/**
 * Detects whether the viewport matches a mobile breakpoint.
 *
 * @param breakpoint - Max-width in pixels to consider as mobile. Defaults to 768.
 * @returns A boolean indicating whether the viewport is at or below the breakpoint.
 *
 * @example
 * ```tsx
 * const Component = () => {
 *     const isMobile = useIsMobile();
 *     return <div>{isMobile ? 'Mobile' : 'Desktop'}</div>;
 * };
 *
 * // Custom breakpoint
 * const isTablet = useIsMobile(1024);
 * ```
 */
export declare function useIsMobile(breakpoint?: number): boolean;