[Bug]: Minor: PDF Preview in Darkmode has Black Background

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

In Darkmode the Preview of PDFs Changes the Background of PDFs from white to Black.
This only applies to Text (Black on white), pictures are not affected.
Lightmode:

Darkmode:

Steps to reproduce

1. Upload PDF with plain text
2. Upload PDF with pictures e.g. book with colored cover
3. Change to Darkmode
4. Check Preview Icons

Expected behavior

No Changes to Previews

Nextcloud Server version

30

Operating system

None

PHP engine version

None

Web server

None

Database engine version

None

Is this bug present after an update or on a fresh install?

None

Are you using the Nextcloud Server Encryption module?

None

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

List of activated Apps

Nextcloud Signing status

Nextcloud Logs

Additional info

No response

Reproduce the issue with a text-only PDF and an image-containing PDF while switching between light and dark mode, then trace the PDF preview rendering and theme handling. Done means text-based PDF previews retain their original white background in dark mode while image previews remain unaffected.