Custom properties do not work in some cases

[lyswhut]

Describe the bug

I have a custom react-like Portal component, custom properties don't work in the Portal component.

Is there something wrong with my usage or is it a bug?

Reproduction

REPL

Logs

System Info

Svelte 5.25.3
Chrome

Severity

annoyance

[Conduitry]

<Portal> places its children as another top-level element in the main body of the document, so they are unaffected by the --width="200px". CSS custom properties in Svelte inherit the way they do in HTML - from parent elements in the DOM to child elements.