this.onEscapeKey = e => {
                if (e.keyCode === 27) {
                    cancel(e);
                } else if (e.keyCode == 13) {
                    ok(e);
                }
            };
            document.addEventListener('keydown', this.onEscapeKey);
        }
        disconnectedCallback() {
            document.removeEventListener('keydown', this.onEscapeKey);
        }
        get heading() {
            return this.getAttribute("heading");
        }
        set heading(value) {
     