Style Layout Builder

Taken from: https://www.drupal.org/project/layout_paragraphs/issues/3249337#comment-...

In your sub-theme edit your
barrio_subtheme.layouts.yml

To each of your layouts add the following:
library: barrio_subtheme/advanced-layout-library

Within your barrio_subtheme.libraries.yml add:

advanced-layout-library:
  version: 1.x
  css:
    theme:
      css/style.css: {}

For our needs we are using the frontend style sheet.

Clear your caches and the grid layouts are working within your admin theme.