/* ===========================
   CSS Reset & Base Styles
   =========================== */

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

/* ===========================
   Design Tokens
   =========================== */

:root {
  /* Colors - Light Mode */
  --color-bg-primary: #FFFFFF;
  --color-bg-secondary: #F9FAFB;
  --color-bg-tertiary: #F3F4F6;

  --color-primary: #3B82F6;
  --color-primary-hover: #2563EB;
  --color-primary-light: #DBEAFE;

  --color-text-primary: #1F2937;
  --color-text-secondary: #6B7280;
  --color-text-tertiary: #9CA3AF;

  --color-success: #10B981;
  --color-success-light: #D1FAE5;
  --color-error: #EF4444;
  --color-error-light: #FEE2E2;

  --color-border: #E5E7EB;
  --color-border-focus: #3B82F6;

  /* Typography */
  --font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;

  --font-size-xs: 12px;
  --font-size-sm: 14px;
  --font-size-base: 16px;
  --font-size-lg: 18px;
  --font-size-xl: 20px;
  --font-size-2xl: 24px;
  --font-size-3xl: 32px;
  --font-size-4xl: 40px;

  --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 */
  --space-1: 4px;
  --space-2: 8px;
  --space-3: 12px;
  --space-4: 16px;
  --space-5: 20px;
  --space-6: 24px;
  --space-8: 32px;
  --space-10: 40px;
  --space-12: 48px;
  --space-16: 64px;
  --space-20: 80px;

  /* Border Radius */
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --radius-xl: 16px;
  --radius-full: 9999px;

  /* 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), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);

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

  /* Layout */
  --container-max-width: 1200px;
  --container-padding: var(--space-6);
}

/* Dark Mode */
[data-theme="dark"] {
  /* Colors - Dark Mode */
  --color-bg-primary: #111827;
  --color-bg-secondary: #1F2937;
  --color-bg-tertiary: #374151;

  --color-primary: #60A5FA;
  --color-primary-hover: #3B82F6;
  --color-primary-light: #1E3A8A;

  --color-text-primary: #F9FAFB;
  --color-text-secondary: #D1D5DB;
  --color-text-tertiary: #9CA3AF;

  --color-success: #34D399;
  --color-success-light: #064E3B;
  --color-error: #F87171;
  --color-error-light: #7F1D1D;

  --color-border: #374151;
  --color-border-focus: #60A5FA;
}

/* ===========================
   Base Elements
   =========================== */

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

body {
  font-family: var(--font-family);
  font-size: var(--font-size-base);
  line-height: var(--line-height-normal);
  color: var(--color-text-primary);
  background-color: var(--color-bg-primary);
  min-height: 100vh;
  transition: background-color 0.3s ease, color 0.3s ease;
}

h1, h2, h3, h4, h5, h6 {
  font-weight: var(--font-weight-bold);
  line-height: var(--line-height-tight);
  color: var(--color-text-primary);
}

h1 {
  font-size: var(--font-size-4xl);
  margin-bottom: var(--space-6);
}

h2 {
  font-size: var(--font-size-3xl);
  margin-bottom: var(--space-5);
}

h3 {
  font-size: var(--font-size-2xl);
  margin-bottom: var(--space-4);
}

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

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

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

/* ===========================
   Layout Utilities
   =========================== */

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

.section {
  padding: var(--space-16) 0;
}

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

.flex {
  display: flex;
}

.flex-col {
  flex-direction: column;
}

.items-center {
  align-items: center;
}

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

.gap-4 {
  gap: var(--space-4);
}

.gap-6 {
  gap: var(--space-6);
}

.gap-8 {
  gap: var(--space-8);
}

/* ===========================
   Button Styles
   =========================== */

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: var(--space-3) var(--space-6);
  font-size: var(--font-size-base);
  font-weight: var(--font-weight-medium);
  line-height: 1;
  border-radius: var(--radius-md);
  border: none;
  cursor: pointer;
  transition: all var(--transition-base);
  text-decoration: none;
  white-space: nowrap;
}

.btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

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

.btn-primary:hover:not(:disabled) {
  background-color: var(--color-primary-hover);
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
}

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

.btn-secondary:hover:not(:disabled) {
  background-color: var(--color-border);
}

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

/* ===========================
   Card Styles
   =========================== */

.card {
  background-color: var(--color-bg-primary);
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border);
  padding: var(--space-6);
  transition: all var(--transition-base);
}

.card:hover {
  box-shadow: var(--shadow-lg);
  transform: translateY(-2px);
}

/* ===========================
   Alert Styles
   =========================== */

.alert {
  padding: var(--space-4);
  border-radius: var(--radius-md);
  font-size: var(--font-size-sm);
  margin-bottom: var(--space-4);
}

.alert-success {
  background-color: var(--color-success-light);
  color: #065F46;
  border: 1px solid var(--color-success);
}

[data-theme="dark"] .alert-success {
  color: #6EE7B7;
}

.alert-error {
  background-color: var(--color-error-light);
  color: #991B1B;
  border: 1px solid var(--color-error);
}

[data-theme="dark"] .alert-error {
  color: #FCA5A5;
}

/* ===========================
   Responsive Breakpoints
   =========================== */

@media (max-width: 768px) {
  :root {
    --font-size-3xl: 28px;
    --font-size-4xl: 32px;
    --container-padding: var(--space-4);
  }

  .section {
    padding: var(--space-12) 0;
  }

  h1 {
    margin-bottom: var(--space-4);
  }
}

@media (max-width: 480px) {
  :root {
    --font-size-3xl: 24px;
    --font-size-4xl: 28px;
  }
}