Custom HTML, scoped CSS, and editing boundaries

Documentation / Design and styling

Custom page source is a reviewed HTML fragment with scoped CSS and supported behavior declarations. It is not a whole document and does not provide unrestricted access to the page runtime.

Edit the stored source

Where available, open the advanced source area under Custom design. The current controls expose SVG and HTML source, Scoped CSS, Save custom source, and Cancel source changes. Review the existing source before replacing it. The source save uses the current page revision and can reject a stale edit.

The visual editor treats custom bodies, custom headers, and shared shell regions as read-only. It preserves stored source rather than reconstructing it from behavior-modified browser markup. Do not use the visual editor to overwrite custom content with native blocks.

Respect validation

Only supported tags, attributes, URLs, CSS, and declared behavior modules are accepted. Scripts, inline event handlers, and whole-document HTML are outside the contract. IDs must be unique and begin with the fragment prefix, such as cb-body- for a body section identified as body.

Custom headers have additional title-binding rules. Keep the real page header and canonical title rather than hard-coding an unrelated main heading into the body.

Supported native form or other object placeholders render engine components inside the custom layout. They do not authorize arbitrary form markup or bypass site configuration.

Review the saved output

Validation confirms the source contract, not the quality of the design. Check responsive layout, reading order, focus, contrast, links, media, and reduced motion. A failed save is an error to resolve, not evidence that unsupported content was safely accepted.

See Page anatomy and the managed editor for the native alternative.