:root {
  /* --- Brand Colors (Modern Indigo) --- */
  --primary-50: #eef2ff;
  --primary-100: #e0e7ff;
  --primary-200: #c7d2fe;
  --primary-500: #6366f1;
  --primary-600: #4f46e5;
  --primary-700: #4338ca;

  --accent-color: var(--primary-600);
  --accent-gradient: linear-gradient(135deg, var(--primary-600), var(--primary-700));

  --secondary-50: #ecfdf5;
  --secondary-500: #10b981;
  --secondary-600: #059669;

  /* --- Neutral Colors (Slate) --- */
  --bg-page: #f8fafc;
  --bg-card: #ffffff;
  --bg-overlay: rgba(15, 23, 42, 0.4);

  --text-primary: #1e293b;
  --text-secondary: #64748b;
  --text-inverse: #ffffff;

  --border-light: #e2e8f0;
  --border-focus: #a5b4fc;

  /* --- Functional Colors --- */
  --color-error: #ef4444;
  --color-warning: #f59e0b;
  --color-success: #10b981;

  /* --- Legacy Variables Mapped --- */
  --primary-color: var(--primary-600);
  --secondary-color: var(--color-error);
  --background-color: var(--bg-page);
  --card-background-color: var(--bg-card);
  --text-color: var(--text-primary);
  --text-color-light: var(--text-secondary);
  --border-color: var(--border-light);
  --success-color: var(--color-success);
  --success-bg: var(--secondary-50);
  --google-red: var(--color-error);

  /* --- Typography --- */
  --font-primary: 'Inter', system-ui, -apple-system, sans-serif;
  --font-size-base: 15px;

  /* --- Spacing & Layout (8pt Grid) --- */
  --space-1: 4px;
  --space-2: 8px;
  --space-3: 12px;
  --space-4: 16px;
  --space-6: 24px;
  --space-8: 32px;

  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 20px;
  --radius-full: 9999px;

  /* --- Shadows (Premium Soft Layers) --- */
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.07), 0 2px 4px -1px rgba(0, 0, 0, 0.04);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.08), 0 4px 6px -2px rgba(0, 0, 0, 0.03);
  --shadow-premium: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);

  /* --- Animation --- */
  --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-base: 300ms cubic-bezier(0.4, 0, 0.2, 1);

  /* --- Card Identity Colors --- */
  --card-flashcards: #8b5cf6;
  --card-google-form: #10b981;
  --card-video: #f43f5e;
  --card-lesson: #3b82f6;
  --card-quiz: #f59e0b;

  /* --- Mobile App Specifics --- */
  --header-height-mobile: 56px;
  --footer-height-mobile: 48px;
  --radius-app: 24px;
}

/* Global Box Sizing Reset */
*,
*::before,
*::after {
  box-sizing: border-box;
}