Exported MPR wrapped legacy components lose styles

[OlliTietavainenVaadin]

Description of the bug

When I have a V8 component with MPR's LegacyWrapper, I can use it without problems in a Flow view. If I try to use the same component in a React view via WebComponentExporter, the component appears and reacts to events as expected but doesn't have any styles.

Expected behavior

Legacy styles should be shown

Minimal reproducible example

https://github.com/vaadin/hackathon-24-4/tree/olli

Versions

• Vaadin / Flow version: 24.4.beta4
• Java version: 21
• OS version: Windows 11
• Browser version (if applicable): Chrome (latest)
• Application Server (if applicable): Spring Boot
• IDE (if applicable): IntelliJ Idea

[mshabarov]

This issue isn't in newly introduced ReactAdapterElement or related API, but in between Embedded Flow and MPR features (i.e. WebComponentExporter and LegacyWrapper).

I can confirm that if I take Flow 24.3 branch and add a legacy components into exported web-component, I'll get no styling either.