/* ============================================
   Andrew Ng ML Course — Design System Foundation
   Adapted from Frame Innovation study guide
   ============================================ */

:root {
  /* Brand Colors */
  --color-primary:   #1e40af;
  --color-secondary: #0d9488;
  --color-accent:    #f59e0b;
  --color-success:   #10b981;
  --color-rose:      #f43f5e;
  --color-indigo:    #6366f1;
  --color-purple:    #8b5cf6;

  /* Grays */
  --gray-50:  #f9fafb;
  --gray-100: #f3f4f6;
  --gray-200: #e5e7eb;
  --gray-300: #d1d5db;
  --gray-400: #9ca3af;
  --gray-500: #6b7280;
  --gray-600: #4b5563;
  --gray-700: #374151;
  --gray-800: #1f2937;
  --gray-900: #111827;

  /* Spacing */
  --space-xs: 4px;
  --space-sm: 8px;
  --space-md: 12px;
  --space-lg: 16px;
  --space-xl: 24px;
  --space-2xl: 32px;
  --space-3xl: 48px;

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

  /* Shadows */
  --shadow-sm:  0 1px 2px rgba(0,0,0,0.05);
  --shadow-md:  0 4px 6px rgba(0,0,0,0.07), 0 2px 4px rgba(0,0,0,0.05);
  --shadow-lg:  0 10px 15px rgba(0,0,0,0.08), 0 4px 6px rgba(0,0,0,0.04);
  --shadow-xl:  0 20px 25px rgba(0,0,0,0.10), 0 8px 10px rgba(0,0,0,0.04);

  /* Transitions */
  --transition-fast: 0.15s ease;
  --transition-normal: 0.25s ease;

  /* Typography */
  --font-heading: Georgia, 'PT Serif', serif;
  --font-body: system-ui, -apple-system, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
  --font-code: 'SF Mono', SFMono-Regular, ui-monospace, 'Cascadia Code', Menlo, monospace;

  --text-xs: 0.75rem;
  --text-sm: 0.875rem;
  --text-base: 1rem;
  --text-lg: 1.125rem;
  --text-xl: 1.25rem;
  --text-2xl: 1.5rem;
  --text-3xl: 2rem;
  --text-4xl: 2.5rem;
}

/* ── Reset ─────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: var(--font-body);
  font-size: var(--text-base);
  line-height: 1.6;
  color: var(--gray-900);
  background-color: var(--gray-50);
  -webkit-font-smoothing: antialiased;
}
img { display: block; max-width: 100%; }
input, button, textarea, select { font: inherit; }
a { color: var(--color-primary); text-decoration: none; transition: color var(--transition-fast); }
a:hover { text-decoration: underline; }

/* ── Typography ────────────────────────────── */
h1, h2, h3, h4 { font-family: var(--font-heading); font-weight: 700; line-height: 1.25; color: var(--gray-900); }
h1 { font-size: var(--text-4xl); letter-spacing: -0.025em; margin-bottom: var(--space-xl); }
h2 { font-size: var(--text-3xl); letter-spacing: -0.02em; margin-bottom: var(--space-lg); }
h3 { font-size: var(--text-2xl); margin-bottom: var(--space-md); }
p { margin-bottom: var(--space-lg); }

/* ── Animations ────────────────────────────── */
@keyframes fadeIn {
  from { opacity: 0; }
  to   { opacity: 1; }
}

@keyframes slideIn {
  from { opacity: 0; transform: translateY(20px); }
  to   { opacity: 1; transform: translateY(0); }
}