/* ==========================================
   DESIGN SYSTEM - Website Học Toán Tiền Tiểu Học
   ========================================== */

/* Import Google Fonts */
@import url('https://fonts.googleapis.com/css2?family=Fredoka:wght@400;500;600;700&family=Inter:wght@400;500;600;700&display=swap');

/* ==========================================
   CSS VARIABLES
   ========================================== */
:root {
  /* Colors - Vibrant & Child-friendly */
  --color-primary: #4F46E5;
  --color-primary-light: #818CF8;
  --color-primary-dark: #3730A3;

  --color-secondary: #F59E0B;
  --color-secondary-light: #FCD34D;
  --color-secondary-dark: #D97706;

  --color-accent-pink: #EC4899;
  --color-accent-green: #10B981;
  --color-accent-purple: #A855F7;
  --color-accent-blue: #06B6D4;

  --color-bg-primary: #FFFFFF;
  --color-bg-secondary: #F9FAFB;
  --color-bg-gradient: linear-gradient(135deg, #667EEA 0%, #764BA2 100%);
  --color-bg-soft: linear-gradient(to bottom, #FEF3C7, #FFFFFF);

  --color-text-primary: #1F2937;
  --color-text-secondary: #6B7280;
  --color-text-light: #9CA3AF;

  --color-border: #E5E7EB;
  --color-shadow: rgba(0, 0, 0, 0.1);

  /* Typography */
  --font-heading: 'Fredoka', sans-serif;
  --font-body: 'Inter', sans-serif;

  --font-size-xs: 0.75rem;
  --font-size-sm: 0.875rem;
  --font-size-base: 1rem;
  --font-size-lg: 1.125rem;
  --font-size-xl: 1.25rem;
  --font-size-2xl: 1.5rem;
  --font-size-3xl: 1.875rem;
  --font-size-4xl: 2.25rem;
  --font-size-5xl: 3rem;

  /* Spacing */
  --spacing-xs: 0.25rem;
  --spacing-sm: 0.5rem;
  --spacing-md: 1rem;
  --spacing-lg: 1.5rem;
  --spacing-xl: 2rem;
  --spacing-2xl: 3rem;
  --spacing-3xl: 4rem;

  /* Border Radius */
  --radius-sm: 0.5rem;
  --radius-md: 1rem;
  --radius-lg: 1.5rem;
  --radius-xl: 2rem;
  --radius-full: 9999px;

  /* Shadows */
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);

  /* Transitions */
  --transition-base: all 0.3s ease;
  --transition-fast: all 0.15s ease;
}

/* ==========================================
   RESET & BASE STYLES
   ========================================== */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  font-size: 16px;
}

body {
  font-family: var(--font-body);
  color: var(--color-text-primary);
  background-color: var(--color-bg-primary);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* ==========================================
   TYPOGRAPHY
   ========================================== */
h1,
h2,
h3,
h4,
h5,
h6 {
  font-family: var(--font-heading);
  font-weight: 700;
  line-height: 1.2;
  color: var(--color-text-primary);
  margin-bottom: var(--spacing-md);
}

h1 {
  font-size: var(--font-size-4xl);
}

h2 {
  font-size: var(--font-size-3xl);
}

h3 {
  font-size: var(--font-size-2xl);
}

h4 {
  font-size: var(--font-size-xl);
}

p {
  margin-bottom: var(--spacing-md);
  color: var(--color-text-secondary);
}

a {
  color: var(--color-primary);
  text-decoration: none;
  transition: var(--transition-base);
}

a:hover {
  color: var(--color-primary-dark);
}

/* ==========================================
   LAYOUT
   ========================================== */
.container {
  width: 100%;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--spacing-lg);
}

.section {
  padding: var(--spacing-3xl) 0;
}

.section-alt {
  background-color: var(--color-bg-secondary);
}

/* ==========================================
   NAVIGATION
   ========================================== */
.navbar {
  position: sticky;
  top: 0;
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(10px);
  box-shadow: var(--shadow-sm);
  z-index: 1000;
  padding: var(--spacing-md) 0;
}

.navbar .container {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.logo {
  font-family: var(--font-heading);
  font-size: var(--font-size-2xl);
  font-weight: 700;
  color: var(--color-primary);
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
}

.nav-links {
  display: flex;
  list-style: none;
  gap: var(--spacing-xl);
  align-items: center;
}

.nav-links a {
  font-weight: 500;
  color: var(--color-text-primary);
  padding: var(--spacing-sm) var(--spacing-md);
  border-radius: var(--radius-sm);
  transition: var(--transition-base);
}

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

.nav-links a.active {
  background-color: var(--color-primary);
  color: white;
  font-weight: 600;
}

.nav-toggle {
  display: none;
  flex-direction: column;
  gap: 4px;
  background: none;
  border: none;
  cursor: pointer;
}

.nav-toggle span {
  width: 25px;
  height: 3px;
  background-color: var(--color-primary);
  border-radius: var(--radius-full);
  transition: var(--transition-base);
}

/* ==========================================
   BUTTONS
   ========================================== */
.btn {
  display: inline-block;
  padding: var(--spacing-md) var(--spacing-xl);
  font-family: var(--font-heading);
  font-size: var(--font-size-base);
  font-weight: 600;
  text-align: center;
  border-radius: var(--radius-lg);
  cursor: pointer;
  transition: var(--transition-base);
  border: none;
  text-decoration: none;
}

.btn-primary {
  background: var(--color-primary);
  color: white;
  box-shadow: var(--shadow-md);
}

.btn-primary:hover {
  background: var(--color-primary-dark);
  transform: translateY(-2px);
  box-shadow: var(--shadow-lg);
}

.btn-secondary {
  background: var(--color-secondary);
  color: white;
  box-shadow: var(--shadow-md);
}

.btn-secondary:hover {
  background: var(--color-secondary-dark);
  transform: translateY(-2px);
  box-shadow: var(--shadow-lg);
}

.btn-large {
  padding: var(--spacing-lg) var(--spacing-2xl);
  font-size: var(--font-size-lg);
}

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

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

/* ==========================================
   CARDS
   ========================================== */
.card {
  background: white;
  border-radius: var(--radius-lg);
  padding: var(--spacing-xl);
  box-shadow: var(--shadow-md);
  transition: var(--transition-base);
  border: 1px solid var(--color-border);
}

.card:hover {
  transform: translateY(-5px);
  box-shadow: var(--shadow-xl);
}

.card-icon {
  width: 60px;
  height: 60px;
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: var(--font-size-3xl);
  margin-bottom: var(--spacing-md);
}

.card-title {
  font-size: var(--font-size-xl);
  margin-bottom: var(--spacing-sm);
}

.card-text {
  color: var(--color-text-secondary);
  margin-bottom: 0;
}

/* ==========================================
   HERO SECTION
   ========================================== */
.hero {
  padding: var(--spacing-3xl) 0;
  background: linear-gradient(135deg, #667EEA 0%, #764BA2 100%);
  color: white;
  text-align: center;
  position: relative;
  overflow: hidden;
  min-height: 600px;
  display: flex;
  align-items: center;
}

.hero::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: url('data:image/svg+xml,<svg width="100" height="100" xmlns="http://www.w3.org/2000/svg"><circle cx="50" cy="50" r="2" fill="rgba(255,255,255,0.1)"/></svg>');
  opacity: 0.3;
}

.hero .container {
  position: relative;
  z-index: 1;
  width: 100%;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
}

.hero h1 {
  color: white;
  font-size: var(--font-size-5xl);
  margin-bottom: var(--spacing-lg);
  text-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
  width: 100%;
}

.hero p {
  font-size: var(--font-size-xl);
  color: rgba(255, 255, 255, 0.95);
  margin-bottom: var(--spacing-2xl);
  max-width: 700px;
  margin-left: auto;
  margin-right: auto;
  line-height: 1.6;
}

.hero .btn {
  margin: 0 auto var(--spacing-2xl);
  display: inline-block;
  animation: pulse 2s ease-in-out infinite;
}

.hero-image {
  max-width: 500px;
  width: 100%;
  height: auto;
  margin: 0 auto;
  border-radius: var(--radius-xl);
  box-shadow: 0 10px 40px rgba(0, 0, 0, 0.3);
  transition: transform 0.3s ease;
}

.hero-image:hover {
  transform: scale(1.02);
}

/* ==========================================
   GRID LAYOUTS
   ========================================== */
.grid {
  display: grid;
  gap: var(--spacing-xl);
}

.grid-2 {
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
}

.grid-3 {
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
}

.grid-4 {
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
}

/* ==========================================
   LESSON COMPONENTS
   ========================================== */
.lesson-header {
  text-align: center;
  padding: var(--spacing-2xl) 0;
  background: linear-gradient(to right, #FEF3C7, #DBEAFE);
}

.lesson-objective {
  background: white;
  border-left: 4px solid var(--color-primary);
  padding: var(--spacing-lg);
  margin: var(--spacing-xl) 0;
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-sm);
}

.lesson-content {
  background: white;
  padding: var(--spacing-xl);
  border-radius: var(--radius-lg);
  margin-bottom: var(--spacing-xl);
}

.number-card {
  text-align: center;
  padding: var(--spacing-xl);
  background: linear-gradient(135deg, var(--color-primary-light), var(--color-primary));
  color: white;
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
  transition: var(--transition-base);
}

.number-card:hover {
  transform: scale(1.05) rotate(2deg);
}

.number-display {
  font-size: 5rem;
  font-weight: 700;
  font-family: var(--font-heading);
  margin: var(--spacing-md) 0;
}

.practice-section {
  background: var(--color-bg-secondary);
  padding: var(--spacing-xl);
  border-radius: var(--radius-lg);
  margin: var(--spacing-xl) 0;
}

.parent-tips {
  background: linear-gradient(135deg, #FEF3C7, #FECACA);
  padding: var(--spacing-xl);
  border-radius: var(--radius-lg);
  border-left: 4px solid var(--color-secondary);
}

/* ==========================================
   UTILITIES
   ========================================== */
.text-center {
  text-align: center;
}

.text-primary {
  color: var(--color-primary);
}

.bg-primary {
  background-color: var(--color-primary);
}

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

.bg-pink {
  background: linear-gradient(135deg, #FCA5A5, #EC4899);
}

.bg-green {
  background: linear-gradient(135deg, #6EE7B7, #10B981);
}

.bg-purple {
  background: linear-gradient(135deg, #C4B5FD, #A855F7);
}

.bg-blue {
  background: linear-gradient(135deg, #7DD3FC, #06B6D4);
}

.mb-sm {
  margin-bottom: var(--spacing-sm);
}

.mb-md {
  margin-bottom: var(--spacing-md);
}

.mb-lg {
  margin-bottom: var(--spacing-lg);
}

.mb-xl {
  margin-bottom: var(--spacing-xl);
}

.mt-sm {
  margin-top: var(--spacing-sm);
}

.mt-md {
  margin-top: var(--spacing-md);
}

.mt-lg {
  margin-top: var(--spacing-lg);
}

.mt-xl {
  margin-top: var(--spacing-xl);
}

/* ==========================================
   ANIMATIONS
   ========================================== */
@keyframes float {

  0%,
  100% {
    transform: translateY(0);
  }

  50% {
    transform: translateY(-10px);
  }
}

@keyframes pulse {

  0%,
  100% {
    transform: scale(1);
  }

  50% {
    transform: scale(1.05);
  }
}

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

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

/* ==========================================
   RESPONSIVE DESIGN
   ========================================== */
/* Tablet Responsive */
@media (max-width: 1024px) {
  .container {
    padding: 0 var(--spacing-xl);
  }

  .hero {
    min-height: 500px;
    padding: var(--spacing-2xl) 0;
  }

  .hero h1 {
    font-size: var(--font-size-4xl);
  }

  .hero-image {
    max-width: 400px;
  }
}

/* Mobile Responsive */
@media (max-width: 768px) {
  :root {
    --font-size-5xl: 2rem;
    --font-size-4xl: 1.75rem;
    --font-size-3xl: 1.5rem;
  }

  .nav-links {
    position: fixed;
    top: 70px;
    left: 0;
    right: 0;
    background: white;
    flex-direction: column;
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-lg);
    transform: translateY(-100%);
    opacity: 0;
    transition: var(--transition-base);
  }

  .nav-links.active {
    transform: translateY(0);
    opacity: 1;
  }

  .nav-toggle {
    display: flex;
  }

  .section {
    padding: var(--spacing-2xl) 0;
  }

  .grid-2,
  .grid-3,
  .grid-4 {
    grid-template-columns: 1fr;
  }

  .hero {
    min-height: 450px;
    padding: var(--spacing-xl) 0;
  }

  .hero h1 {
    font-size: var(--font-size-3xl);
    margin-bottom: var(--spacing-md);
  }

  .hero p {
    font-size: var(--font-size-base);
    margin-bottom: var(--spacing-lg);
  }

  .hero .btn {
    margin-bottom: var(--spacing-lg);
  }

  .hero-image {
    max-width: 100%;
  }

  .card {
    padding: var(--spacing-lg);
  }
}

/* Small Mobile Responsive */
@media (max-width: 480px) {
  .container {
    padding: 0 var(--spacing-md);
  }

  .hero {
    min-height: 400px;
  }

  .hero h1 {
    font-size: var(--font-size-2xl);
    line-height: 1.3;
  }

  .hero p {
    font-size: var(--font-size-sm);
  }

  .btn-large {
    padding: var(--spacing-md) var(--spacing-lg);
    font-size: var(--font-size-base);
    width: 100%;
    max-width: 300px;
  }

  .number-display {
    font-size: 3rem;
  }

  .hero-image {
    max-width: 100%;
    border-radius: var(--radius-md);
  }
}

/* ==========================================
   FOOTER
   ========================================== */
.footer {
  background: var(--color-text-primary);
  color: white;
  padding: var(--spacing-2xl) 0;
  text-align: center;
}

.footer p {
  color: rgba(255, 255, 255, 0.8);
  margin: 0;
}

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

.footer a:hover {
  color: white;
}