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

:root {
  /* Colors - Light Mode (default) */
  --color-primary: #1e40af;
  --color-primary-dark: #1e3a8a;
  --color-primary-light: #3b82f6;
  --color-secondary: #0ea5e9;
  --color-accent: #f59e0b;

  --color-text: #1f2937;
  --color-text-light: #6b7280;
  --color-text-inverse: #ffffff;

  --color-bg: #ffffff;
  --color-bg-alt: #f9fafb;
  --color-bg-dark: #1f2937;

  --color-border: #e5e7eb;
  --color-success: #10b981;
  --color-error: #ef4444;

  /* Hero gradient - Light */
  --hero-gradient: linear-gradient(135deg, #f0f9ff 0%, #e0f2fe 100%);
  --feature-icon-bg: #dbeafe;
  --chat-ai-bg: #f9fafb;

  /* Typography */
  --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen,
    Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
  --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: 2rem;
  --font-size-4xl: 2.5rem;
  --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;
  --spacing-4xl: 6rem;

  /* Border Radius */
  --radius-sm: 0.25rem;
  --radius-md: 0.5rem;
  --radius-lg: 1rem;
  --radius-full: 9999px;

  /* Shadows */
  --shadow-sm: 0 1px 2px 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-fast: 150ms ease;
  --transition-base: 200ms ease;
  --transition-slow: 300ms ease;

  /* Layout */
  --max-width: 1200px;
  --nav-height: 64px;
}

/* Dark Mode Colors */
[data-theme="dark"] {
  --color-primary: #3b82f6;
  --color-primary-dark: #2563eb;
  --color-primary-light: #60a5fa;
  --color-secondary: #38bdf8;
  --color-accent: #fbbf24;

  --color-text: #f3f4f6;
  --color-text-light: #9ca3af;
  --color-text-inverse: #111827;

  --color-bg: #111827;
  --color-bg-alt: #1f2937;
  --color-bg-dark: #0f172a;

  --color-border: #374151;
  --color-success: #34d399;
  --color-error: #f87171;

  /* Hero gradient - Dark */
  --hero-gradient: linear-gradient(135deg, #1e3a5f 0%, #1e293b 100%);
  --feature-icon-bg: #1e3a8a;
  --chat-ai-bg: #1f2937;

  /* Shadows - Dark mode */
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.4);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.4);
}

html {
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-family);
  font-size: var(--font-size-base);
  line-height: 1.6;
  color: var(--color-text);
  background: var(--color-bg);
}

/* Utility Classes */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--spacing-md);
}

.section-header {
  text-align: center;
  margin-bottom: var(--spacing-3xl);
}

.section-header h2 {
  font-size: var(--font-size-3xl);
  color: var(--color-text);
  margin-bottom: var(--spacing-sm);
}

.section-header p {
  font-size: var(--font-size-lg);
  color: var(--color-text-light);
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--spacing-sm);
  padding: var(--spacing-sm) var(--spacing-lg);
  font-size: var(--font-size-base);
  font-weight: 500;
  text-decoration: none;
  border-radius: var(--radius-md);
  border: 2px solid transparent;
  cursor: pointer;
  transition: all var(--transition-base);
}

.btn-sm {
  padding: var(--spacing-xs) var(--spacing-md);
  font-size: var(--font-size-sm);
}

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

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

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

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

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

/* Navigation */
.navbar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background: var(--color-bg);
  border-bottom: 1px solid var(--color-border);
  z-index: 1000;
  transition: box-shadow var(--transition-base);
}

.navbar.scrolled {
  box-shadow: var(--shadow-md);
}

.nav-container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--spacing-md);
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.logo {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  text-decoration: none;
  font-weight: 700;
  font-size: var(--font-size-xl);
}

.logo-icon {
  width: 32px;
  height: 32px;
  object-fit: contain;
}

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

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

.nav-links a {
  color: var(--color-text-light);
  text-decoration: none;
  font-weight: 500;
  transition: color var(--transition-fast);
}

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

/* Language Selector */
.language-selector {
  position: relative;
}

.lang-btn {
  display: flex;
  align-items: center;
  gap: var(--spacing-xs);
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--spacing-xs) var(--spacing-sm);
  cursor: pointer;
  font-size: var(--font-size-sm);
  font-weight: 500;
  color: var(--color-text);
  transition: all var(--transition-fast);
}

.lang-btn:hover {
  background: var(--color-bg);
  border-color: var(--color-primary-light);
}

.lang-flag {
  font-size: 1.1em;
}

.lang-code {
  font-weight: 600;
}

.lang-arrow {
  font-size: 0.7em;
  color: var(--color-text-light);
  transition: transform var(--transition-fast);
}

.lang-dropdown {
  position: absolute;
  top: 100%;
  right: 0;
  margin-top: var(--spacing-xs);
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-lg);
  min-width: 140px;
  opacity: 0;
  visibility: hidden;
  transform: translateY(-10px);
  transition: all var(--transition-fast);
  z-index: 1001;
}

.lang-dropdown.open {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.lang-option {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  width: 100%;
  padding: var(--spacing-sm) var(--spacing-md);
  background: none;
  border: none;
  cursor: pointer;
  font-size: var(--font-size-sm);
  color: var(--color-text);
  text-align: left;
  transition: background var(--transition-fast);
}

.lang-option:hover {
  background: var(--color-bg-alt);
}

.lang-option:first-child {
  border-radius: var(--radius-md) var(--radius-md) 0 0;
}

.lang-option:last-child {
  border-radius: 0 0 var(--radius-md) var(--radius-md);
}

/* Theme Toggle */
.theme-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-fast);
  position: relative;
}

.theme-toggle:hover {
  background: var(--color-bg);
  border-color: var(--color-primary-light);
}

.theme-icon {
  font-size: 1.25rem;
  transition: opacity var(--transition-fast), transform var(--transition-fast);
  position: absolute;
}

.theme-icon-light {
  opacity: 1;
  transform: scale(1);
  color: var(--color-accent);
}

.theme-icon-dark {
  opacity: 0;
  transform: scale(0.5);
  color: var(--color-primary-light);
}

[data-theme="dark"] .theme-icon-light {
  opacity: 0;
  transform: scale(0.5);
}

[data-theme="dark"] .theme-icon-dark {
  opacity: 1;
  transform: scale(1);
}

/* Dark mode footer overrides */
[data-theme="dark"] .footer {
  background: #0f172a;
}

[data-theme="dark"] .footer-brand .logo-text,
[data-theme="dark"] .footer-column a {
  color: #f3f4f6;
}

[data-theme="dark"] .footer-brand p,
[data-theme="dark"] .footer-column h4,
[data-theme="dark"] .footer-bottom .disclaimer {
  color: #9ca3af;
}

[data-theme="dark"] .footer-bottom .copyright {
  color: #6b7280;
}

[data-theme="dark"] .footer-column a:hover {
  color: #60a5fa;
}

.mobile-menu-btn {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: var(--spacing-sm);
}

.menu-icon {
  display: block;
  width: 24px;
  height: 2px;
  background: var(--color-text);
  position: relative;
}

.menu-icon::before,
.menu-icon::after {
  content: '';
  position: absolute;
  width: 24px;
  height: 2px;
  background: var(--color-text);
  left: 0;
}

.menu-icon::before {
  top: -8px;
}

.menu-icon::after {
  top: 8px;
}

/* Hero Section */
.hero {
  padding-top: calc(var(--nav-height) + var(--spacing-4xl));
  padding-bottom: var(--spacing-4xl);
  background: var(--hero-gradient);
}

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

.hero-content h1 {
  font-size: var(--font-size-5xl);
  line-height: 1.1;
  margin-bottom: var(--spacing-lg);
}

.hero-content .highlight {
  color: var(--color-primary);
}

.hero-subtitle {
  font-size: var(--font-size-xl);
  color: var(--color-text-light);
  margin-bottom: var(--spacing-xl);
}

.hero-cta {
  display: flex;
  gap: var(--spacing-md);
  margin-bottom: var(--spacing-lg);
}

.hero-note {
  font-size: var(--font-size-sm);
  color: var(--color-text-light);
}

.hero-note .check-icon {
  color: var(--color-success);
}

.hero-note .separator {
  margin: 0 var(--spacing-sm);
  color: var(--color-border);
}

/* Chat Preview */
.chat-preview {
  background: var(--color-bg);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-xl);
  overflow: hidden;
}

.chat-header {
  background: var(--color-bg-alt);
  padding: var(--spacing-sm) var(--spacing-md);
  display: flex;
  gap: var(--spacing-sm);
}

.chat-header .dot {
  width: 12px;
  height: 12px;
  border-radius: var(--radius-full);
}

.dot.red { background: #ef4444; }
.dot.yellow { background: #f59e0b; }
.dot.green { background: #10b981; }

.chat-body {
  padding: var(--spacing-lg);
  display: flex;
  flex-direction: column;
  gap: var(--spacing-md);
}

.chat-message {
  padding: var(--spacing-md);
  border-radius: var(--radius-md);
  max-width: 90%;
}

.chat-message.user {
  background: var(--color-primary);
  color: var(--color-text-inverse);
  align-self: flex-end;
}

.chat-message.ai {
  background: var(--chat-ai-bg);
  align-self: flex-start;
}

.chat-message p {
  margin-bottom: var(--spacing-sm);
}

.chat-message ul {
  margin-left: var(--spacing-lg);
  margin-bottom: var(--spacing-sm);
}

.chat-message .citation {
  font-size: var(--font-size-sm);
  color: var(--color-primary);
  font-style: italic;
}

/* Features Section */
.features {
  padding: var(--spacing-4xl) 0;
}

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

.feature-card {
  background: var(--color-bg);
  padding: var(--spacing-xl);
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border);
  transition: all var(--transition-base);
}

.feature-card:hover {
  border-color: var(--color-primary-light);
  box-shadow: var(--shadow-lg);
  transform: translateY(-4px);
}

.feature-icon {
  width: 48px;
  height: 48px;
  background: var(--feature-icon-bg);
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 24px;
  margin-bottom: var(--spacing-md);
}

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

.feature-card p {
  color: var(--color-text-light);
  font-size: var(--font-size-sm);
}

/* How It Works Section */
.how-it-works {
  padding: var(--spacing-4xl) 0;
  background: var(--color-bg-alt);
}

.steps {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--spacing-xl);
}

.step {
  text-align: center;
  flex: 1;
  max-width: 280px;
}

.step-number {
  width: 48px;
  height: 48px;
  background: var(--color-primary);
  color: var(--color-text-inverse);
  border-radius: var(--radius-full);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: var(--font-size-xl);
  font-weight: 700;
  margin: 0 auto var(--spacing-md);
}

.step h3 {
  margin-bottom: var(--spacing-sm);
}

.step p {
  color: var(--color-text-light);
  font-size: var(--font-size-sm);
}

.step-arrow {
  font-size: var(--font-size-2xl);
  color: var(--color-text-light);
}

/* FAQ Section */
.faq {
  padding: var(--spacing-4xl) 0;
  background: var(--color-bg-alt);
}

.faq-list {
  max-width: 800px;
  margin: 0 auto;
}

.faq-item {
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  margin-bottom: var(--spacing-md);
  overflow: hidden;
}

.faq-question {
  width: 100%;
  padding: var(--spacing-lg);
  background: none;
  border: none;
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: var(--font-size-base);
  font-weight: 500;
  text-align: left;
  color: var(--color-text);
}

.faq-question:hover {
  background: var(--color-bg-alt);
}

.faq-icon {
  font-size: var(--font-size-xl);
  color: var(--color-primary);
  transition: transform var(--transition-base);
}

.faq-item.open .faq-icon {
  transform: rotate(45deg);
}

.faq-answer {
  max-height: 0;
  overflow: hidden;
  transition: max-height var(--transition-slow);
}

.faq-item.open .faq-answer {
  max-height: 500px;
}

.faq-answer p {
  padding: 0 var(--spacing-lg) var(--spacing-lg);
  color: var(--color-text-light);
}

/* CTA Section */
.cta-section {
  padding: var(--spacing-4xl) 0;
  background: var(--color-primary);
  text-align: center;
}

.cta-section h2 {
  color: var(--color-text-inverse);
  font-size: var(--font-size-3xl);
  margin-bottom: var(--spacing-sm);
}

.cta-section p {
  color: rgba(255, 255, 255, 0.8);
  font-size: var(--font-size-lg);
  margin-bottom: var(--spacing-xl);
}

.cta-section .btn-primary {
  background: var(--color-text-inverse);
  color: var(--color-primary);
}

.cta-section .btn-primary:hover {
  background: var(--color-bg-alt);
}

/* Footer */
.footer {
  background: var(--color-bg-dark);
  color: var(--color-text-inverse);
  padding: var(--spacing-3xl) 0 var(--spacing-xl);
}

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

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

.footer-brand .logo-text {
  color: var(--color-text-inverse);
}

.footer-brand p {
  color: #9ca3af;
}

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

.footer-column h4 {
  font-size: var(--font-size-sm);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: var(--spacing-md);
  color: #9ca3af;
}

.footer-column ul {
  list-style: none;
}

.footer-column li {
  margin-bottom: var(--spacing-sm);
}

.footer-column a {
  color: var(--color-text-inverse);
  text-decoration: none;
  font-size: var(--font-size-sm);
  transition: color var(--transition-fast);
}

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

.footer-bottom {
  border-top: 1px solid #374151;
  padding-top: var(--spacing-xl);
  text-align: center;
}

.footer-bottom .disclaimer {
  font-size: var(--font-size-sm);
  color: #9ca3af;
  margin-bottom: var(--spacing-md);
}

.footer-bottom .copyright {
  font-size: var(--font-size-sm);
  color: #6b7280;
}

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

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

  .hero-visual {
    max-width: 500px;
    margin: 0 auto;
  }

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

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

@media (max-width: 768px) {
  :root {
    --font-size-5xl: 2.25rem;
    --font-size-4xl: 2rem;
    --font-size-3xl: 1.75rem;
  }

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

  .nav-links {
    position: fixed;
    top: var(--nav-height);
    left: 0;
    right: 0;
    background: var(--color-bg);
    flex-direction: column;
    padding: var(--spacing-lg);
    border-bottom: 1px solid var(--color-border);
    gap: var(--spacing-md);
    transform: translateY(-100%);
    opacity: 0;
    visibility: hidden;
    transition: all var(--transition-base);
  }

  .nav-links.open {
    transform: translateY(0);
    opacity: 1;
    visibility: visible;
  }

  .nav-links a {
    padding: var(--spacing-sm) 0;
  }

  .language-selector {
    order: -1;
    width: 100%;
  }

  .lang-btn {
    width: 100%;
    justify-content: center;
  }

  .lang-dropdown {
    position: static;
    margin-top: var(--spacing-sm);
    box-shadow: none;
    border: 1px solid var(--color-border);
  }

  .lang-dropdown.open {
    transform: none;
  }

  .theme-toggle {
    order: -2;
    width: 100%;
    justify-content: center;
  }

  .hero {
    padding-top: calc(var(--nav-height) + var(--spacing-2xl));
    padding-bottom: var(--spacing-2xl);
  }

  .hero-cta {
    flex-direction: column;
  }

  .hero-cta .btn {
    width: 100%;
  }

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

  .steps {
    flex-direction: column;
  }

  .step-arrow {
    transform: rotate(90deg);
  }

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

@media (max-width: 480px) {
  .container {
    padding: 0 var(--spacing-sm);
  }

  .hero-note {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xs);
  }

  .hero-note .separator {
    display: none;
  }
}

/* Fade-in Animations */
.fade-in {
  opacity: 0;
  transform: translateY(20px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.fade-in-visible {
  opacity: 1;
  transform: translateY(0);
}

/* Reduced motion preference */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }

  html {
    scroll-behavior: auto;
  }

  .fade-in {
    opacity: 1;
    transform: none;
  }
}