Improve Admin interface in layout editor page

Problem/Motivation

VLSuite mixes two themes (admin and main theme) in the edit layout page so the admin interface is rendered using the admin theme. This was ok until Drupal core 10.1 landed, see 🐛 Layout Builder modal dialog is broken with Drupal 10.1+ Fixed . In that issue a workaround was added: disable CSS/JS aggregation in the edit layout pages.

This issue is here to provide a better fix. Ideally, be able to mix both themes. See comment #3 🐛 Layout Builder modal dialog is broken with Drupal 10.1+ Fixed from that issue with some ideas.

The present issue would be resolved when core solves #2195695: Admin UIs on the front-end are difficult to theme → , but it is good to have it open here so we don't forget it when core solves the problem,

Steps to reproduce

See 🐛 Layout Builder modal dialog is broken with Drupal 10.1+ Fixed .

Proposed resolution

Wait for core to solve it or try our own approximation.

Remaining tasks

TBD.

User interface changes

TBD.

API changes

TBD.

Data model changes

TBD.