EPUBs are not readable with new dark mode

[thornbill]

Describe The Bug EPUBs seem to render with black text on a dark background by default since https://github.com/jellyfin/jellyfin-web/pull/3855 was merged.

Steps To Reproduce

1. Open the EPUB player within Jellyfin

Expected Behavior Book text should be legible. We should either:

1. Use epub.js theme support to render in dark mode correctly.
2. Force a light background for the EPUB reader.

Preferably we should use epub.js themes in my opinion. I have not found much documentation for that though.

Logs N/A

Screenshots

System (please complete the following information):

• Platform: Any
• Browser: Any
• Jellyfin Version: Unstable

Additional Context

[carif]

Oh.

Preferably we should use epub.js themes in my opinion. I have not found much documentation for that though.

I think the only documentation is that example here. It just registers some css file. I'm not sure how this would be implemented in Jellyfin, but I guess when Jellyfin changes the theme, epubjs needs to be somehow informed of that change.

Based on that, we need to do something like:

// register css themes with epubjs.. 
// pls mind that this code causes "MIME type (“text/html”) mismatch" that needs to be fixed (idk how) 
rendition.themes.register('dark', 'style.scss');
rendition.themes.register('light', 'style.scss');

// somehow select the theme based on which theme jellyfin uses
rendition.themes.select('dark');

Using style.scss assumes that someone puts a proper light and dark theme into there. When setting the background css value, epubjs will only style the book, not any other background that might exists there.