/* CSS Custom Properties - Design System */
:root {
  /* Typography Scale */
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-serif: "Georgia", "Times New Roman", serif;
  --font-mono: "SF Mono", "Monaco", "Inconsolata", "Fira Code", monospace;

  /* Font Sizes - Modular Scale (1.250 - Major Third) */
  --text-xs: 0.8rem;
  /* 12.8px */
  --text-sm: 0.875rem;
  /* 14px */
  --text-base: 1rem;
  /* 16px */
  --text-lg: 1.125rem;
  /* 18px */
  --text-xl: 1.25rem;
  /* 20px */
  --text-2xl: 1.563rem;
  /* 25px */
  --text-3xl: 1.953rem;
  /* 31.25px */
  --text-4xl: 2.441rem;
  /* 39px */
  --text-5xl: 3.052rem;
  /* 48.83px */

  /* Spacing Scale */
  --space-1: 0.25rem;
  /* 4px */
  --space-2: 0.5rem;
  /* 8px */
  --space-3: 0.75rem;
  /* 12px */
  --space-4: 1rem;
  /* 16px */
  --space-5: 1.5rem;
  /* 24px */
  --space-6: 2rem;
  /* 32px */
  --space-8: 3rem;
  /* 48px */
  --space-10: 4rem;
  /* 64px */
  --space-12: 6rem;
  /* 96px */

  /* Color Palette - Light Mode */
  --color-text-primary: #1a1a1a;
  --color-text-secondary: #525252;
  --color-text-tertiary: #737373;
  --color-text-muted: #a3a3a3;

  --color-bg-primary: #fafafa;
  --color-bg-secondary: #ffffff;
  --color-bg-tertiary: #f5f5f5;

  --color-border-light: #f0f0f0;
  --color-border-medium: #e5e5e5;
  --color-border-dark: #d4d4d4;

  --color-accent: #667eea;
  --color-accent-hover: #5568d3;
  --color-accent-light: #e0e7ff;

  /* Layout */
  --container-max: 1200px;
  --content-max: 720px;
  --container-padding: 2rem;

  /* Borders & Radius */
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --radius-full: 9999px;

  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-base: 250ms ease;
  --transition-slow: 350ms ease;

  /* 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);
}

/* Dark Mode Color Palette */
[data-theme="dark"] {
  /* Text Colors */
  --color-text-primary: #e5e5e5;
  --color-text-secondary: #a3a3a3;
  --color-text-tertiary: #737373;
  --color-text-muted: #525252;

  /* Background Colors */
  --color-bg-primary: #0a0a0a;
  --color-bg-secondary: #141414;
  --color-bg-tertiary: #1a1a1a;

  /* Border Colors */
  --color-border-light: #1a1a1a;
  --color-border-medium: #262626;
  --color-border-dark: #404040;

  /* Accent Colors */
  --color-accent: #818cf8;
  --color-accent-hover: #a5b4fc;
  --color-accent-light: #1e1b4b;

  /* Shadows - darker and more subtle in dark mode */
  --shadow-sm: 0 1px 2px 0 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, 0.5);
}

/* System Preference - Auto Dark Mode */
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    /* Text Colors */
    --color-text-primary: #e5e5e5;
    --color-text-secondary: #a3a3a3;
    --color-text-tertiary: #737373;
    --color-text-muted: #525252;

    /* Background Colors */
    --color-bg-primary: #0a0a0a;
    --color-bg-secondary: #141414;
    --color-bg-tertiary: #1a1a1a;

    /* Border Colors */
    --color-border-light: #1a1a1a;
    --color-border-medium: #262626;
    --color-border-dark: #404040;

    /* Accent Colors */
    --color-accent: #818cf8;
    --color-accent-hover: #a5b4fc;
    --color-accent-light: #1e1b4b;

    /* Shadows */
    --shadow-sm: 0 1px 2px 0 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, 0.5);
  }
}

/* Reset and Base Styles */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

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

body {
  font-family: var(--font-sans);
  line-height: 1.7;
  color: var(--color-text-primary);
  background: var(--color-bg-primary);
  display: flex;
  flex-direction: column;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  transition: background-color var(--transition-base), color var(--transition-base);
}

/* Smooth theme transitions for all color-dependent elements */
* {
  transition-property: background-color, border-color, color, fill, stroke;
  transition-duration: var(--transition-base);
  transition-timing-function: ease;
}

/* Header */
.site-header {
  background: var(--color-bg-primary);
  border-bottom: 1px solid var(--color-border-medium);
  padding: var(--space-5) 0;
  z-index: 100;
}

.site-header .container {
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 var(--container-padding);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.site-title {
  font-size: var(--text-xl);
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--color-text-primary);
  text-decoration: none;
  transition: color var(--transition-base);
}

.site-title:hover {
  color: var(--color-accent);
}

.site-nav {
  display: flex;
  gap: var(--space-6);
}

.site-nav a {
  color: var(--color-text-secondary);
  text-decoration: none;
  font-weight: 500;
  font-size: var(--text-base);
  transition: color var(--transition-base);
  position: relative;
}

.site-nav a:hover,
.site-nav a.active {
  color: var(--color-text-primary);
}

.site-nav a.active::after {
  content: '';
  position: absolute;
  bottom: -0.5rem;
  left: 0;
  right: 0;
  height: 2px;
  background: var(--color-accent);
}

/* Dark Mode Toggle */
.theme-toggle {
  background: var(--color-bg-tertiary);
  border: 1px solid var(--color-border-medium);
  border-radius: var(--radius-full);
  width: 40px;
  height: 40px;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: background var(--transition-base), border-color var(--transition-base), transform var(--transition-fast);
  margin-left: var(--space-4);
}

.theme-toggle:hover {
  background: var(--color-bg-secondary);
  border-color: var(--color-border-dark);
  transform: scale(1.05);
}

.theme-toggle:active {
  transform: scale(0.95);
}

.theme-toggle svg {
  width: 20px;
  height: 20px;
  color: var(--color-text-secondary);
  transition: color var(--transition-base), transform var(--transition-slow);
}

.theme-toggle:hover svg {
  color: var(--color-text-primary);
}

.theme-toggle .icon-sun,
.theme-toggle .icon-moon {
  position: absolute;
  transition: opacity var(--transition-base), transform var(--transition-base);
}

[data-theme="light"] .theme-toggle .icon-sun {
  opacity: 1;
  transform: rotate(0deg) scale(1);
}

[data-theme="light"] .theme-toggle .icon-moon {
  opacity: 0;
  transform: rotate(180deg) scale(0);
}

[data-theme="dark"] .theme-toggle .icon-sun {
  opacity: 0;
  transform: rotate(-180deg) scale(0);
}

[data-theme="dark"] .theme-toggle .icon-moon {
  opacity: 1;
  transform: rotate(0deg) scale(1);
}

/* If no theme is set and system prefers dark */
@media (prefers-color-scheme: dark) {
  :root:not([data-theme]) .theme-toggle .icon-sun {
    opacity: 0;
    transform: rotate(-180deg) scale(0);
  }

  :root:not([data-theme]) .theme-toggle .icon-moon {
    opacity: 1;
    transform: rotate(0deg) scale(1);
  }
}

/* Main Content */
.site-main {
  flex: 1;
}

/* Footer */
.site-footer {
  background: var(--color-bg-secondary);
  border-top: 1px solid var(--color-border-medium);
  padding: var(--space-8) 0 var(--space-6);
  margin-top: var(--space-10);
  color: var(--color-text-secondary);
}

.site-footer .container {
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 var(--container-padding);
}

.footer-content {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr;
  gap: var(--space-8);
  margin-bottom: var(--space-6);
}

.footer-section h3 {
  font-size: var(--text-xl);
  font-weight: 700;
  margin-bottom: var(--space-3);
  color: var(--color-text-primary);
  letter-spacing: -0.02em;
}

.footer-section h4 {
  font-size: var(--text-sm);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: var(--space-5);
  color: var(--color-text-primary);
}

.footer-section p {
  font-size: var(--text-base);
  line-height: 1.7;
  color: var(--color-text-secondary);
  margin: 0;
}

.footer-nav {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}

.footer-nav a {
  color: var(--color-text-secondary);
  text-decoration: none;
  font-size: var(--text-base);
  transition: color var(--transition-base);
}

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

.social-links {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}

.social-links a {
  color: var(--color-text-secondary);
  text-decoration: none;
  font-size: var(--text-base);
  transition: color var(--transition-base);
}

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

.footer-copyright {
  padding-top: var(--space-6);
  border-top: 1px solid var(--color-border-medium);
  text-align: center;
  font-size: var(--text-sm);
  color: var(--color-text-muted);
  margin: 0;
}

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

/* Responsive */
@media (max-width: 768px) {
  :root {
    --container-padding: 1.5rem;
  }

  .footer-content {
    grid-template-columns: 1fr;
    gap: var(--space-6);
  }

  .site-header .container {
    flex-direction: column;
    gap: var(--space-4);
  }

  .site-nav {
    gap: var(--space-5);
  }

  html {
    font-size: 15px;
  }
}