/**
 * Extract CSS rules from a style element's CSSOM (CSSStyleSheet).
 * Returns the concatenated cssText of all rules, or null if unavailable.
 *
 * CSS-in-JS libraries (React Native Web, styled-components, etc.) inject
 * styles via insertRule() — their <style> elements have empty textContent
 * but rules exist in the CSSOM. This helper extracts those rules.
 */
export declare function extractCssomRules(style: HTMLStyleElement): string | null;