[aaronrobertshaw]

Backport of Gutenberg PR WordPress/gutenberg#86240

Trac ticket: https://core.trac.wordpress.org/ticket/66468

Adds a transform block support with a single rotate feature. Blocks that opt in can be rotated by one angle. It outputs the rotate CSS property, not the transform shorthand, so existing block transforms still apply.

This PR backports:

• the new transform block support,
• transform.rotate in WP_Theme_JSON settings and styles, for blocks and block style variations only (not the root or elements),
• the transform.rotate style engine definition, limited to a single angle,
• rotate in safecss_filter_attr(), limited to a single angle,
• and the accompanying block supports, states, style engine, KSES and WP_Theme_JSON tests.

The block opt-ins (Group, Heading, Image and Video block.json), the transform.rotate setting in Core's theme.json and the editor UI arrive later with the Gutenberg package update.

Testing instructions

No Core block opts in yet, so test through theme.json styles.

1. In the active theme's theme.json, add "transform": { "rotate": "15deg" } under styles.blocks.core/group.
2. Also add "transform": { "rotate": "5deg" } at the top level of styles.
3. View a page that contains a Group block.
4. Check the global-styles-inline-css style tag contains :root :where(.wp-block-group){rotate: 15deg;}.
5. Check there is no rotate: 5deg rule. Root transforms are dropped.
6. Change the Group value to calc(10deg + 5deg) and confirm the rule disappears. Only a single angle is output.

Without this PR there is no rotate rule at all.

Use of AI

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 5
Used for: The mechanical port, tests and this description; I reviewed and edited the PR.

[github-actions]

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[github-actions]

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