/**
 * Observes the pixels measure of the cascading `em` unit.
 */
export declare class EMObserver {
    /**
     * Cascading style class.
     */
    static CLASS: string;
    private element;
    private resize_observer;
    /**
     * Constructor.
     */
    constructor(container: HTMLElement, updateFn: (value: number) => void);
    /**
     * Cleanup
     */
    cleanup(): void;
    private read;
}