/**
 * Decodes a Base64 encoded string to its original form.
 * This is a polyfill for the atob function, which may not be available in all environments.
 *
 * @param {string} input - The Base64 encoded string to decode
 * @returns {string | undefined} The decoded string, or undefined if the input is invalid
 */
export declare const atob: (input: string) => string | undefined;