import type { Unregister } from "../types.js";
/**
 * Calls `callback` with a boolean value indicating whether the user has requested the dark theme.
 * If calls it immediately with the current state of the dark theme, and everytime it changes, until the returned function is called.
 *
 * @param callback The `callback` called with the boolean value indicating whether the user has requested the dark theme.
 * @returns A function that stops listening for theme changes.
 */
export declare function onDark(callback: (dark: boolean) => void): Unregister | undefined;