease;
}

.option-btn:hover {
  border-color: var(--accent-cyan);
  background: rgba(6, 182, 212, 0.05);
}

.option-btn.selected {
  border-color: var(--accent-cyan);
  background: rgba(6, 182, 212, 0.12);
}

.option-btn.correct {
  border-color: var(--accent-emerald);
  background: rgba(16, 185, 129, 0.18);
  color: #fff;
}

.option-btn.incorrect {
  border-color: var(--accent-rose);
  background: rgba(244, 63, 94, 0.18);
}

.explanation-box {
  background: rgba(6, 182, 212, 0.08);
  border-left: 4px solid var(--accent-cyan);
  padding: 1rem 1.2rem;
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  margin-bottom: 1.5rem;
  font-size: 0.9rem;
}

.explanation-box.hidden, .quiz-results-card.hidden, .quiz-card.hidden {
  display: none !important;
}

.exp-header {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  color: var(--accent-cyan);
  margin-bottom: 0.4rem;
}

.quiz-footer {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
}

.quiz-results-card {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 2.5rem 2rem;
  text-align: center;
}

.result-icon {
  width: 64px;
  height: 64px;
  color: var(--accent-amber);
  margin-bottom: 1rem;
}

.final-score-text {
  font-size: 1.1rem;
  margin-bottom: 1.5rem;
}

.final-score-text strong {
  font-size: 1.6rem;
  color: var(--accent-cyan);
}

.score-breakdown-box {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 1rem;
  margin: 1.5rem 0 2rem 0;
  text-align: left;
}

.breakdown-card {
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: 0.8rem 1rem;
}

.breakdown-title {
  font-size: 0.8rem;
  color: var(--text-muted);
}

.breakdown-score {
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--accent-emerald);
}

/* Cheatsheet Styles */
.cheatsheet-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(340px, 1fr));
  gap: 1.5rem;
}

.cheat-card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  backdrop-filter: blur(10px);
}

.cheat-card h3 {
  font-size: 1.1rem;
  color: var(--accent-cyan);
  margin-bottom: 1rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  border-bottom: 1px solid var(--border-color);
  padding-bottom: 0.5rem;
}

.cheat-item {
  margin-bottom: 1rem;
  font-size: 0.9rem;
}

.cheat-item p {
  color: var(--text-muted);
  margin: 0.3rem 0;
}

.cheat-item ul {
  padding-left: 1.2rem;
  color: var(--text-muted);
}

/* 9. Footer */
.footer {
  border-top: 1px solid var(--border-color);
  padding: 2rem 1.5rem;
  margin-top: 4rem;
  text-align: center;
  color: var(--text-dim);
  font-size: 0.85rem;
}

/* 10. Responsive Breakpoints */
@media (max-width: 768px) {
  .nav-container {
    flex-wrap: nowrap;
    gap: 0.35rem;
  }

  .brand-text { display: none; }
  .nav-track { grid-template-columns: 28px minmax(0, 1fr) 28px; gap: 0.2rem; }
  .nav-menu { grid-auto-columns: calc((100% - 0.5rem) / 2); gap: 0.5rem; }
  .nav-link { min-height: 48px; padding: 0.35rem; font-size: 0.75rem; gap: 0.3rem; }
  .nav-link span { font-size: 0.75rem; }
  .nav-scroll-btn { width: 28px; height: 34px; }
  .nav-controls { gap: 0.25rem; }
  .nav-controls span { display: none; }
  .theme-btn, .phonetic-btn, .lang-btn { width: 34px; height: 34px; padding: 0; justify-content: center; }

  .hero-banner {
    padding: 2rem 1rem;
  }

  .hero-text-block h1 {
    font-size: 1.6rem;
  }

  .hero-stats {
    width: 100%;
    justify-content: space-between;
  }

  .cards-grid {
    grid-template-columns: 1fr;
  }

  .interactive-widget {
    padding: 1rem;
  }
}

@media (max-width: 480px) {
  .navbar { padding: 0.45rem 0.5rem; }
  .brand-icon { width: 36px; height: 36px; }
  .nav-link span { display: none; }
  .nav-menu { grid-auto-columns: calc((100% - 0.5rem) / 2); }
  .matrix-box.system-inputs { grid-template-columns: 1fr 1fr 1fr; padding: 0.65rem; gap: 0.35rem; }
  .system-presets { grid-template-columns: 1fr; }
  .composition-order-toggle,
  .composition-preset-grid,
  .composition-entry-grid { grid-template-columns: 1fr; }

}

@media (min-width: 1500px) {
  .brand-subtitle { display: block; }
}

/* ==========================================================================
   Floating Watermark Badge (Option 3)
   ========================================================================== */
.floating-watermark-badge {
  position: fixed;
  bottom: 24px;
  right: 24px;
  z-index: 999;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 8px 16px;
  background: rgba(15, 23, 42, 0.8);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border: 1px solid rgba(255, 255, 255, 0.15);
  border-radius: 30px;
  color: #f8fafc;
  font-family: var(--font-mono);
  font-size: 0.825rem;
  font-weight: 600;
  letter-spacing: 0.5px;
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.3), 0 0 15px rgba(6, 182, 212, 0.2);
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  user-select: none;
  cursor: default;
}

body.light-mode .floating-watermark-badge {
  background: rgba(255, 255, 255, 0.88);
  border-color: rgba(0, 0, 0, 0.12);
  color: #0f172a;
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.08), 0 0 15px rgba(6, 182, 212, 0.15);
}

.floating-watermark-badge:hover {
  transform: translateY(-3px) scale(1.03);
  border-color: var(--accent-cyan);
  box-shadow: 0 12px 30px rgba(6, 182, 212, 0.35);
}

.badge-pulse {
  width: 8px;
  height: 8px;
  background-color: var(--accent-cyan);
  border-radius: 50%;
  box-shadow: 0 0 8px var(--accent-cyan);
  animation: badgePulse 2s infinite ease-in-out;
}

@keyframes badgePulse {
  0%, 100% { transform: scale(1); opacity: 0.8; }
  50% { transform: scale(1.35); opacity: 1; box-shadow: 0 0 12px var(--accent-cyan); }
}

.feedback-widget {
  position: fixed;
  right: 24px;
  bottom: 24px;
  z-index: 999;
}

.feedback-widget .floating-watermark-badge {
  position: relative;
  right: auto;
  bottom: auto;
  z-index: auto;
  appearance: none;
  cursor: pointer;
  font: inherit;
}

.feedback-widget .floating-watermark-badge:focus-visible,
.feedback-close:focus-visible,
.feedback-contact-link:focus-visible {
  outline: 3px solid rgba(6, 182, 212, 0.35);
  outline-offset: 3px;
}

.feedback-panel {
  position: absolute;
  right: 0;
  bottom: calc(100% + 12px);
  width: min(300px, calc(100vw - 32px));
  padding: 16px;
  border: 1px solid var(--border-accent);
  border-radius: var(--radius-md);
  background: var(--bg-glass);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  box-shadow: var(--shadow-subtle), var(--shadow-glow);
  animation: feedbackPanelEnter 180ms ease-out;
}

.feedback-panel[hidden] { display: none; }

.feedback-panel h2 {
  margin: 0 28px 10px 0;
  color: var(--text-main);
  font-size: 1rem;
}

.feedback-close {
  position: absolute;
  top: 10px;
  right: 10px;
  display: inline-grid;
  width: 30px;
  height: 30px;
  place-items: center;
  border: 0;
  border-radius: 50%;
  background: transparent;
  color: var(--text-muted);
  cursor: pointer;
}

.feedback-close:hover { background: var(--bg-card-hover); color: var(--text-main); }
.feedback-close svg { width: 16px; height: 16px; }

.feedback-contact-link {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  margin: 0 -8px;
  padding: 10px 8px;
  border-radius: var(--radius-sm);
  color: var(--text-muted);
  font-size: 0.75rem;
  text-decoration: none;
  transition: background-color 160ms ease, color 160ms ease;
}

.feedback-contact-link + .feedback-contact-link { border-top: 1px solid var(--border-color); }
.feedback-contact-link:hover { background: rgba(6, 182, 212, 0.08); }
.feedback-contact-link:hover strong { color: var(--accent-cyan); }
.feedback-contact-link > i,
.feedback-contact-link > svg {
  flex: 0 0 18px;
  width: 18px;
  height: 18px;
  margin-top: 2px;
  color: var(--accent-cyan);
}

.feedback-contact-content {
  display: flex;
  flex: 1 1 auto;
  flex-direction: column;
  min-width: 0;
  gap: 2px;
}

.feedback-contact-content > span { color: var(--text-muted); }
.feedback-contact-link strong {
  min-width: 0;
  overflow-wrap: anywhere;
  color: var(--text-main);
  font-size: 0.8rem;
  font-weight: 600;
  line-height: 1.35;
}

@keyframes feedbackPanelEnter {
  from { opacity: 0; transform: translateY(8px) scale(0.98); }
  to { opacity: 1; transform: translateY(0) scale(1); }
}

@media (max-width: 480px) {
  .feedback-widget { right: 12px; bottom: 16px; }
  .feedback-panel { width: min(300px, calc(100vw - 24px)); }
}

@media (prefers-reduced-motion: reduce) {
  .feedback-panel { animation: none; transition: none; }
}

input[aria-invalid="true"] {
  border-color: #f43f5e !important;
  box-shadow: 0 0 0 2px rgba(244, 63, 94, 0.18);
}