> The individual “Show Answer” buttons are doing nothing on mobile Safari.

It should be fixed.

            :host(.hidden), :host(.hidden) * {
                /*
                 * display: none; does not work because of a bug.
                 * bug: https://bugs.webkit.org/show_bug.cgi?id=188259
                 */
                visibility: hidden;
                width: 0;
                height: 0;
            }