:root {
  /* Core Spacing & Radius */
  --border-radius-lg: 24px;
  --border-radius-md: 12px;
  --transition-fast: 0.1s ease;
  --transition-normal: 0.4s cubic-bezier(0.2, 0.8, 0.2, 1);
  --transition-bounce: 0.5s cubic-bezier(0.175, 0.885, 0.32, 1.275);

  /* DARK MODE: Midnight Violet & Neon Cyan (Cyber-Premium) */
  --bg-main: #0b0f19;        /* Deep abyss blue */
  --bg-base: #05080f;        /* Absolute shadow */
  --bg-header: rgba(11, 15, 25, 0.85);
  --bg-card: #151b2b;        /* Midnight panels */
  --bg-card-hover: #1e263c;
  --text-main: #f8fafc;      /* Crisp starlight white */
  --text-muted: #94a3b8;     /* Stealthy blue-grey */
  
  /* Bold Next-Gen Accents */
  --accent-primary: #8b5cf6; /* Vibrant Violet */
  --accent-secondary: #06b6d4; /* Electric Cyan */
  --accent-color: var(--accent-primary);
  
  /* Accessible Interaction Variables */
  --link-color: var(--accent-secondary);
  --link-hover-color: #ffffff;
  --link-hover-bg: #06b6d4;
  --vowel-vibrant: #f43f5e;   /* Neon Rose */
  --cons-vibrant: #10b981;    /* Matrix Emerald */
  
  --vowel-glow: rgba(244, 63, 94, 0.35);
  --cons-glow: rgba(16, 185, 129, 0.35);
  --accent-glow: rgba(139, 92, 246, 0.4);
  
  --card-border: #1e293b;
  --bg-sub-item: rgba(148, 163, 184, 0.05);
  
  /* Gradients (Punchy & Energetic) */
  --grad-vowel: linear-gradient(135deg, #f43f5e, #be123c);
  --grad-cons: linear-gradient(135deg, #10b981, #047857);
  --grad-premium: linear-gradient(135deg, #8b5cf6, #db2777);
}

[data-theme="light"] {
  /* LIGHT MODE: Frosty Coral & Mint (Clean EdTech) */
  --bg-main: #f8fafc;    /* Frosty cool white */
  --bg-base: #f1f5f9;    /* Crisp shadow panel */
  --bg-header: rgba(255, 255, 255, 0.9); 
  --bg-card: #ffffff;   
  --bg-card-hover: #f1f5f9;
  --text-main: #0f172a;  /* Heavy slate */
  --text-muted: #64748b;
  
  --accent-primary: #f43f5e; /* Vibrant Coral */
  --accent-secondary: #14b8a6; /* Fresh Mint */
  --accent-color: var(--accent-primary);
  
  /* Accessible Interaction Variables */
  --link-color: var(--accent-primary);
  --link-hover-color: #ffffff;
  --link-hover-bg: var(--accent-primary);
  --vowel-vibrant: #8b5cf6; /* Royal Violet */
  --cons-vibrant: #f59e0b;  /* Sunset Amber */
  
  --vowel-glow: rgba(139, 92, 246, 0.25);
  --cons-glow: rgba(245, 158, 11, 0.25);
  --accent-glow: rgba(244, 63, 94, 0.3);
  
  --card-border: rgba(15, 23, 42, 0.08); 
  --bg-sub-item: #f8fafc;
  
  --grad-vowel: linear-gradient(135deg, #a78bfa, #7c3aed);
  --grad-cons: linear-gradient(135deg, #fbbf24, #d97706);
  --grad-premium: linear-gradient(135deg, #f43f5e, #f97316);
}

/* Light Theme Specific Element Polish (Ultra Premium) */
[data-theme="light"] body {
  background-color: var(--bg-main);
  background-image: radial-gradient(circle at 10% 20%, rgba(79, 70, 229, 0.05), transparent 25%), 
                    radial-gradient(circle at 90% 80%, rgba(6, 182, 212, 0.05), transparent 25%);
  background-attachment: fixed;
}

[data-theme="light"] .app-header {
  box-shadow: 0 4px 30px rgba(0, 0, 0, 0.03);
  backdrop-filter: blur(24px);
  -webkit-backdrop-filter: blur(24px);
  border-bottom: 1px solid rgba(255, 255, 255, 0.6);
}

[data-theme="light"] .logo {
  background: linear-gradient(135deg, #0f172a, #334155);
  -webkit-background-clip: text;
  background-clip: text;
}

[data-theme="light"] .sound-card,
[data-theme="light"] .alphabet-card,
[data-theme="light"] .modal-content {
  box-shadow: 0 8px 24px -4px rgba(0, 0, 0, 0.04), 0 4px 10px -6px rgba(0, 0, 0, 0.02);
  border: 1px solid rgba(255, 255, 255, 0.9); /* Gives the 'glass cut' feeling */
}

[data-theme="light"] .sound-card:hover,
[data-theme="light"] .alphabet-card:hover {
  box-shadow: 0 25px 40px -10px rgba(79, 70, 229, 0.12), 0 0 20px var(--accent-glow);
  border-color: rgba(79, 70, 229, 0.25);
  background: #ffffff;
}

[data-theme="light"] .sound-symbol {
  background: linear-gradient(135deg, #1e293b, #475569) !important;
  -webkit-background-clip: text !important;
  background-clip: text !important;
  -webkit-text-fill-color: transparent !important;
}

[data-theme="light"] .sound-card:hover .sound-symbol {
  background: linear-gradient(135deg, #0f172a, #1e293b) !important;
  -webkit-background-clip: text !important;
  background-clip: text !important;
}

[data-theme="light"] .logo span {
  text-shadow: none;
}

[data-theme="light"] .symbol-toggle {
  background: rgba(0, 0, 0, 0.06);
  box-shadow: inset 0 2px 5px rgba(0,0,0,0.06), 0 1px 0 rgba(255,255,255,0.7);
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: 'Inter', system-ui, -apple-system, sans-serif;
}

body {
  background: var(--bg-main);
  color: var(--text-main);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  transition: background-color var(--transition-normal), color var(--transition-normal);
}

/* Base Accessible Links & General Focus (WCAG Compliant) */
a, .interactive-link {
  color: var(--link-color);
  text-decoration: underline;
  text-underline-offset: 3px;
  border-radius: 4px;
  padding: 0 2px;
  transition: color var(--transition-fast), background-color var(--transition-fast), text-decoration-color var(--transition-fast);
}

a:hover, .interactive-link:hover {
  background-color: var(--link-hover-bg);
  color: var(--link-hover-color);
  text-decoration-color: transparent;
}

/* Fix global background hover inside structural elements */
.header-content a, .header-content a:hover {
  background-color: transparent !important;
  text-decoration: none;
}

button:focus-visible, a:focus-visible {
  outline: 3px solid var(--accent-color);
  outline-offset: 3px;
}

/* Custom Scrollbar for Premium Feel */
::-webkit-scrollbar {
  width: 10px;
}
::-webkit-scrollbar-track {
  background: var(--bg-main);
}
::-webkit-scrollbar-thumb {
  background: var(--bg-card-hover);
  border-radius: 10px;
  border: 2px solid var(--bg-main);
}
::-webkit-scrollbar-thumb:hover {
  background: var(--accent-color);
}

.ipa-secondary {
  font-size: 0.7rem;
  color: var(--text-muted);
  font-weight: 500;
  margin-top: -0.25rem;
  margin-bottom: 0.25rem;
}

/* Header & Nav */
.app-header {
  background-color: var(--bg-header);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--card-border);
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: 0 10px 30px -10px rgba(0, 0, 0, 0.4);
}

.header-content {
  max-width: 1200px;
  margin: 0 auto;
  padding: 1.5rem 2rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 1rem;
}

.logo {
  font-size: 2rem;
  font-weight: 900;
  letter-spacing: -1px;
  background: linear-gradient(135deg, #fff, #94a3b8);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}
.logo span {
  background: var(--grad-vowel);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  filter: drop-shadow(0 0 10px var(--vowel-glow));
}

/* Symbol Toggle */
.symbol-toggle {
  display: flex;
  background: rgba(0, 0, 0, 0.15); /* Adjusted for light/dark */
  border-radius: 24px;
  padding: 0.25rem;
  box-shadow: inset 0 2px 4px rgba(0,0,0,0.2), 0 1px 3px rgba(255,255,255,0.05);
}

.toggle-btn {
  background: transparent;
  border: none;
  color: var(--text-muted);
  padding: 0.6rem 1.2rem;
  border-radius: 20px;
  font-weight: 600;
  font-size: 0.85rem;
  cursor: pointer;
  transition: all var(--transition-normal);
}

.toggle-btn:hover {
  color: var(--text-main);
  background: var(--bg-card-hover);
}

.toggle-btn.active {
  background: var(--grad-premium);
  color: #fff;
  box-shadow: 0 10px 20px -5px var(--accent-glow);
}

/* Tabs */
.tabs {
  display: flex;
  justify-content: center;
  justify-content: safe center;
  gap: 1.5rem;
  padding: 0 1rem;
  background: rgba(0, 0, 0, 0.1);
  overflow-x: auto;
  white-space: nowrap;
  -webkit-overflow-scrolling: touch;
  scrollbar-width: none;
}
.tabs::-webkit-scrollbar {
  display: none;
}

.tab-btn {
  background: none;
  border: none;
  color: var(--text-muted);
  font-size: 1rem;
  font-weight: 600;
  padding: 1rem 0;
  cursor: pointer;
  border-bottom: 3px solid transparent;
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  position: relative;
  text-transform: uppercase;
  letter-spacing: 1.5px;
}

.tab-btn::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 50%;
  width: 0;
  height: 4px;
  background: var(--grad-premium);
  border-radius: 4px 4px 0 0;
  transition: all var(--transition-bounce);
  transform: translateX(-50%);
}

.tab-btn:hover::after {
  width: 100%;
}

.tab-btn:hover {
  color: var(--text-main);
}

.tab-btn.active {
  color: var(--text-main);
}
.tab-btn.active::after {
  width: 100%;
}
.tab-btn[data-tab="vowels"].active {
  color: var(--vowel-vibrant);
}
.tab-btn[data-tab="vowels"].active::after {
  background: var(--grad-vowel);
}
.tab-btn[data-tab="consonants"].active {
  color: var(--cons-vibrant);
}
.tab-btn[data-tab="consonants"].active::after {
  background: var(--grad-cons);
}

/* Sub-Tabs */
.sub-tabs {
  display: flex;
  justify-content: center;
  justify-content: safe center;
  gap: 1rem;
  padding: 0.5rem 1rem;
  background: var(--bg-header);
  border-bottom: 1px solid rgba(255, 255, 255, 0.05);
  flex-wrap: nowrap;
  overflow-x: auto;
  white-space: nowrap;
  -webkit-overflow-scrolling: touch;
  transition: max-height 0.3s ease, opacity 0.3s ease, padding 0.3s ease;
  scrollbar-width: none;
}
.sub-tabs::-webkit-scrollbar {
  display: none;
}

.sub-tabs.hidden {
  max-height: 0;
  opacity: 0;
  padding-top: 0;
  padding-bottom: 0;
  border-bottom: none;
}

.sub-tab-btn {
  background: rgba(0,0,0,0.05);
  border: 1px solid var(--card-border);
  color: var(--text-muted);
  font-size: 0.85rem;
  padding: 0.4rem 1rem;
  border-radius: 20px;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.sub-tab-btn:hover {
  background: rgba(0,0,0,0.1);
  color: var(--text-main);
}

.sub-tab-btn.active {
  background: var(--grad-premium); 
  border-color: transparent;
  color: #fff;
  box-shadow: 0 8px 16px -4px var(--accent-glow);
}

/* Main Content */
.app-main {
  flex: 1;
  max-width: 1200px;
  margin: 0 auto;
  padding: 3rem 2rem;
  width: 100%;
}

.cards-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 2rem;
}

/* Card Styling (Premium Polish) */
.sound-card {
  background: var(--bg-card);
  border-radius: var(--border-radius-lg);
  padding: 1.8rem;
  border: 1px solid var(--card-border);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  transition: all var(--transition-bounce);
  cursor: pointer;
  position: relative;
  display: flex;
  flex-direction: column;
  overflow: hidden;
  box-shadow: 0 15px 35px -5px rgba(0, 0, 0, 0.4);
}

.sound-card:active {
  transform: scale(0.95);
}

.sound-card::after {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 4px;
  background: linear-gradient(90deg, transparent, var(--accent-color), transparent);
  opacity: 0;
  transition: opacity 0.3s;
}

.sound-card:hover {
  transform: translateY(-12px) scale(1.02);
  background: var(--bg-card-hover);
  border-color: var(--accent-primary);
  box-shadow: 0 25px 45px -10px rgba(0, 0, 0, 0.6), 0 0 20px var(--accent-glow);
}

/* Glass shine effect */
.sound-card::before {
  content: '';
  position: absolute;
  top: -50%;
  left: -50%;
  width: 200%;
  height: 200%;
  background: linear-gradient(45deg, transparent, rgba(255,255,255,0.05), transparent);
  transform: rotate(30deg);
  pointer-events: none;
  transition: 0.6s;
}

.sound-card:hover::before {
  left: 100%;
  top: 100%;
}

.card-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1.25rem;
}

.sound-symbol {
  font-size: 3.8rem;
  font-weight: 900;
  line-height: 1;
  background: linear-gradient(135deg, #ffffff, #94a3b8);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  transition: transform 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

.sound-card:hover .sound-symbol {
  transform: scale(1.15) rotate(-2deg);
  background: #fff;
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}

.sound-category {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 2px;
  color: var(--text-muted);
  font-weight: 800;
  margin-bottom: 0.5rem;
}

.play-btn {
  background: var(--grad-premium);
  border: none;
  width: 52px;
  height: 52px;
  min-width: 52px;
  min-height: 52px;
  border-radius: 18px;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: all var(--transition-bounce);
  color: #fff;
  box-shadow: 0 8px 15px -5px var(--accent-glow);
}

.play-btn:hover {
  transform: scale(1.15) rotate(8deg);
  filter: brightness(1.2) saturate(1.2);
}

.play-btn svg {
  width: 24px;
  height: 24px;
  fill: currentColor;
}

.graphs-summary {
  font-size: 0.95rem;
  color: var(--text-muted);
  display: flex;
  align-items: center;
  gap: 0.6rem;
  font-weight: 500;
}

.expand-icon {
  font-size: 0.9rem;
  transition: transform 0.4s;
}

/* Visual Step-down (Graphemes list) */
.graphemes-list {
  margin-top: 1.5rem;
  display: grid;
  grid-template-columns: 1fr;
  gap: 0.8rem;
  max-height: 0;
  opacity: 0;
  overflow: hidden;
  transition: all 0.5s cubic-bezier(0.4, 0, 0.2, 1);
}

.sound-card.expanded .graphemes-list {
  max-height: 1000px;
  opacity: 1;
  padding-bottom: 1rem;
}

.grapheme-item {
  display: flex;
  justify-content: space-between;
  align-items: center;
  background: var(--bg-sub-item);
  padding: 0.8rem 1.2rem;
  border-radius: 12px;
  border: 1px solid var(--card-border);
  transition: transform 0.3s;
}

.grapheme-item:hover {
  transform: scale(1.02);
  background: rgba(255, 255, 255, 0.06);
}

.graph-rep {
  font-weight: 800;
  font-size: 1.2rem;
  color: var(--text-main);
}

.graph-type {
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--accent-color);
  text-transform: uppercase;
  letter-spacing: 1px;
}

.more-examples-btn {
  display: inline-flex;
  align-items: center;
  margin-top: 1rem;
  font-size: 0.8rem;
  font-weight: 800;
  letter-spacing: 1px;
  text-transform: uppercase;
  color: #fff;
  background: var(--grad-vowel);
  border: none;
  padding: 0.75rem 1.5rem;
  border-radius: 12px;
  cursor: pointer;
  transition: all var(--transition-bounce);
  box-shadow: 0 8px 15px -5px var(--vowel-glow);
}

.more-examples-btn:hover {
  transform: translateY(-3px) scale(1.05);
  box-shadow: 0 8px 20px var(--accent-glow);
  filter: brightness(1.1);
}

/* Theme Toggle UI */
.theme-toggle {
  background: var(--bg-card);
  border: 1px solid var(--card-border);
  color: var(--text-main);
  width: 44px;
  height: 44px;
  border-radius: 50%;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition-bounce);
  position: relative;
  overflow: hidden;
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.1);
  margin-left: auto;
  margin-right: 1.5rem;
}

.theme-toggle:hover {
  background: var(--bg-card-hover);
  border-color: var(--accent-primary);
  transform: scale(1.1);
  box-shadow: 0 6px 15px rgba(0, 0, 0, 0.2);
}

.theme-toggle svg {
  width: 20px;
  height: 20px;
  fill: currentColor;
  position: absolute;
  transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1), opacity 0.6s ease;
}

.theme-toggle .moon-icon {
  transform: translateY(0) rotate(0);
  opacity: 1;
}

.theme-toggle .sun-icon {
  transform: translateY(-150%) rotate(-45deg);
  opacity: 0;
}

[data-theme="light"] .theme-toggle .sun-icon {
  transform: translateY(0) rotate(0);
  opacity: 1;
}

[data-theme="light"] .theme-toggle .moon-icon {
  transform: translateY(150%) rotate(45deg);
  opacity: 0;
}

/* Modal Implementation */
.modal-overlay {
  position: fixed;
  top: 0;
  left: 0;
  width: 100vw;
  height: 100vh;
  background: rgba(15, 23, 42, 0.6);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  z-index: 2000;
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.4s ease, visibility 0.4s;
}

.modal-overlay.active {
  opacity: 1;
  visibility: visible;
}

.modal-content {
  background: var(--bg-card);
  backdrop-filter: blur(24px);
  -webkit-backdrop-filter: blur(24px);
  border: 1px solid var(--card-border);
  border-radius: 24px;
  padding: 2.5rem;
  width: 90%;
  max-width: 500px;
  max-height: 85vh;
  overflow-y: auto;
  position: relative;
  box-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.5);
  transform: scale(0.8);
  transition: transform 0.5s cubic-bezier(0.34, 1.56, 0.64, 1), opacity 0.4s;
  opacity: 0;
}

.modal-overlay.active .modal-content {
  transform: scale(1);
  opacity: 1;
}

.modal-close {
  position: absolute;
  top: 1rem;
  right: 1.5rem;
  background: none;
  border: none;
  color: var(--text-muted);
  font-size: 2rem;
  line-height: 1;
  cursor: pointer;
  transition: color var(--transition-fast);
}

.modal-close:hover {
  color: #fff;
}

#modal-title {
  margin-bottom: 1.5rem;
  font-size: 1.5rem;
  color: var(--text-main);
  padding-right: 2rem;
}

.word-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 1rem;
}

.word-grid-item {
  background: var(--bg-sub-item);
  padding: 0.8rem 1rem;
  border-radius: 18px;
  text-align: center;
  font-size: 1.1rem;
  font-weight: 600;
  border: 1px solid rgba(255, 255, 255, 0.1);
  transition: all 0.2s;
  cursor: pointer;
  color: var(--text-main);
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
  min-height: 48px;
  justify-content: center;
}

.word-grid-item:hover {
  background: var(--accent-color);
  color: #0f172a;
  transform: translateY(-3px);
  box-shadow: 0 8px 20px var(--accent-glow);
  border-color: transparent;
}

/* Toast Notification */
.toast-container {
  position: fixed;
  bottom: 2rem;
  right: 2rem;
  z-index: 1000;
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.toast {
  background: var(--bg-card);
  color: var(--text-main);
  padding: 1rem 1.8rem;
  border-radius: var(--border-radius-md);
  box-shadow: 0 15px 30px rgba(0,0,0,0.4);
  border: 1px solid var(--card-border);
  border-left: 6px solid var(--accent-color);
  display: flex;
  align-items: center;
  gap: 1rem;
  transform: translateX(120%);
  transition: transform 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

.toast.show {
  transform: translateX(0);
}

/* Responsive */
@media (max-width: 768px) {
  .header-content {
    flex-direction: column;
    align-items: center;
    text-align: center;
    padding: 1rem;
  }
  .theme-toggle {
    margin: 1rem auto 0 auto;
  }
  .app-main {
    padding: 1.5rem 1rem;
  }
  .cards-grid {
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 1.5rem;
  }
  .modal-content {
    padding: 1.5rem;
    width: 95%;
  }
}

@media (max-width: 480px) {
  .cards-grid {
    grid-template-columns: 1fr;
  }
  .sound-card {
    padding: 1.2rem;
  }
  .sound-symbol {
    font-size: 3rem;
  }
  .word-grid {
    grid-template-columns: 1fr;
  }
}

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

/* Footer */
.app-footer {
  text-align: center;
  padding: 2rem;
  margin-top: auto;
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--text-muted);
  border-top: 1px solid var(--card-border);
  background: rgba(0, 0, 0, 0.05);
}

.app-footer p {
  opacity: 0.8;
  letter-spacing: 0.5px;
}