/* ============================================
   Even (大小) — Design System
   Matches app's Duolingo-inspired theme
   ============================================ */

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

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

body {
  font-family: 'Noto Sans SC', 'PingFang SC', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  font-size: var(--font-size-base);
  line-height: 1.6;
  color: var(--text-primary);
  background: var(--bg);
  transition: background var(--transition-normal), color var(--transition-normal);
  -webkit-font-smoothing: antialiased;
}

img { max-width: 100%; display: block; }
a { color: inherit; text-decoration: none; }
button { font: inherit; cursor: pointer; border: none; background: none; }
ul { list-style: none; }

/* --- CSS Custom Properties --- */
:root {
  /* Primary palette */
  --primary: #58CC02;
  --primary-dark: #46A302;
  --primary-light: #78E82C;
  --primary-pale: #D7FFB8;

  /* Accent */
  --gold: #FFB300;
  --gold-light: #FFD54F;
  --gold-dark: #FF8F00;
  --warm-orange: #FF7E50;
  --warm-pink: #FF7E8B;
  --sky-blue: #4DD0E1;

  /* Semantic */
  --success: #58CC02;
  --warning: #FF9800;
  --danger: #EF5350;
  --info: #42A5F5;

  /* Light mode surfaces */
  --bg: #FFFFFF;
  --bg-green: #F0FFF0;
  --surface: #FFFFFF;
  --card: #FFFFFF;
  --text-primary: #1C1C1C;
  --text-secondary: #8E8E93;
  --divider: #E5E5EA;

  /* Shadows */
  --shadow-card: 0 2px 8px rgba(0,0,0,0.09);
  --shadow-elevated: 0 4px 16px rgba(0,0,0,0.12);
  --shadow-button: 0 4px 12px rgba(88,204,2,0.19);
  --shadow-glow: 0 0 24px rgba(88,204,2,0.25);

  /* Spacing scale */
  --spacing-xs: 4px;
  --spacing-sm: 8px;
  --spacing-md: 16px;
  --spacing-lg: 24px;
  --spacing-xl: 32px;
  --spacing-xxl: 48px;
  --spacing-3xl: 64px;
  --spacing-4xl: 96px;

  /* Border radius */
  --radius-sm: 8px;
  --radius-md: 16px;
  --radius-lg: 24px;
  --radius-full: 9999px;

  /* Typography */
  --font-size-xs: 12px;
  --font-size-sm: 14px;
  --font-size-base: 16px;
  --font-size-lg: 18px;
  --font-size-xl: 24px;
  --font-size-2xl: 32px;
  --font-size-3xl: 48px;
  --font-size-hero: 64px;

  /* Font weights */
  --font-normal: 400;
  --font-medium: 500;
  --font-semibold: 600;
  --font-bold: 700;
  --font-extrabold: 800;

  /* Transitions */
  --transition-fast: 0.2s ease;
  --transition-normal: 0.3s ease;
  --transition-slow: 0.5s ease;

  /* Gradients */
  --gradient-green: linear-gradient(135deg, #58CC02, #46A302);
  --gradient-gold: linear-gradient(135deg, #FFD54F, #FFB300);
  --gradient-streak: linear-gradient(135deg, #FF9800, #FF5722);
  --gradient-symmetry: linear-gradient(135deg, #4DD0E1, #42A5F5);
  --gradient-hero: linear-gradient(160deg, #F0FFF0 0%, #FFFFFF 50%, #F0FFF0 100%);
}

/* --- Dark Theme --- */
[data-theme="dark"] {
  --bg: #121212;
  --bg-green: #0a1a0a;
  --surface: #1E1E1E;
  --card: #252525;
  --text-primary: #E0E0E0;
  --text-secondary: #9E9E9E;
  --divider: #333333;
  --primary-pale: #1B3D0A;
  --shadow-card: 0 2px 8px rgba(0,0,0,0.3);
  --shadow-elevated: 0 4px 16px rgba(0,0,0,0.4);
  --shadow-button: 0 4px 12px rgba(88,204,2,0.3);
  --shadow-glow: 0 0 24px rgba(88,204,2,0.35);
  --gradient-hero: linear-gradient(160deg, #0a1a0a 0%, #121212 50%, #0a1a0a 100%);
}

/* --- Layout --- */
.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--spacing-lg);
}

.section {
  padding: var(--spacing-4xl) 0;
}

.section-title {
  font-size: var(--font-size-3xl);
  font-weight: var(--font-extrabold);
  text-align: center;
  margin-bottom: var(--spacing-md);
  color: var(--text-primary);
}

.section-subtitle {
  font-size: var(--font-size-lg);
  color: var(--text-secondary);
  text-align: center;
  max-width: 600px;
  margin: 0 auto var(--spacing-xxl);
}

/* --- Grid --- */
.grid-2 {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--spacing-lg);
}

.grid-3 {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--spacing-lg);
}

@media (max-width: 768px) {
  .grid-2, .grid-3 {
    grid-template-columns: 1fr;
  }
}

@media (min-width: 769px) and (max-width: 1024px) {
  .grid-3 {
    grid-template-columns: repeat(2, 1fr);
  }
}

/* --- Cards --- */
.card {
  background: var(--card);
  border-radius: var(--radius-lg);
  padding: var(--spacing-xl);
  box-shadow: var(--shadow-card);
  transition: transform var(--transition-fast), box-shadow var(--transition-fast);
}

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

/* --- Buttons --- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--spacing-sm);
  padding: 14px 28px;
  border-radius: var(--radius-md);
  font-weight: var(--font-bold);
  font-size: var(--font-size-base);
  letter-spacing: 0.5px;
  transition: all var(--transition-fast);
  white-space: nowrap;
}

.btn-primary {
  background: var(--gradient-green);
  color: #fff;
  box-shadow: var(--shadow-button);
}

.btn-primary:hover {
  filter: brightness(1.1);
  transform: translateY(-2px);
  box-shadow: var(--shadow-glow);
}

.btn-primary:active {
  transform: translateY(0);
}

.btn-outline {
  border: 2px solid var(--primary);
  color: var(--primary);
  background: transparent;
}

.btn-outline:hover {
  background: var(--primary);
  color: #fff;
}

.btn-lg {
  padding: 18px 40px;
  font-size: var(--font-size-lg);
  border-radius: var(--radius-md);
}

.btn-gold {
  background: var(--gradient-gold);
  color: #1C1C1C;
  box-shadow: 0 4px 12px rgba(255,179,0,0.3);
}

.btn-gold:hover {
  filter: brightness(1.1);
  transform: translateY(-2px);
}

/* --- Header / Nav --- */
.header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  background: rgba(255,255,255,0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--divider);
  transition: background var(--transition-normal), border-color var(--transition-normal);
}

[data-theme="dark"] .header {
  background: rgba(18,18,18,0.85);
}

.header .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}

.logo {
  font-size: var(--font-size-xl);
  font-weight: var(--font-extrabold);
  color: var(--primary);
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
}

.logo span {
  font-size: var(--font-size-xs);
  color: var(--text-secondary);
  font-weight: var(--font-normal);
}

.nav-links {
  display: flex;
  gap: var(--spacing-xl);
  align-items: center;
}

.nav-links a {
  font-size: var(--font-size-sm);
  font-weight: var(--font-medium);
  color: var(--text-secondary);
  transition: color var(--transition-fast);
}

.nav-links a:hover {
  color: var(--primary);
}

.nav-right {
  display: flex;
  align-items: center;
  gap: var(--spacing-md);
}

/* Theme toggle */
.theme-toggle {
  width: 40px;
  height: 40px;
  border-radius: var(--radius-full);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 20px;
  background: var(--bg-green);
  transition: background var(--transition-fast), transform var(--transition-fast);
  cursor: pointer;
  border: none;
}

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

[data-theme="dark"] .theme-toggle {
  background: var(--primary-pale);
}

/* Mobile menu */
.menu-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  width: 24px;
  cursor: pointer;
  background: none;
  border: none;
  padding: 4px;
}

.menu-toggle span {
  display: block;
  width: 100%;
  height: 2px;
  background: var(--text-primary);
  border-radius: 2px;
  transition: all var(--transition-fast);
}

.menu-toggle.active span:nth-child(1) {
  transform: rotate(45deg) translate(5px, 5px);
}

.menu-toggle.active span:nth-child(2) {
  opacity: 0;
}

.menu-toggle.active span:nth-child(3) {
  transform: rotate(-45deg) translate(5px, -5px);
}

@media (max-width: 768px) {
  .menu-toggle { display: flex; }

  .nav-links {
    position: fixed;
    top: 64px;
    left: 0;
    right: 0;
    background: var(--bg);
    flex-direction: column;
    padding: var(--spacing-lg);
    gap: var(--spacing-md);
    border-bottom: 1px solid var(--divider);
    transform: translateY(-100%);
    opacity: 0;
    transition: all var(--transition-normal);
    pointer-events: none;
  }

  .nav-links.open {
    transform: translateY(0);
    opacity: 1;
    pointer-events: all;
  }
}

/* --- Text Utilities --- */
.text-center { text-align: center; }
.text-primary { color: var(--primary); }
.text-secondary { color: var(--text-secondary); }
.text-gradient {
  background: var(--gradient-green);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

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

@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

@keyframes float {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(-12px); }
}

@keyframes pulse {
  0%, 100% { transform: scale(1); }
  50% { transform: scale(1.05); }
}

@keyframes shimmer {
  0% { background-position: -200% 0; }
  100% { background-position: 200% 0; }
}

.animate-fade-in-up {
  animation: fadeInUp 0.6s ease forwards;
  opacity: 0;
}

.animate-fade-in {
  animation: fadeIn 0.6s ease forwards;
  opacity: 0;
}

.animate-float {
  animation: float 3s ease-in-out infinite;
}

.animate-pulse {
  animation: pulse 2s ease-in-out infinite;
}

/* Stagger delays */
.delay-1 { animation-delay: 0.1s; }
.delay-2 { animation-delay: 0.2s; }
.delay-3 { animation-delay: 0.3s; }
.delay-4 { animation-delay: 0.4s; }
.delay-5 { animation-delay: 0.5s; }
.delay-6 { animation-delay: 0.6s; }

/* --- Footer --- */
.footer {
  background: var(--surface);
  border-top: 1px solid var(--divider);
  padding: var(--spacing-xxl) 0 var(--spacing-lg);
}

.footer-grid {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1fr;
  gap: var(--spacing-xl);
  margin-bottom: var(--spacing-xxl);
}

@media (max-width: 768px) {
  .footer-grid {
    grid-template-columns: 1fr;
    gap: var(--spacing-lg);
  }
}

.footer-brand .logo {
  margin-bottom: var(--spacing-md);
}

.footer-brand p {
  color: var(--text-secondary);
  font-size: var(--font-size-sm);
  max-width: 280px;
}

.footer-col h4 {
  font-size: var(--font-size-sm);
  font-weight: var(--font-bold);
  margin-bottom: var(--spacing-md);
  color: var(--text-primary);
}

.footer-col a {
  display: block;
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
  padding: var(--spacing-xs) 0;
  transition: color var(--transition-fast);
}

.footer-col a:hover {
  color: var(--primary);
}

.footer-bottom {
  text-align: center;
  padding-top: var(--spacing-lg);
  border-top: 1px solid var(--divider);
  font-size: var(--font-size-xs);
  color: var(--text-secondary);
}

/* --- Scrollbar --- */
::-webkit-scrollbar { width: 8px; }
::-webkit-scrollbar-track { background: var(--bg); }
::-webkit-scrollbar-thumb {
  background: var(--divider);
  border-radius: var(--radius-full);
}
::-webkit-scrollbar-thumb:hover { background: var(--text-secondary); }

/* --- Selection --- */
::selection {
  background: var(--primary-pale);
  color: var(--primary-dark);
}

/* --- Body offset for fixed header --- */
body { padding-top: 64px; }

/* ============================================
   HERO SECTION
   ============================================ */
#hero {
  background: var(--gradient-hero);
  padding: var(--spacing-4xl) 0 var(--spacing-xxl);
  min-height: 85vh;
  display: flex;
  align-items: center;
}

.hero-content {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--spacing-xxl);
  align-items: center;
  margin-bottom: var(--spacing-xxl);
}

.hero-badge {
  display: inline-block;
  padding: 6px 16px;
  background: var(--primary-pale);
  color: var(--primary-dark);
  border-radius: var(--radius-full);
  font-size: var(--font-size-sm);
  font-weight: var(--font-bold);
  margin-bottom: var(--spacing-lg);
  letter-spacing: 1px;
}

.hero-title {
  font-size: var(--font-size-hero);
  font-weight: var(--font-extrabold);
  line-height: 1.1;
  margin-bottom: var(--spacing-md);
}

.hero-title-cn {
  display: block;
  font-size: var(--font-size-3xl);
  color: var(--text-secondary);
  font-weight: var(--font-semibold);
  margin-top: var(--spacing-xs);
}

.hero-tagline {
  font-size: var(--font-size-xl);
  font-weight: var(--font-semibold);
  color: var(--text-primary);
  margin-bottom: var(--spacing-md);
}

.hero-desc {
  font-size: var(--font-size-lg);
  color: var(--text-secondary);
  line-height: 1.8;
  margin-bottom: var(--spacing-xl);
  max-width: 480px;
}

.hero-actions {
  display: flex;
  gap: var(--spacing-md);
  flex-wrap: wrap;
}

/* Hero visual */
.hero-visual {
  display: flex;
  justify-content: center;
  align-items: center;
}

.hero-mascot {
  position: relative;
}

.mascot-circle {
  width: 280px;
  height: 280px;
  border-radius: 50%;
  background: var(--gradient-green);
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: var(--shadow-glow);
  animation: float 3s ease-in-out infinite;
}

.mascot-emoji {
  font-size: 120px;
  filter: drop-shadow(0 4px 8px rgba(0,0,0,0.2));
}

.mascot-sparkles {
  position: absolute;
  inset: -20px;
}

.sparkle {
  position: absolute;
  font-size: 24px;
  animation: pulse 2s ease-in-out infinite;
}

.sparkle.s1 { top: 10%; left: 5%; animation-delay: 0s; }
.sparkle.s2 { top: 0%; right: 10%; animation-delay: 0.5s; }
.sparkle.s3 { bottom: 10%; left: 10%; animation-delay: 1s; }

/* Hero stats */
.hero-stats {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: var(--spacing-xl);
  padding: var(--spacing-xl) var(--spacing-xxl);
  background: var(--card);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-card);
}

.stat-item {
  text-align: center;
}

.stat-number {
  display: block;
  font-size: var(--font-size-2xl);
  font-weight: var(--font-extrabold);
  color: var(--primary);
}

.stat-label {
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
}

.stat-divider {
  width: 1px;
  height: 40px;
  background: var(--divider);
}

@media (max-width: 768px) {
  .hero-content {
    grid-template-columns: 1fr;
    text-align: center;
  }

  .hero-title { font-size: var(--font-size-3xl); }
  .hero-title-cn { font-size: var(--font-size-xl); }
  .hero-desc { max-width: 100%; }
  .hero-actions { justify-content: center; }
  .hero-visual { order: -1; }
  .mascot-circle { width: 180px; height: 180px; }
  .mascot-emoji { font-size: 80px; }
  .hero-stats { flex-direction: column; gap: var(--spacing-md); padding: var(--spacing-lg); }
  .stat-divider { width: 40px; height: 1px; }
}

/* ============================================
   FEATURES SECTION
   ============================================ */
.feature-card {
  text-align: center;
  padding: var(--spacing-xl) var(--spacing-lg);
}

.feature-icon {
  width: 72px;
  height: 72px;
  border-radius: var(--radius-lg);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 36px;
  margin: 0 auto var(--spacing-lg);
}

.feature-card h3 {
  font-size: var(--font-size-lg);
  font-weight: var(--font-bold);
  margin-bottom: var(--spacing-sm);
}

.feature-card p {
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
  line-height: 1.6;
}

.feature-icon.green { background: var(--primary-pale); }
.feature-icon.gold { background: #FFF8E1; }
.feature-icon.orange { background: #FFF3E0; }
.feature-icon.blue { background: #E0F7FA; }
.feature-icon.pink { background: #FCE4EC; }
.feature-icon.purple { background: #F3E5F5; }

[data-theme="dark"] .feature-icon.green { background: #1B3D0A; }
[data-theme="dark"] .feature-icon.gold { background: #3D2E00; }
[data-theme="dark"] .feature-icon.orange { background: #3D1F00; }
[data-theme="dark"] .feature-icon.blue { background: #003D3F; }
[data-theme="dark"] .feature-icon.pink { background: #3D0020; }
[data-theme="dark"] .feature-icon.purple { background: #2A003D; }

/* ============================================
   HOW IT WORKS SECTION
   ============================================ */
#how-it-works {
  background: var(--bg-green);
}

.steps-container {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--spacing-xl);
  position: relative;
}

.steps-container::before {
  content: '';
  position: absolute;
  top: 48px;
  left: calc(16.67% + 24px);
  right: calc(16.67% + 24px);
  height: 3px;
  background: var(--gradient-green);
  border-radius: 2px;
  z-index: 0;
}

.step-card {
  text-align: center;
  position: relative;
  z-index: 1;
}

.step-number {
  width: 96px;
  height: 96px;
  border-radius: 50%;
  background: var(--gradient-green);
  color: #fff;
  font-size: var(--font-size-2xl);
  font-weight: var(--font-extrabold);
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 0 auto var(--spacing-lg);
  box-shadow: var(--shadow-button);
  position: relative;
}

.step-number::after {
  content: '';
  position: absolute;
  inset: -6px;
  border-radius: 50%;
  border: 3px solid var(--primary-light);
  opacity: 0.3;
}

.step-card h3 {
  font-size: var(--font-size-lg);
  font-weight: var(--font-bold);
  margin-bottom: var(--spacing-sm);
}

.step-card p {
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
  line-height: 1.6;
  max-width: 240px;
  margin: 0 auto;
}

.step-icon {
  font-size: 28px;
  margin-bottom: var(--spacing-sm);
}

@media (max-width: 768px) {
  .steps-container {
    grid-template-columns: 1fr;
    gap: var(--spacing-xxl);
  }
  .steps-container::before {
    display: none;
  }
}

/* ============================================
   DOWNLOAD SECTION
   ============================================ */
#download {
  background: var(--gradient-hero);
}

.download-card {
  background: var(--card);
  border-radius: var(--radius-lg);
  padding: var(--spacing-xxl);
  box-shadow: var(--shadow-elevated);
  text-align: center;
  max-width: 640px;
  margin: 0 auto;
}

.download-card h2 {
  font-size: var(--font-size-2xl);
  font-weight: var(--font-extrabold);
  margin-bottom: var(--spacing-md);
}

.download-card .desc {
  color: var(--text-secondary);
  margin-bottom: var(--spacing-xl);
  font-size: var(--font-size-lg);
}

.download-btn-group {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--spacing-md);
  margin-bottom: var(--spacing-xl);
}

.download-info {
  display: flex;
  justify-content: center;
  gap: var(--spacing-xxl);
  padding-top: var(--spacing-lg);
  border-top: 1px solid var(--divider);
}

.download-info-item {
  text-align: center;
}

.download-info-item .label {
  font-size: var(--font-size-xs);
  color: var(--text-secondary);
  display: block;
  margin-bottom: var(--spacing-xs);
}

.download-info-item .value {
  font-size: var(--font-size-sm);
  font-weight: var(--font-bold);
  color: var(--text-primary);
}

.download-icon {
  font-size: 64px;
  margin-bottom: var(--spacing-lg);
}

/* ============================================
   FOOTER
   ============================================ */
.footer-brand .logo {
  font-size: var(--font-size-xl);
}

.footer-social {
  display: flex;
  gap: var(--spacing-sm);
  margin-top: var(--spacing-md);
}

.footer-social a {
  width: 36px;
  height: 36px;
  border-radius: var(--radius-full);
  background: var(--bg-green);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 16px;
  transition: background var(--transition-fast), transform var(--transition-fast);
}

.footer-social a:hover {
  background: var(--primary-pale);
  transform: translateY(-2px);
}