/**
 * Queries up the DOM for given `selector`, starting from given `leafElement`.
 * The first element found matching `selector` will be returned.
 * Querying will stop as soon as given `root` is encountered.
 * If no matching element was found, `null` is returned.
 *
 * Based on the {@link https://developer.mozilla.org/en-US/docs/Web/API/Element/closest#Polyfill MDN `closest` polyfill}
 *
 * @param leaf     The innermost element in the DOM tree to start searching from.
 * @param selector The selector (CSS style) to match ancestor elements with.
 * @param root     The element that acts as a scope for the query.
 */
export declare function closestWithin(leaf: HTMLElement, selector: string, root: Node): HTMLElement | null;