Avoid hiding all non-storybook body children

[IanVS]

Fixes #343

This replaces the blunt hammer of

body > * {
  display: none !important;
}

with something a bit more nuanced, taken from the storybook default head styles.

This is only necessary until vitejs/vite#7786 is released, then we can remove the workaround and ask users to update vite in order to avoid this flash.

[IanVS]

@eirslett @joshwooding while exploring this, I realized that the html provided to transformIndexHtml in code-generator-plugin.ts is already transformed, due to iframeMiddleware in the index.ts file. Do either of you know why it's included in code-generator-plugin.ts, given this is the case?

[joshwooding]

@eirslett @joshwooding while exploring this, I realized that the html provided to transformIndexHtml in code-generator-plugin.ts is already transformed, due to iframeMiddleware in the index.ts file. Do either of you know why it's included in code-generator-plugin.ts, given this is the case?

I'm not too sure 😕

[IanVS]

Going to merge, but I'd still be curious to hear if Eirik knows the reason for this. I think we can probably remove it in a separate PR.

[eirslett]

I'm not sure 🤷 it's probably fine to change it.