Code editor: Show design system focus ring on the title and content fields - #85468

What?

Part of #80138

In the Code editor, the title and content fields now show the same design system focus ring. The title no longer shows a doubled ring.

Why?

• The title field is a TextareaControl, which already draws the design system ring. The Code editor styles added a box-shadow ring and a theme-colored border on top of it, so it showed two rings.
• The content field used a legacy box-shadow ring, so the two fields looked different on focus.

How?

• Removed the title's focus override, so only TextareaControl's own ring shows.
• The content field uses outset-ring__focus() and resets the border color and box-shadow that wp-admin's forms.css applies on focus, matching how the design system's own text fields work.
• Removed the content field's border and box-shadow transition and its position: relative, which no longer have any effect.
• Increased PostTitleRaw's top margin from 2px to calc(2 * var(--wpds-border-width-focus)), so the ring isn't hidden under the sticky "Exit code editor" toolbar.

Testing Instructions

1. Open a post and switch to the Code editor (⋮ → Code editor).
2. Click the title field. There should be one ring with a small gap, and the border should stay gray.
3. Click the content field. It should look the same as the title.
4. Check the top edge of the title's ring. It should be fully visible below the "Exit code editor" toolbar.
5. Repeat in the Site Editor with a page.

Testing Instructions for Keyboard

1. In the Code editor, Tab from the "Exit code editor" button into the title field. It should show the focus ring.
2. Press Tab again to move to the content field. It should show the same ring.

Screenshots or screencast

Use of AI Tools

This PR was developed with the assistance of Claude Code.