:root {
  /* Default Light Theme - Neutral warm canvas */
  --bg-primary: #FAF9F6;
  --bg-surface: #FFFFFF;
  --bg-surface-subtle: #F3EFEA;
  --bg-elevated: rgba(255, 255, 255, 0.92);
  
  --text-primary: #121214;
  --text-secondary: #585860;
  --text-muted: #8E8E98;
  --text-inverse: #FAF9F6;

  /* 3-Color Educational Palette */
  /* 1. Deep Blue: Knowledge, mathematics, trust, primary interactive */
  --accent-blue: #2563EB;
  --accent-blue-subtle: rgba(37, 99, 235, 0.08);
  --accent-blue-glow: rgba(37, 99, 235, 0.25);
  --border-blue: rgba(37, 99, 235, 0.3);

  /* 2. Soft Teal: Discovery, exploration, interaction, hover states, transformations */
  --accent-teal: #14B8A6;
  --accent-teal-subtle: rgba(20, 184, 166, 0.08);
  --accent-teal-glow: rgba(20, 184, 166, 0.25);
  --border-teal: rgba(20, 184, 166, 0.3);

  /* 3. Warm Yellow: Curiosity, ideas, moments of discovery, highlighted values */
  --accent-yellow: #F5C542;
  --accent-yellow-subtle: rgba(245, 197, 66, 0.12);
  --accent-yellow-glow: rgba(245, 197, 66, 0.3);
  --border-yellow: rgba(245, 197, 66, 0.35);

  /* Functional Aliases & Backwards Compatibility */
  --accent-primary: var(--accent-blue);
  --accent-secondary: var(--accent-teal);
  --accent-highlight: var(--accent-yellow);
  --accent-purple: var(--accent-blue);
  --accent-purple-light: var(--accent-teal);
  --accent-purple-dark: #1D4ED8;
  --accent-purple-subtle: var(--accent-blue-subtle);
  --accent-purple-glow: var(--accent-blue-glow);
  --border-purple: var(--border-blue);

  /* Mathematical Lines & Borders */
  --border-subtle: rgba(18, 18, 20, 0.08);
  --border-strong: rgba(18, 18, 20, 0.18);
  --grid-line: rgba(18, 18, 20, 0.04);

  /* Typography */
  --font-main: 'Plus Jakarta Sans', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
  --font-mono: 'JetBrains Mono', 'SF Mono', Consolas, Monaco, monospace;
  --font-serif: 'Instrument Serif', Georgia, serif;

  /* Shadows */
  --shadow-sm: 0 2px 8px rgba(18, 18, 20, 0.04);
  --shadow-md: 0 8px 24px rgba(18, 18, 20, 0.06);
  --shadow-lg: 0 16px 40px rgba(18, 18, 20, 0.08);
  --shadow-glass: 0 8px 32px 0 rgba(37, 99, 235, 0.06);

  /* Transitions */
  --transition-smooth: cubic-bezier(0.16, 1, 0.3, 1);
  --transition-bounce: cubic-bezier(0.34, 1.56, 0.64, 1);
  --theme-transition: background-color 0.45s ease, color 0.45s ease, border-color 0.45s ease, box-shadow 0.45s ease;

  /* Spacing & Layout */
  --container-max-width: 1440px;
  --container-padding: clamp(1.25rem, 5vw, 4rem);
  --section-padding-y: clamp(5rem, 12vh, 10rem);
}

/* ==================================================
   DARK MODE PALETTE
   - Deep near-black / charcoal background
   - Soft white typography
   - Selective Blue, Teal, and Yellow accents
   ================================================== */
[data-theme="dark"] {
  --bg-primary: #0C0C0E;
  --bg-surface: #141418;
  --bg-surface-subtle: #1C1C22;
  --bg-elevated: rgba(20, 20, 24, 0.92);
  
  --text-primary: #F7F5F2;
  --text-secondary: #A0A0AA;
  --text-muted: #6E6E7C;
  --text-inverse: #0C0C0E;

  --accent-blue: #3B82F6;
  --accent-blue-subtle: rgba(59, 130, 246, 0.15);
  --accent-blue-glow: rgba(59, 130, 246, 0.35);
  --border-blue: rgba(59, 130, 246, 0.35);

  --accent-teal: #14B8A6;
  --accent-teal-subtle: rgba(20, 184, 166, 0.15);
  --accent-teal-glow: rgba(20, 184, 166, 0.35);
  --border-teal: rgba(20, 184, 166, 0.35);

  --accent-yellow: #F5C542;
  --accent-yellow-subtle: rgba(245, 197, 66, 0.18);
  --accent-yellow-glow: rgba(245, 197, 66, 0.4);
  --border-yellow: rgba(245, 197, 66, 0.4);

  --border-subtle: rgba(255, 255, 255, 0.08);
  --border-strong: rgba(255, 255, 255, 0.18);
  --grid-line: rgba(255, 255, 255, 0.03);

  --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 8px 24px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 16px 40px rgba(0, 0, 0, 0.5);
  --shadow-glass: 0 8px 32px 0 rgba(59, 130, 246, 0.12);
}