:root {
  /* Colors - Dark Theme (Default) */
  --color-bg-primary: #0f172a;
  --color-bg-secondary: #1e293b;
  --color-bg-tertiary: #334155;
  --color-surface: rgba(30, 41, 59, 0.7);
  --color-surface-glass: rgba(30, 41, 59, 0.5);
  
  --color-text-primary: #f8fafc;
  --color-text-secondary: #94a3b8;
  --color-text-tertiary: #64748b;
  
  --color-accent: #3b82f6;
  --color-accent-hover: #2563eb;
  --color-accent-light: rgba(59, 130, 246, 0.1);
  --color-accent-glow: rgba(59, 130, 246, 0.3);
  
  --color-success: #10b981;
  --color-warning: #f59e0b;
  --color-error: #ef4444;
  
  --color-border: rgba(148, 163, 184, 0.1);
  --color-border-hover: rgba(148, 163, 184, 0.2);
  
  /* Typography */
  --font-family: 'Inter', system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-size-xs: clamp(0.75rem, 0.7rem + 0.25vw, 0.875rem);
  --font-size-sm: clamp(0.875rem, 0.8rem + 0.375vw, 1rem);
  --font-size-base: clamp(1rem, 0.9rem + 0.5vw, 1.125rem);
  --font-size-lg: clamp(1.125rem, 1rem + 0.625vw, 1.25rem);
  --font-size-xl: clamp(1.25rem, 1.1rem + 0.75vw, 1.5rem);
  --font-size-2xl: clamp(1.5rem, 1.25rem + 1.25vw, 2rem);
  --font-size-3xl: clamp(2rem, 1.5rem + 2.5vw, 3rem);
  --font-size-4xl: clamp(2.5rem, 2rem + 2.5vw, 4rem);
  
  --line-height-tight: 1.25;
  --line-height-base: 1.6;
  --line-height-relaxed: 1.75;
  
  /* Spacing */
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.25rem;
  --space-6: 1.5rem;
  --space-8: 2rem;
  --space-10: 2.5rem;
  --space-12: 3rem;
  --space-16: 4rem;
  --space-20: 5rem;
  --space-24: 6rem;
  --space-32: 8rem;
  
  /* Layout */
  --container-max: 1200px;
  --container-narrow: 800px;
  --header-height: 80px;
  
  /* Borders */
  --radius-sm: 0.375rem;
  --radius-md: 0.5rem;
  --radius-lg: 0.75rem;
  --radius-xl: 1rem;
  --radius-2xl: 1.5rem;
  --radius-full: 9999px;
  
  /* Shadows */
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.3), 0 2px 4px -2px rgba(0, 0, 0, 0.3);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.3), 0 4px 6px -4px rgba(0, 0, 0, 0.3);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.3), 0 8px 10px -6px rgba(0, 0, 0, 0.3);
  --shadow-2xl: 0 25px 50px -12px rgba(0, 0, 0, 0.5);
  --shadow-glow: 0 0 40px rgba(59, 130, 246, 0.15);
  
  /* Transitions */
  --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-base: 250ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: 350ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-bounce: 500ms cubic-bezier(0.34, 1.56, 0.64, 1);
  
  /* Z-index layers */
  --z-base: 1;
  --z-dropdown: 100;
  --z-sticky: 200;
  --z-modal: 300;
  --z-toast: 400;
  --z-tooltip: 500;
}

/* Light Theme */
[data-theme="light"] {
  --color-bg-primary: #ffffff;
  --color-bg-secondary: #f8fafc;
  --color-bg-tertiary: #f1f5f9;
  --color-surface: rgba(255, 255, 255, 0.8);
  --color-surface-glass: rgba(255, 255, 255, 0.7);
  
  --color-text-primary: #0f172a;
  --color-text-secondary: #475569;
  --color-text-tertiary: #94a3b8;
  
  --color-border: rgba(15, 23, 42, 0.08);
  --color-border-hover: rgba(15, 23, 42, 0.15);
  
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -2px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -4px rgba(0, 0, 0, 0.1);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 8px 10px -6px rgba(0, 0, 0, 0.1);
  --shadow-2xl: 0 25px 50px -12px rgba(0, 0, 0, 0.15);
}

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

html {
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

body {
  font-family: var(--font-family);
  font-size: var(--font-size-base);
  line-height: var(--line-height-base);
  color: var(--color-text-primary);
  background-color: var(--color-bg-primary);
  background-image: 
    radial-gradient(ellipse at top, rgba(59, 130, 246, 0.08) 0%, transparent 50%),
    radial-gradient(ellipse at bottom right, rgba(59, 130, 246, 0.05) 0%, transparent 40%);
  background-attachment: fixed;
  min-height: 100vh;
  overflow-x: hidden;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  font-weight: 600;
  line-height: var(--line-height-tight);
  letter-spacing: -0.02em;
}

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); }
h5 { font-size: var(--font-size-lg); }
h6 { font-size: var(--font-size-base); }

p {
  margin-bottom: var(--space-4);
  color: var(--color-text-secondary);
}

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

a:hover {
  color: var(--color-accent-hover);
}

/* Container */
.container {
  width: 100%;
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 var(--space-6);
}

.container-narrow {
  max-width: var(--container-narrow);
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  padding: var(--space-3) var(--space-6);
  font-family: var(--font-family);
  font-size: var(--font-size-sm);
  font-weight: 500;
  line-height: 1;
  text-decoration: none;
  border: 1px solid transparent;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-base);
  white-space: nowrap;
}

.btn-primary {
  background: linear-gradient(135deg, var(--color-accent) 0%, var(--color-accent-hover) 100%);
  color: white;
  box-shadow: 0 4px 14px rgba(59, 130, 246, 0.4);
}

.btn-primary:hover {
  transform: translateY(-1px);
  box-shadow: 0 6px 20px rgba(59, 130, 246, 0.5);
  color: white;
}

.btn-secondary {
  background: var(--color-surface);
  color: var(--color-text-primary);
  border-color: var(--color-border);
  backdrop-filter: blur(8px);
}

.btn-secondary:hover {
  background: var(--color-bg-tertiary);
  border-color: var(--color-border-hover);
  color: var(--color-text-primary);
}

.btn-ghost {
  background: transparent;
  color: var(--color-text-secondary);
}

.btn-ghost:hover {
  background: var(--color-accent-light);
  color: var(--color-accent);
}

.btn-lg {
  padding: var(--space-4) var(--space-8);
  font-size: var(--font-size-base);
}

.btn-sm {
  padding: var(--space-2) var(--space-4);
  font-size: var(--font-size-xs);
}

/* Cards */
.card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xl);
  padding: var(--space-6);
  backdrop-filter: blur(12px);
  transition: all var(--transition-base);
}

.card:hover {
  border-color: var(--color-border-hover);
  box-shadow: var(--shadow-glow);
}

/* Forms */
.form-group {
  margin-bottom: var(--space-5);
}

.form-label {
  display: block;
  margin-bottom: var(--space-2);
  font-size: var(--font-size-sm);
  font-weight: 500;
  color: var(--color-text-primary);
}

.form-input,
.form-textarea,
.form-select {
  width: 100%;
  padding: var(--space-3) var(--space-4);
  font-family: var(--font-family);
  font-size: var(--font-size-base);
  color: var(--color-text-primary);
  background: var(--color-bg-secondary);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  transition: all var(--transition-fast);
}

.form-input:focus,
.form-textarea:focus,
.form-select:focus {
  outline: none;
  border-color: var(--color-accent);
  box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
}

.form-input::placeholder,
.form-textarea::placeholder {
  color: var(--color-text-tertiary);
}

.form-textarea {
  min-height: 120px;
  resize: vertical;
}

.form-checkbox-group {
  display: flex;
  align-items: flex-start;
  gap: var(--space-3);
}

.form-checkbox {
  width: 18px;
  height: 18px;
  margin-top: 2px;
  accent-color: var(--color-accent);
  cursor: pointer;
}

.form-checkbox-label {
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
  line-height: var(--line-height-base);
}

.form-error {
  color: var(--color-error);
  font-size: var(--font-size-sm);
  margin-top: var(--space-1);
}

.form-input.error,
.form-textarea.error {
  border-color: var(--color-error);
}

/* Sections */
.section {
  padding: var(--space-20) 0;
}

.section-header {
  text-align: center;
  max-width: var(--container-narrow);
  margin: 0 auto var(--space-12);
}

.section-title {
  margin-bottom: var(--space-4);
}

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

/* Grid */
.grid {
  display: grid;
  gap: var(--space-6);
}

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

@media (max-width: 1024px) {
  .grid-4 { grid-template-columns: repeat(2, 1fr); }
  .grid-3 { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 768px) {
  .grid-2, .grid-3, .grid-4 { grid-template-columns: 1fr; }
}

/* Utilities */
.text-center { text-align: center; }
.text-accent { color: var(--color-accent); }
.text-success { color: var(--color-success); }
.text-error { color: var(--color-error); }

.mb-4 { margin-bottom: var(--space-4); }
.mb-6 { margin-bottom: var(--space-6); }
.mb-8 { margin-bottom: var(--space-8); }
.mb-12 { margin-bottom: var(--space-12); }

.mt-4 { margin-top: var(--space-4); }
.mt-6 { margin-top: var(--space-6); }
.mt-8 { margin-top: var(--space-8); }

.flex { display: flex; }
.flex-col { flex-direction: column; }
.items-center { align-items: center; }
.justify-center { justify-content: center; }
.justify-between { justify-content: space-between; }
.gap-4 { gap: var(--space-4); }
.gap-6 { gap: var(--space-6); }

/* Focus visible */
:focus-visible {
  outline: 2px solid var(--color-accent);
  outline-offset: 2px;
}

/* Selection */
::selection {
  background: var(--color-accent);
  color: white;
}

/* Scrollbar */
::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}

::-webkit-scrollbar-track {
  background: var(--color-bg-secondary);
}

::-webkit-scrollbar-thumb {
  background: var(--color-bg-tertiary);
  border-radius: var(--radius-full);
}

::-webkit-scrollbar-thumb:hover {
  background: var(--color-text-tertiary);
}