    cssEl = document.createElement("style");
                    cssEl.innerHTML = css;
                    document.body.appendChild(cssEl)
                    this.backdropOverride = cssEl
                } else {
                    var completed;
                    this.addEventListener("core-overlay-close-completed", completed = function() {
                        this.removeEventListener("core-overlay-close-completed", completed);
                        if(this.backdropOverride) this.backdropOverri