/**
 * Convert a hex color code to an RGBA color string.
 * @param hex - The hex color code, e.g. "#ff00ff" or "#f0f".
 * @param alpha - The alpha value (optional), default is 1 (fully opaque).
 * @returns The RGBA color string.
 */
export declare function hexToRgba(hex: string, alpha?: number): string;
