/**
 * Read a CSS custom property value from :root.
 * Use this inside ECharts options / canvas drawing so colors track CSS variables
 * (e.g. --color-text-secondary) instead of being hard-coded.
 *
 * Stage 3 will add re-render-on-theme-change via a `key={theme}` on chart hosts.
 *
 * @example c('text-secondary')          // → '#8b8ea8' under dark theme
 * @example c('chart-area-from')         // → 'rgba(108, 99, 255, 0.25)' under dark
 */
export function c(token: string): string {
  if (typeof window === 'undefined') return '';
  return getComputedStyle(document.documentElement)
    .getPropertyValue('--color-' + token)
    .trim();
}