/* ============================================
   ChildMath — CSS Design System
   A vibrant, kid-friendly math learning website
   ============================================ */

/* ---------- Google Fonts ---------- */
@import url('https://fonts.googleapis.com/css2?family=Fredoka+One&family=Nunito:wght@400;600;700;800&display=swap');

/* ---------- CSS Custom Properties ---------- */
:root {
  /* Primary Palette */
  --color-primary: #6C5CE7;
  --color-primary-light: #A29BFE;
  --color-primary-dark: #4834D4;

  /* Accent Colors */
  --color-accent-pink: #FD79A8;
  --color-accent-orange: #FDCB6E;
  --color-accent-green: #00B894;
  --color-accent-blue: #74B9FF;
  --color-accent-red: #FF6B6B;
  --color-accent-teal: #00CEC9;

  /* Backgrounds */
  --bg-gradient-start: #667EEA;
  --bg-gradient-end: #764BA2;
  --bg-body: #F8F9FF;
  --bg-card: rgba(255, 255, 255, 0.85);
  --bg-card-hover: rgba(255, 255, 255, 0.95);

  /* Text */
  --text-primary: #2D3436;
  --text-secondary: #636E72;
  --text-light: #B2BEC3;
  --text-white: #FFFFFF;

  /* Shadows */
  --shadow-soft: 0 4px 20px rgba(108, 92, 231, 0.15);
  --shadow-medium: 0 8px 32px rgba(108, 92, 231, 0.2);
  --shadow-strong: 0 12px 48px rgba(108, 92, 231, 0.3);
  --shadow-glow: 0 0 30px rgba(108, 92, 231, 0.4);

  /* Border Radius */
  --radius-sm: 12px;
  --radius-md: 20px;
  --radius-lg: 28px;
  --radius-xl: 40px;
  --radius-round: 50%;

  /* Spacing */
  --space-xs: 6px;
  --space-sm: 12px;
  --space-md: 20px;
  --space-lg: 32px;
  --space-xl: 48px;
  --space-2xl: 64px;

  /* Typography */
  --font-display: 'Fredoka One', cursive;
  --font-body: 'Nunito', sans-serif;
  --font-size-xs: 0.75rem;
  --font-size-sm: 0.875rem;
  --font-size-md: 1rem;
  --font-size-lg: 1.25rem;
  --font-size-xl: 1.5rem;
  --font-size-2xl: 2rem;
  --font-size-3xl: 3rem;
  --font-size-4xl: 4rem;

  /* Transitions */
  --transition-fast: 0.2s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-smooth: 0.4s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-bounce: 0.5s cubic-bezier(0.68, -0.55, 0.265, 1.55);
}

/* ---------- Dark Mode ---------- */
[data-theme="dark"] {
  --bg-body: #1A1A2E;
  --bg-card: rgba(30, 30, 60, 0.85);
  --bg-card-hover: rgba(40, 40, 80, 0.95);
  --text-primary: #E4E4FF;
  --text-secondary: #A0A0CC;
  --text-light: #6060AA;
  --shadow-soft: 0 4px 20px rgba(0, 0, 0, 0.3);
  --shadow-medium: 0 8px 32px rgba(0, 0, 0, 0.4);
  --shadow-strong: 0 12px 48px rgba(0, 0, 0, 0.5);
}

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

html {
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-body);
  background: var(--bg-body);
  color: var(--text-primary);
  min-height: 100vh;
  overflow-x: hidden;
  transition: background var(--transition-smooth), color var(--transition-smooth);
}

/* ---------- Animated Background ---------- */
.bg-decoration {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: 0;
  pointer-events: none;
  overflow: hidden;
}

.bg-shape {
  position: absolute;
  border-radius: var(--radius-round);
  opacity: 0.08;
  animation: float 20s ease-in-out infinite;
}

.bg-shape:nth-child(1) {
  width: 400px;
  height: 400px;
  background: var(--color-primary);
  top: -100px;
  right: -100px;
  animation-delay: 0s;
}

.bg-shape:nth-child(2) {
  width: 300px;
  height: 300px;
  background: var(--color-accent-pink);
  bottom: -50px;
  left: -80px;
  animation-delay: -5s;
}

.bg-shape:nth-child(3) {
  width: 200px;
  height: 200px;
  background: var(--color-accent-orange);
  top: 40%;
  left: 60%;
  animation-delay: -10s;
}

.bg-shape:nth-child(4) {
  width: 250px;
  height: 250px;
  background: var(--color-accent-green);
  top: 60%;
  left: 10%;
  animation-delay: -15s;
}

/* ---------- Container ---------- */
.container {
  max-width: 900px;
  margin: 0 auto;
  padding: 0 var(--space-md);
  position: relative;
  z-index: 1;
}

/* ---------- Header / Navbar ---------- */
.navbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: var(--space-md) 0;
  margin-bottom: var(--space-lg);
}

.logo {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  text-decoration: none;
}

.logo-icon {
  width: 48px;
  height: 48px;
  border-radius: var(--radius-sm);
  object-fit: cover;
}

.logo-text {
  font-family: var(--font-display);
  font-size: var(--font-size-xl);
  background: linear-gradient(135deg, var(--color-primary), var(--color-accent-pink));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.theme-toggle {
  background: var(--bg-card);
  border: 2px solid transparent;
  border-radius: var(--radius-round);
  width: 48px;
  height: 48px;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  font-size: var(--font-size-lg);
  box-shadow: var(--shadow-soft);
  transition: all var(--transition-bounce);
  backdrop-filter: blur(12px);
}

.theme-toggle:hover {
  transform: rotate(30deg) scale(1.1);
  box-shadow: var(--shadow-medium);
}

/* ---------- Hero Section ---------- */
.hero {
  text-align: center;
  padding: var(--space-xl) 0;
  animation: fadeInUp 0.8s ease-out;
}

.hero-mascot {
  width: 150px;
  height: 150px;
  margin: 0 auto var(--space-lg);
  animation: bounce 2s ease-in-out infinite;
  filter: drop-shadow(0 10px 20px rgba(108, 92, 231, 0.3));
}

.hero-mascot img {
  width: 100%;
  height: 100%;
  object-fit: contain;
}

.hero h1 {
  font-family: var(--font-display);
  font-size: var(--font-size-4xl);
  margin-bottom: var(--space-sm);
  background: linear-gradient(135deg, var(--color-primary), var(--color-accent-pink), var(--color-accent-orange));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  background-size: 200% 200%;
  animation: gradientShift 4s ease-in-out infinite;
}

.hero p {
  font-size: var(--font-size-lg);
  color: var(--text-secondary);
  margin-bottom: var(--space-lg);
  font-weight: 600;
}

.btn-start {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  background: linear-gradient(135deg, var(--color-primary), var(--color-primary-dark));
  color: var(--text-white);
  font-family: var(--font-display);
  font-size: var(--font-size-xl);
  padding: var(--space-md) var(--space-xl);
  border: none;
  border-radius: var(--radius-xl);
  cursor: pointer;
  box-shadow: var(--shadow-medium);
  transition: all var(--transition-bounce);
  text-decoration: none;
}

.btn-start:hover {
  transform: translateY(-4px) scale(1.05);
  box-shadow: var(--shadow-strong), var(--shadow-glow);
}

.btn-start:active {
  transform: translateY(0) scale(0.98);
}

.btn-start .emoji {
  font-size: var(--font-size-2xl);
  animation: wiggle 1s ease-in-out infinite;
}

/* ---------- Game Section ---------- */
.game-section {
  display: none;
  animation: fadeInUp 0.6s ease-out;
}

.game-section.active {
  display: block;
}

/* ---------- Stats Bar ---------- */
.stats-bar {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: var(--space-sm);
  margin-bottom: var(--space-lg);
}

.stat-card {
  background: var(--bg-card);
  backdrop-filter: blur(16px);
  border-radius: var(--radius-md);
  padding: var(--space-md);
  text-align: center;
  box-shadow: var(--shadow-soft);
  transition: all var(--transition-smooth);
  border: 2px solid transparent;
}

.stat-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-medium);
}

.stat-card .stat-icon {
  font-size: var(--font-size-2xl);
  margin-bottom: var(--space-xs);
}

.stat-card .stat-value {
  font-family: var(--font-display);
  font-size: var(--font-size-2xl);
  color: var(--color-primary);
}

.stat-card .stat-label {
  font-size: var(--font-size-xs);
  color: var(--text-secondary);
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 1px;
}

.stat-card.highlight {
  border-color: var(--color-accent-orange);
  background: linear-gradient(135deg, rgba(253, 203, 110, 0.1), rgba(253, 203, 110, 0.05));
}

/* ---------- Controls Bar ---------- */
.controls-bar {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-sm);
  justify-content: center;
  margin-bottom: var(--space-lg);
}

.op-btn {
  background: var(--bg-card);
  backdrop-filter: blur(12px);
  border: 2px solid transparent;
  border-radius: var(--radius-lg);
  padding: var(--space-sm) var(--space-md);
  font-family: var(--font-body);
  font-weight: 700;
  font-size: var(--font-size-md);
  cursor: pointer;
  transition: all var(--transition-bounce);
  box-shadow: var(--shadow-soft);
  display: flex;
  align-items: center;
  gap: var(--space-xs);
  color: var(--text-primary);
}

.op-btn:hover {
  transform: translateY(-3px) scale(1.05);
  box-shadow: var(--shadow-medium);
}

.op-btn.active {
  border-color: var(--color-primary);
  background: linear-gradient(135deg, rgba(108, 92, 231, 0.15), rgba(108, 92, 231, 0.05));
  color: var(--color-primary);
}

.op-btn .op-icon {
  font-size: var(--font-size-lg);
}

/* Difficulty Buttons */
.diff-btn {
  background: var(--bg-card);
  backdrop-filter: blur(12px);
  border: 2px solid transparent;
  border-radius: var(--radius-lg);
  padding: var(--space-xs) var(--space-md);
  font-family: var(--font-body);
  font-weight: 700;
  font-size: var(--font-size-sm);
  cursor: pointer;
  transition: all var(--transition-bounce);
  box-shadow: var(--shadow-soft);
  color: var(--text-primary);
}

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

.diff-btn.active {
  color: var(--text-white);
}

.diff-btn[data-diff="easy"].active {
  background: linear-gradient(135deg, var(--color-accent-green), #55EFC4);
  border-color: var(--color-accent-green);
}

.diff-btn[data-diff="medium"].active {
  background: linear-gradient(135deg, var(--color-accent-orange), #F9CA24);
  border-color: var(--color-accent-orange);
}

.diff-btn[data-diff="hard"].active {
  background: linear-gradient(135deg, var(--color-accent-red), #E17055);
  border-color: var(--color-accent-red);
}

/* ---------- Problem Card ---------- */
.problem-card {
  background: var(--bg-card);
  backdrop-filter: blur(20px);
  border-radius: var(--radius-lg);
  padding: var(--space-2xl) var(--space-xl);
  text-align: center;
  box-shadow: var(--shadow-medium);
  margin-bottom: var(--space-lg);
  position: relative;
  overflow: hidden;
  transition: all var(--transition-smooth);
}

.problem-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
  background: linear-gradient(90deg, var(--color-primary), var(--color-accent-pink), var(--color-accent-orange), var(--color-accent-green), var(--color-accent-blue));
  background-size: 300% 100%;
  animation: gradientShift 3s ease-in-out infinite;
}

.problem-label {
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 2px;
  margin-bottom: var(--space-md);
}

.problem-text {
  font-family: var(--font-display);
  font-size: var(--font-size-4xl);
  color: var(--text-primary);
  margin-bottom: var(--space-lg);
  letter-spacing: 4px;
  transition: all var(--transition-smooth);
}

.problem-text .operator {
  color: var(--color-primary);
  margin: 0 var(--space-sm);
}

.problem-text .equals {
  color: var(--color-accent-pink);
  margin: 0 var(--space-sm);
}

.problem-text .question-mark {
  color: var(--color-accent-orange);
  animation: pulse 1.5s ease-in-out infinite;
}

.answer-container {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: var(--space-md);
  flex-wrap: wrap;
}

.answer-input {
  font-family: var(--font-display);
  font-size: var(--font-size-3xl);
  text-align: center;
  width: 180px;
  padding: var(--space-sm) var(--space-md);
  border: 3px solid var(--text-light);
  border-radius: var(--radius-md);
  background: transparent;
  color: var(--text-primary);
  outline: none;
  transition: all var(--transition-smooth);
  -moz-appearance: textfield;
}

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

.answer-input:focus {
  border-color: var(--color-primary);
  box-shadow: 0 0 0 4px rgba(108, 92, 231, 0.2);
}

.answer-input.correct {
  border-color: var(--color-accent-green);
  box-shadow: 0 0 0 4px rgba(0, 184, 148, 0.2);
  animation: correctPop 0.5s ease-out;
}

.answer-input.wrong {
  border-color: var(--color-accent-red);
  box-shadow: 0 0 0 4px rgba(255, 107, 107, 0.2);
  animation: shake 0.5s ease-out;
}

.btn-submit {
  background: linear-gradient(135deg, var(--color-accent-green), var(--color-accent-teal));
  color: var(--text-white);
  font-family: var(--font-display);
  font-size: var(--font-size-lg);
  padding: var(--space-sm) var(--space-lg);
  border: none;
  border-radius: var(--radius-lg);
  cursor: pointer;
  box-shadow: var(--shadow-soft);
  transition: all var(--transition-bounce);
}

.btn-submit:hover {
  transform: translateY(-3px) scale(1.05);
  box-shadow: var(--shadow-medium);
}

.btn-submit:active {
  transform: translateY(0) scale(0.97);
}

/* ---------- Feedback ---------- */
.feedback {
  margin-top: var(--space-lg);
  font-family: var(--font-display);
  font-size: var(--font-size-xl);
  min-height: 40px;
  transition: all var(--transition-smooth);
  opacity: 0;
  transform: translateY(10px);
}

.feedback.show {
  opacity: 1;
  transform: translateY(0);
}

.feedback.correct {
  color: var(--color-accent-green);
}

.feedback.wrong {
  color: var(--color-accent-red);
}

/* ---------- Progress Bar ---------- */
.progress-container {
  margin-bottom: var(--space-lg);
}

.progress-label {
  display: flex;
  justify-content: space-between;
  font-size: var(--font-size-sm);
  font-weight: 700;
  color: var(--text-secondary);
  margin-bottom: var(--space-xs);
}

.progress-bar {
  height: 12px;
  background: rgba(108, 92, 231, 0.1);
  border-radius: 100px;
  overflow: hidden;
  position: relative;
}

.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--color-primary), var(--color-accent-pink));
  border-radius: 100px;
  transition: width var(--transition-smooth);
  position: relative;
}

.progress-fill::after {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.3), transparent);
  animation: shimmer 2s ease-in-out infinite;
}

/* ---------- Back Button ---------- */
.btn-back {
  background: var(--bg-card);
  backdrop-filter: blur(12px);
  border: 2px solid transparent;
  border-radius: var(--radius-lg);
  padding: var(--space-sm) var(--space-md);
  font-family: var(--font-body);
  font-weight: 700;
  font-size: var(--font-size-md);
  cursor: pointer;
  transition: all var(--transition-bounce);
  box-shadow: var(--shadow-soft);
  color: var(--text-secondary);
  margin-bottom: var(--space-lg);
  display: inline-flex;
  align-items: center;
  gap: var(--space-xs);
}

.btn-back:hover {
  transform: translateX(-4px);
  color: var(--color-primary);
  border-color: var(--color-primary);
}

/* ---------- Confetti Canvas ---------- */
#confetti-canvas {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
  z-index: 999;
}

/* ---------- Keyframe Animations ---------- */
@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(30px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes bounce {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(-15px); }
}

@keyframes float {
  0%, 100% { transform: translate(0, 0) rotate(0deg); }
  25% { transform: translate(30px, -30px) rotate(5deg); }
  50% { transform: translate(-20px, 20px) rotate(-5deg); }
  75% { transform: translate(15px, 10px) rotate(3deg); }
}

@keyframes gradientShift {
  0%, 100% { background-position: 0% 50%; }
  50% { background-position: 100% 50%; }
}

@keyframes pulse {
  0%, 100% { opacity: 1; transform: scale(1); }
  50% { opacity: 0.6; transform: scale(1.1); }
}

@keyframes wiggle {
  0%, 100% { transform: rotate(0); }
  25% { transform: rotate(-10deg); }
  75% { transform: rotate(10deg); }
}

@keyframes shake {
  0%, 100% { transform: translateX(0); }
  10%, 50%, 90% { transform: translateX(-6px); }
  30%, 70% { transform: translateX(6px); }
}

@keyframes correctPop {
  0% { transform: scale(1); }
  50% { transform: scale(1.08); }
  100% { transform: scale(1); }
}

@keyframes shimmer {
  0% { transform: translateX(-100%); }
  100% { transform: translateX(100%); }
}

@keyframes popIn {
  0% {
    opacity: 0;
    transform: scale(0.5) translateY(20px);
  }
  70% {
    transform: scale(1.1) translateY(-5px);
  }
  100% {
    opacity: 1;
    transform: scale(1) translateY(0);
  }
}

/* ---------- Footer ---------- */
.footer {
  text-align: center;
  padding: var(--space-xl) 0 var(--space-lg);
  color: var(--text-light);
  font-size: var(--font-size-sm);
  font-weight: 600;
}

.footer .heart {
  color: var(--color-accent-pink);
  animation: pulse 1.5s ease-in-out infinite;
  display: inline-block;
}

/* ---------- Responsive ---------- */
@media (max-width: 768px) {
  .hero h1 {
    font-size: var(--font-size-3xl);
  }

  .stats-bar {
    grid-template-columns: repeat(2, 1fr);
  }

  .problem-text {
    font-size: var(--font-size-3xl);
    letter-spacing: 2px;
  }

  .answer-input {
    font-size: var(--font-size-2xl);
    width: 140px;
  }

  .hero-mascot {
    width: 110px;
    height: 110px;
  }
}

@media (max-width: 480px) {
  .hero h1 {
    font-size: var(--font-size-2xl);
  }

  .stats-bar {
    grid-template-columns: repeat(2, 1fr);
    gap: var(--space-xs);
  }

  .stat-card {
    padding: var(--space-sm);
  }

  .stat-card .stat-value {
    font-size: var(--font-size-xl);
  }

  .problem-text {
    font-size: var(--font-size-2xl);
  }

  .answer-input {
    width: 120px;
    font-size: var(--font-size-xl);
  }

  .controls-bar {
    gap: var(--space-xs);
  }

  .op-btn, .diff-btn {
    padding: var(--space-xs) var(--space-sm);
    font-size: var(--font-size-sm);
  }
}

/* ---------- Utility ---------- */
.hidden { display: none !important; }
.text-center { text-align: center; }

/* Number animation on stat change */
.stat-value.animate {
  animation: popIn 0.4s ease-out;
}

/* Streak fire */
.streak-fire {
  display: inline-block;
  animation: wiggle 0.5s ease-in-out infinite;
}