Twenty Twenty, Twenty Twenty-One: Let full-width Details blocks fill the editor width - #14738

Summary

In the block editor, a Details block set to full width stays at the narrow content width in Twenty Twenty and Twenty Twenty-One, while the front end is already correct.

The generic .wp-block { max-width: ... } editor rule also constrains the children of the Details block. This adds .wp-block-details > .wp-block { max-width: 100%; } to the editor styles of both themes, as suggested in the ticket. Margins and front-end styles are untouched.

• Twenty Twenty: editor-style-block.css and its RTL counterpart.
• Twenty Twenty-One: new details/_editor.scss partial imported in blocks-editor.scss, plus the compiled style-editor.css.

Testing instructions

1. Use Twenty Twenty or Twenty Twenty-One and add a Details block with some content in the editor.
2. Set its alignment to Full width.
3. Before: the block stays narrow in the editor. After: it fills the full width, matching the front end.

CSS-only change, so there is no automated test. I did not run a browser check of the editor.

Trac ticket: https://core.trac.wordpress.org/ticket/59957

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Sonnet 5.5
Used for: Implementation and PR description.

This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.