Headless Block Styles

Headless Block Styles brings full Gutenberg block styling to any headless frontend (e.g. Next.js) using the WordPress REST API — no WPGraphQL required.

It does two things:

1. Serves the global stylesheet (wp_get_global_stylesheet()): all --wp--preset--* CSS variables, preset classes (has-*-color, has-*-font-size, …), and theme/user styles — the CSS WordPress would normally enqueue on its own frontend.
2. Computes per-block inline styles on the server with the WordPress Style Engine and adds a block_data field to post REST responses, so your frontend receives ready-to-spread React style objects instead of deriving them from raw block attributes in JavaScript.

REST API

GET /wp-json/headless-block-styles/v1/stylesheet

• types — comma-separated subset of variables,presets,styles,base-layout-styles. Omit for all.
• format — json (default) or css (raw CSS, usable directly in a <link> tag).

GET /wp-json/headless-block-styles/v1/theme

Returns merged theme.json settings (wp_get_global_settings()) — color palette, font sizes, layout sizes.

block_data field on posts and pages

Every REST-enabled post type response gains a block_data field: the parsed block tree where each block carries inlineStyles (camelCase, ready for a React style prop), classNames (editor-parity has-* classes), attributes, innerHTML, and recursive innerBlocks.

inlineStyles covers the `style` attribute (spacing, borders, typography, colors — via the WP Style Engine), preset attributes (`backgroundColor`, `textColor`, `gradient`, `borderColor`, `fontSize`, `fontFamily`), and layout (`width`, `height`, `layout.contentSize/wideSize/justifyContent`).

rendered_blocks field on posts and pages

For rendering WordPress’s HTML faithfully: returns html, css, and svg — the rendered block markup together with the block-support CSS WordPress generates at render time (layout container rules, element link/button colors, duotone filters) and the duotone SVG definitions. On a normal WordPress frontend this CSS is printed in a <style> tag and never reaches REST consumers; here it is captured from the same render as the returned HTML so the generated class names always match.

Not needed on a request? Exclude fields: /wp/v2/posts?_fields=id,title,content.

Filters

• headless_block_styles_block_inline_styles — modify a block’s computed style object. Args: $styles, $attrs.
• headless_block_styles_block_class_names — modify a block’s computed class names. Args: $classnames, $attrs.
• headless_block_styles_post_types — which post types get the block_data field.

Full documentation and Next.js usage examples: github.com/FuSan21/headless-block-styles