/* ============================================
   Base Styles & CSS Variables
   ============================================ */

:root {
  /* Colors - Light Theme */
  --color-bg-primary: #ffffff;
  --color-bg-secondary: #f8f9fa;
  --color-bg-tertiary: #e9ecef;
  --color-text-primary: #212529;
  --color-text-secondary: #6c757d;
  --color-text-muted: #adb5bd;
  --color-accent: #0d6efd;
  --color-accent-hover: #0b5ed7;
  --color-border: #dee2e6;
  --color-shadow: rgba(0, 0, 0, 0.1);
  --color-shadow-hover: rgba(0, 0, 0, 0.15);
  
  /* Colors - Dark Theme */
  --color-bg-primary-dark: #1a1a1a;
  --color-bg-secondary-dark: #2d2d2d;
  --color-bg-tertiary-dark: #3d3d3d;
  --color-text-primary-dark: #e9ecef;
  --color-text-secondary-dark: #adb5bd;
  --color-text-muted-dark: #6c757d;
  --color-accent-dark: #4dabf7;
  --color-accent-hover-dark: #339af0;
  --color-border-dark: #404040;
  --color-shadow-dark: rgba(0, 0, 0, 0.3);
  --color-shadow-hover-dark: rgba(0, 0, 0, 0.4);
  
  /* Typography */
  --font-family-base: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen', 'Ubuntu', 'Cantarell', 'Fira Sans', 'Droid Sans', 'Helvetica Neue', sans-serif;
  --font-family-mono: 'SF Mono', 'Monaco', 'Inconsolata', 'Fira Code', 'Fira Mono', 'Droid Sans Mono', 'Source Code Pro', monospace;
  
  --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: 2rem;
  --font-size-4xl: 2.5rem;
  
  --font-weight-normal: 400;
  --font-weight-medium: 500;
  --font-weight-semibold: 600;
  --font-weight-bold: 700;
  
  --line-height-tight: 1.25;
  --line-height-normal: 1.5;
  --line-height-relaxed: 1.75;
  
  /* 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;
  
  /* Layout */
  --container-max-width: 1200px;
  --container-padding: var(--spacing-lg);
  --border-radius: 0.5rem;
  --border-radius-lg: 1rem;
  
  /* Transitions */
  --transition-fast: 500ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-base: 800ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: 1200ms cubic-bezier(0.4, 0, 0.2, 1);
  
  /* Z-index layers */
  --z-dropdown: 1000;
  --z-sticky: 1020;
  --z-fixed: 1030;
  --z-modal-backdrop: 1040;
  --z-modal: 1050;
}

/* Dark theme */
[data-theme="dark"] {
  --color-bg-primary: var(--color-bg-primary-dark);
  --color-bg-secondary: var(--color-bg-secondary-dark);
  --color-bg-tertiary: var(--color-bg-tertiary-dark);
  --color-text-primary: var(--color-text-primary-dark);
  --color-text-secondary: var(--color-text-secondary-dark);
  --color-text-muted: var(--color-text-muted-dark);
  --color-accent: var(--color-accent-dark);
  --color-accent-hover: var(--color-accent-hover-dark);
  --color-border: var(--color-border-dark);
  --color-shadow: var(--color-shadow-dark);
  --color-shadow-hover: var(--color-shadow-hover-dark);
}

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

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: var(--font-family-base);
  font-size: var(--font-size-base);
  line-height: var(--line-height-normal);
  color: var(--color-text-primary);
  background-color: var(--color-bg-primary);
  transition: background-color var(--transition-base), color var(--transition-base);
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  font-weight: var(--font-weight-bold);
  line-height: var(--line-height-tight);
  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); }
h5 { font-size: var(--font-size-lg); }
h6 { font-size: var(--font-size-base); }

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

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

a:hover,
a:focus {
  color: var(--color-accent-hover);
  text-decoration: underline;
}

a:focus-visible {
  outline: 2px solid var(--color-accent);
  outline-offset: 2px;
  border-radius: 2px;
}

/* Lists */
ul, ol {
  margin-bottom: var(--spacing-md);
  padding-left: var(--spacing-xl);
}

li {
  margin-bottom: var(--spacing-xs);
  color: var(--color-text-secondary);
}

/* Code */
code {
  font-family: var(--font-family-mono);
  font-size: 0.9em;
  background-color: var(--color-bg-tertiary);
  padding: 0.125rem 0.375rem;
  border-radius: 0.25rem;
  color: var(--color-text-primary);
}

pre {
  font-family: var(--font-family-mono);
  font-size: var(--font-size-sm);
  background-color: var(--color-bg-tertiary);
  padding: var(--spacing-md);
  border-radius: var(--border-radius);
  overflow-x: auto;
  margin-bottom: var(--spacing-md);
}

pre code {
  background: none;
  padding: 0;
}

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

/* Buttons */
button {
  font-family: inherit;
  font-size: inherit;
  cursor: pointer;
  border: none;
  background: none;
  padding: 0;
}

/* Form Elements */
input,
textarea,
select {
  font-family: inherit;
  font-size: inherit;
  line-height: inherit;
}

/* Accessibility */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border-width: 0;
}

/* Skip to main content link */
.skip-link {
  position: absolute;
  top: -40px;
  left: 0;
  background: var(--color-accent);
  color: white;
  padding: var(--spacing-sm) var(--spacing-md);
  z-index: var(--z-modal);
  text-decoration: none;
}

.skip-link:focus {
  top: 0;
}