Gutenberg: Reverse columns for responsive layout

CSS class: right-left:

// max-width depends on the theme, check e.g. with Chrome dev tools
@media (max-width: 768px) { 
  .entry-content .right-left .wp-block-column:nth-child(2) {
    order:1;
  }
  .entry-content .right-left .wp-block-column:first-child {
    order:99;
  }
}

Add it to the columns block: