Updated Drupal to 8.6. This goes with the following updates because it's possible...

[yaffs-website] / web / core / misc / normalize-fixes.css

/**
 * @file
 * Fixes for core/assets/vendor/normalize-css/normalize.css since version 3.
 */

/**
 * Fix problem with details/summary lines missing the drop arrows.
 */
@media (min--moz-device-pixel-ratio: 0) {
  summary {
    display: list-item;
  }
}