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

[yaffs-website] / web / core / themes / stable / css / core / dialog / off-canvas.layout.css

/**
 * @file
 * Visual styling for layouts in the off-canvas dialog.
 *
 * See seven/css/layout/layout.css
 */

.layout-icon__region {
  fill: #f5f5f2;
  stroke: #666;
}