/* ===========================================
   Không Gian AI | Toán học - Design System & Main Styles
   Website học Toán trực quan cho cấp 3 & đại học
   =========================================== */

/* ============ CSS VARIABLES ============ */
:root {
  /* Colors - Light Mode */
  --primary: #6366f1;
  --primary-light: #818cf8;
  --primary-dark: #4f46e5;
  --secondary: #8b5cf6;
  --accent: #06b6d4;
  --accent-light: #22d3ee;

  --background: #f8fafc;
  --surface: #ffffff;
  --surface-elevated: #ffffff;
  --text: #1e293b;
  --text-secondary: #64748b;
  --text-muted: #94a3b8;
  --border: #e2e8f0;

  /* Gradients */
  --gradient-primary: linear-gradient(135deg, #6366f1 0%, #8b5cf6 100%);
  --gradient-accent: linear-gradient(135deg, #06b6d4 0%, #6366f1 100%);
  --gradient-hero: linear-gradient(135deg, #667eea 0%, #764ba2 100%);

  /* Shadows */
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
  --shadow: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
  --shadow-md: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
  --shadow-lg: 0 20px 25px -5px rgb(0 0 0 / 0.1), 0 8px 10px -6px rgb(0 0 0 / 0.1);
  --shadow-glow: 0 0 40px rgb(99 102 241 / 0.3);

  /* Typography */
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', monospace;

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

  /* Border Radius */
  --radius-sm: 0.375rem;
  --radius: 0.5rem;
  --radius-md: 0.75rem;
  --radius-lg: 1rem;
  --radius-xl: 1.5rem;
  --radius-full: 9999px;

  /* Transitions */
  --transition-fast: 150ms ease;
  --transition: 200ms ease;
  --transition-slow: 300ms ease;
}

/* Dark Mode */
[data-theme="dark"] {
  --background: #0f172a;
  --surface: #1e293b;
  --surface-elevated: #334155;
  --text: #f1f5f9;
  --text-secondary: #cbd5e1;
  --text-muted: #94a3b8;
  --border: #334155;
  --shadow-glow: 0 0 40px rgb(99 102 241 / 0.4);
}

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

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

body {
  font-family: var(--font-sans);
  background-color: var(--background);
  color: var(--text);
  line-height: 1.6;
  min-height: 100vh;
  transition: background-color var(--transition), color var(--transition);
}

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

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

img {
  max-width: 100%;
  height: auto;
  display: block;
}

/* ============ TYPOGRAPHY ============ */
h1,
h2,
h3,
h4,
h5,
h6 {
  font-weight: 700;
  line-height: 1.3;
  color: var(--text);
}

h1 {
  font-size: 2.5rem;
}

h2 {
  font-size: 2rem;
}

h3 {
  font-size: 1.5rem;
}

h4 {
  font-size: 1.25rem;
}

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

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

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

/* ============ HEADER & NAVIGATION ============ */
.header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  backdrop-filter: blur(10px);
  background-color: rgb(255 255 255 / 0.9);
}

[data-theme="dark"] .header {
  background-color: rgb(30 41 59 / 0.9);
}

.nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 70px;
}

.logo {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-size: 1.5rem;
  font-weight: 800;
  background: var(--gradient-primary);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.logo-icon {
  font-size: 1.75rem;
}

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

.nav-link {
  color: var(--text-secondary);
  font-weight: 500;
  padding: var(--space-sm) 0;
  position: relative;
  transition: color var(--transition);
}

.nav-link::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 0;
  height: 2px;
  background: var(--gradient-primary);
  transition: width var(--transition);
}

.nav-link:hover,
.nav-link.active {
  color: var(--primary);
}

.nav-link:hover::after,
.nav-link.active::after {
  width: 100%;
}

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

/* Theme Toggle Button */
.theme-toggle {
  background: var(--surface-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius-full);
  width: 44px;
  height: 44px;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  font-size: 1.25rem;
  transition: all var(--transition);
}

.theme-toggle:hover {
  background: var(--primary);
  border-color: var(--primary);
  color: white;
  transform: rotate(15deg);
}

/* Mobile Menu */
.mobile-menu-btn {
  display: none;
  background: none;
  border: none;
  font-size: 1.5rem;
  cursor: pointer;
  color: var(--text);
}

/* ============ HERO SECTION ============ */
.hero {
  min-height: 100vh;
  display: flex;
  align-items: center;
  padding-top: 70px;
  background: var(--background);
  position: relative;
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  top: -50%;
  right: -30%;
  width: 80%;
  height: 150%;
  background: var(--gradient-primary);
  opacity: 0.05;
  border-radius: 50%;
  filter: blur(100px);
}

.hero-content {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-3xl);
  align-items: center;
}

.hero-text {
  z-index: 1;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  background: var(--gradient-primary);
  color: white;
  padding: var(--space-xs) var(--space-md);
  border-radius: var(--radius-full);
  font-size: 0.875rem;
  font-weight: 600;
  margin-bottom: var(--space-lg);
  animation: pulse 2s infinite;
}

@keyframes pulse {

  0%,
  100% {
    opacity: 1;
  }

  50% {
    opacity: 0.8;
  }
}

.hero-title {
  font-size: 3.5rem;
  font-weight: 800;
  line-height: 1.1;
  margin-bottom: var(--space-lg);
}

.hero-title .highlight {
  background: var(--gradient-primary);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero-description {
  font-size: 1.25rem;
  color: var(--text-secondary);
  margin-bottom: var(--space-xl);
  max-width: 500px;
}

.hero-buttons {
  display: flex;
  gap: var(--space-md);
  flex-wrap: wrap;
}

.hero-visual {
  position: relative;
  z-index: 1;
}

.hero-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-xl);
  padding: var(--space-xl);
  box-shadow: var(--shadow-lg);
  position: relative;
}

.hero-card::before {
  content: '';
  position: absolute;
  inset: -2px;
  background: var(--gradient-primary);
  border-radius: var(--radius-xl);
  z-index: -1;
  opacity: 0;
  transition: opacity var(--transition);
}

.hero-card:hover::before {
  opacity: 1;
}

.formula-showcase {
  text-align: center;
}

.formula-showcase h3 {
  color: var(--text-muted);
  font-size: 0.875rem;
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: var(--space-lg);
}

.formula-item {
  background: var(--background);
  border-radius: var(--radius-lg);
  padding: var(--space-lg);
  margin-bottom: var(--space-md);
  border: 1px solid var(--border);
  transition: all var(--transition);
}

.formula-item:hover {
  border-color: var(--primary);
  transform: translateX(5px);
}

.formula-item .katex {
  font-size: 1.5rem !important;
}

.formula-name {
  font-size: 0.75rem;
  color: var(--text-muted);
  margin-top: var(--space-sm);
}

/* ============ BUTTONS ============ */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-sm);
  padding: var(--space-md) var(--space-xl);
  font-size: 1rem;
  font-weight: 600;
  border-radius: var(--radius-lg);
  border: none;
  cursor: pointer;
  transition: all var(--transition);
  text-decoration: none;
}

.btn-primary {
  background: var(--gradient-primary);
  color: white;
  box-shadow: 0 4px 15px rgb(99 102 241 / 0.4);
}

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 25px rgb(99 102 241 / 0.5);
  color: white;
}

.btn-secondary {
  background: var(--surface);
  color: var(--text);
  border: 1px solid var(--border);
}

.btn-secondary:hover {
  background: var(--surface-elevated);
  border-color: var(--primary);
  color: var(--primary);
}

/* ============ TOPICS SECTION ============ */
.topics {
  background: var(--background);
}

.section-header {
  text-align: center;
  max-width: 600px;
  margin: 0 auto var(--space-3xl);
}

.section-title {
  font-size: 2.5rem;
  margin-bottom: var(--space-md);
}

.section-subtitle {
  font-size: 1.125rem;
  color: var(--text-secondary);
}

.topics-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: var(--space-xl);
}

.topic-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-xl);
  padding: var(--space-xl);
  text-decoration: none;
  position: relative;
  overflow: hidden;
  transition: all var(--transition);
}

.topic-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
  background: var(--gradient-primary);
  transform: scaleX(0);
  transition: transform var(--transition);
}

.topic-card:hover {
  transform: translateY(-5px);
  box-shadow: var(--shadow-lg);
  border-color: var(--primary);
}

.topic-card:hover::before {
  transform: scaleX(1);
}

.topic-icon {
  width: 60px;
  height: 60px;
  background: var(--gradient-primary);
  border-radius: var(--radius-lg);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.75rem;
  margin-bottom: var(--space-lg);
  color: white;
}

.topic-title {
  font-size: 1.25rem;
  margin-bottom: var(--space-sm);
  color: var(--text);
}

.topic-description {
  color: var(--text-secondary);
  font-size: 0.9375rem;
  margin-bottom: var(--space-md);
}

.topic-count {
  font-size: 0.875rem;
  color: var(--primary);
  font-weight: 600;
}

/* ============ FEATURES SECTION ============ */
.features {
  background: var(--surface);
}

.features-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-xl);
}

.feature-card {
  text-align: center;
  padding: var(--space-xl);
}

.feature-icon {
  width: 80px;
  height: 80px;
  margin: 0 auto var(--space-lg);
  background: var(--background);
  border-radius: var(--radius-xl);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 2rem;
  transition: all var(--transition);
}

.feature-card:hover .feature-icon {
  background: var(--gradient-primary);
  transform: scale(1.1) rotate(5deg);
}

.feature-title {
  font-size: 1.125rem;
  margin-bottom: var(--space-sm);
}

.feature-description {
  color: var(--text-secondary);
  font-size: 0.9375rem;
}

/* ============ CTA SECTION ============ */
.cta {
  background: var(--gradient-hero);
  color: white;
  text-align: center;
  position: relative;
  overflow: hidden;
}

.cta::before {
  content: '';
  position: absolute;
  top: -50%;
  left: -20%;
  width: 60%;
  height: 200%;
  background: rgba(255, 255, 255, 0.1);
  border-radius: 50%;
  filter: blur(80px);
}

.cta-content {
  position: relative;
  z-index: 1;
}

.cta h2 {
  color: white;
  font-size: 2.5rem;
  margin-bottom: var(--space-md);
}

.cta p {
  color: rgba(255, 255, 255, 0.9);
  font-size: 1.125rem;
  margin-bottom: var(--space-xl);
}

.cta .btn-primary {
  background: white;
  color: var(--primary);
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.2);
}

.cta .btn-primary:hover {
  background: var(--background);
}

/* ============ FOOTER ============ */
.footer {
  background: var(--surface);
  border-top: 1px solid var(--border);
  padding: var(--space-3xl) 0 var(--space-xl);
}

.footer-content {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1fr;
  gap: var(--space-3xl);
  margin-bottom: var(--space-3xl);
}

.footer-brand {
  max-width: 300px;
}

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

.footer-brand p {
  color: var(--text-secondary);
  font-size: 0.9375rem;
}

.footer-title {
  font-size: 1rem;
  font-weight: 600;
  margin-bottom: var(--space-lg);
  color: var(--text);
}

.footer-links {
  list-style: none;
}

.footer-links li {
  margin-bottom: var(--space-sm);
}

.footer-links a {
  color: var(--text-secondary);
  font-size: 0.9375rem;
  transition: color var(--transition);
}

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

.footer-bottom {
  text-align: center;
  padding-top: var(--space-xl);
  border-top: 1px solid var(--border);
  color: var(--text-muted);
  font-size: 0.875rem;
}

/* ============ CONTENT PAGE STYLES ============ */
.page-header {
  padding: calc(70px + var(--space-3xl)) 0 var(--space-3xl);
  background: var(--gradient-primary);
  color: white;
  text-align: center;
  position: relative;
  overflow: hidden;
}

.page-header::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: url("data:image/svg+xml,%3Csvg width='60' height='60' viewBox='0 0 60 60' xmlns='http://www.w3.org/2000/svg'%3E%3Cg fill='none' fill-rule='evenodd'%3E%3Cg fill='%23ffffff' fill-opacity='0.05'%3E%3Cpath d='M36 34v-4h-2v4h-4v2h4v4h2v-4h4v-2h-4zm0-30V0h-2v4h-4v2h4v4h2V6h4V4h-4zM6 34v-4H4v4H0v2h4v4h2v-4h4v-2H6zM6 4V0H4v4H0v2h4v4h2V6h4V4H6z'/%3E%3C/g%3E%3C/g%3E%3C/svg%3E");
}

.page-header h1 {
  color: white;
  font-size: 3rem;
  position: relative;
  z-index: 1;
}

.page-header p {
  color: rgba(255, 255, 255, 0.9);
  font-size: 1.125rem;
  margin-top: var(--space-md);
  position: relative;
  z-index: 1;
}

.breadcrumb {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  justify-content: center;
  margin-top: var(--space-lg);
  position: relative;
  z-index: 1;
}

.breadcrumb a {
  color: rgba(255, 255, 255, 0.8);
}

.breadcrumb a:hover {
  color: white;
}

.breadcrumb span {
  color: rgba(255, 255, 255, 0.6);
}

/* Content Section */
.content-section {
  padding: var(--space-3xl) 0;
}

.formula-grid {
  display: grid;
  gap: var(--space-xl);
}

.formula-category {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-xl);
  overflow: hidden;
}

.formula-category-header {
  background: var(--gradient-primary);
  color: white;
  padding: var(--space-lg) var(--space-xl);
  display: flex;
  align-items: center;
  gap: var(--space-md);
}

.formula-category-header h2 {
  color: white;
  font-size: 1.25rem;
}

.formula-category-body {
  padding: var(--space-xl);
}

.formula-box {
  background: var(--background);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  margin-bottom: var(--space-lg);
  transition: all var(--transition);
}

.formula-box:last-child {
  margin-bottom: 0;
}

.formula-box:hover {
  border-color: var(--primary);
  box-shadow: var(--shadow-md);
}

.formula-box h3 {
  font-size: 1.125rem;
  margin-bottom: var(--space-md);
  display: flex;
  align-items: center;
  gap: var(--space-sm);
}

.formula-box h3::before {
  content: '📐';
  font-size: 1.25rem;
}

.formula-display {
  background: var(--surface);
  border-radius: var(--radius);
  padding: var(--space-lg);
  text-align: center;
  margin-bottom: var(--space-md);
  border: 1px dashed var(--border);
}

.formula-display .katex {
  font-size: 1.5rem !important;
}

.formula-note {
  color: var(--text-secondary);
  font-size: 0.9375rem;
  line-height: 1.7;
}

.formula-note strong {
  color: var(--text);
}

/* Theorem Box */
.theorem-box {
  background: linear-gradient(135deg, rgb(99 102 241 / 0.05) 0%, rgb(139 92 246 / 0.05) 100%);
  border-left: 4px solid var(--primary);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  margin-bottom: var(--space-lg);
}

.theorem-box h4 {
  color: var(--primary);
  margin-bottom: var(--space-md);
  font-size: 1rem;
}

/* Example Box */
.example-box {
  background: linear-gradient(135deg, rgb(6 182 212 / 0.05) 0%, rgb(99 102 241 / 0.05) 100%);
  border-left: 4px solid var(--accent);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  margin-top: var(--space-lg);
}

.example-box h4 {
  color: var(--accent);
  margin-bottom: var(--space-md);
  font-size: 1rem;
}

/* ============ RESPONSIVE ============ */
@media (max-width: 1024px) {
  .hero-content {
    grid-template-columns: 1fr;
    text-align: center;
  }

  .hero-description {
    margin-left: auto;
    margin-right: auto;
  }

  .hero-buttons {
    justify-content: center;
  }

  .hero-visual {
    display: none;
  }

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

  .footer-content {
    grid-template-columns: 1fr 1fr;
    gap: var(--space-xl);
  }
}

@media (max-width: 768px) {
  html {
    font-size: 14px;
  }

  .nav-links {
    display: none;
  }

  .mobile-menu-btn {
    display: block;
  }

  .hero-title {
    font-size: 2.5rem;
  }

  .section-title {
    font-size: 2rem;
  }

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

  .footer-content {
    grid-template-columns: 1fr;
    text-align: center;
  }

  .footer-brand {
    max-width: 100%;
  }
}

/* ============ ANIMATIONS ============ */
@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }

  to {
    opacity: 1;
    transform: translateY(0);
  }
}

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

.animate-delay-1 {
  animation-delay: 0.1s;
}

.animate-delay-2 {
  animation-delay: 0.2s;
}

.animate-delay-3 {
  animation-delay: 0.3s;
}

.animate-delay-4 {
  animation-delay: 0.4s;
}

/* Floating animation for decorative elements */
@keyframes float {

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

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

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