[Bug]: Styles slightly broken on login flow for older Android Webview versions

⚠️ 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 (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• Nextcloud Server is running on 64bit capable CPU, PHP and OS.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

This is a follow up for #36934. #37005 fixed the login failure but the styles still look strange in older webview versions. This is most noticeable on primary color buttons (missing the color) and text fields (wrong width). See screenshots below for comparison.

It looks fine on 25.0.1 but not 25.0.4 or master. It also looks fine on newer Webview versions but not on older Webview versions.

Screenshots

Old webview (nc 25.0.4/master)	Old webview (nc 25.0.1)	New webview (nc 25.0.4/master)

Steps to reproduce

1. Set up 25.0.4 or master server
2. Try to log in with the Android app on an older device
3. See strange styles in

Expected behavior

Normal styles 🤷

Installation method

None

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

No response

List of activated Apps

-

Nextcloud Signing status

No response

Nextcloud Logs

nextcloud.log

Additional info

Tested Webview versions:

• Broken styles: 66.0.3359.158 (on Android 9)
• Correct styles: 101.0.4951.74 (on Android 13)

Console logs of the webview when styles are wrong (server master):
toaster.lan-1678273224246.log

Start by reproducing the login flow on the listed older and newer Android WebView versions, using the screenshots and console log linked in the issue for comparison. Done means the primary-color buttons and text fields render normally on older WebViews as well as newer versions.