Fix #56818: Toggle 2FA icons based on theme light/dark mode

[carolinafquinteiro]

The 2FA setup and backup code icons were not adapting correctly to different themes, leading to visibility issues.

This fix replaces the single static icon with two separate icons: .two-factor-icon-light and .two-factor-icon-dark. It introduces a new SCSS file to toggle visibility based on:

• The 'data-themes' attribute on the body (manual selection).
• The 'prefers-color-scheme' media query (system default theme).

Changes:

• Modified 2FA PHP templates to include light and dark SVG versions.
• Added twofactor-icons.scss to handle display:none/inline logic.
• Registered the new stylesheet in the relevant 2FA views.

• Resolves: [Bug]: The icons for 2FA providers remain white regardless of whether the theme is dark or light #56818

Summary

TODO

• ...

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI

[susnux]

Thank you very much for your contribution!

One question about the implementation:
Why not simplify by just assign this stlye to the icon:

filter: var(--background-invert-if-dark);

[miaulalala]

Thanks for your contribution @carolinafquinteiro - could you add some before / after screenshots?

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[carolinafquinteiro]

Thank you for the suggestion @susnux! I've tested using filter: var(--background-invert-if-dark); but unfortunately it didn't work as expected: the icon remained light even in dark mode. It seems that in this specific guest/login context, the filter isn't being triggered correctly or the variable isn't behaving as intended for these specific assets. That's why I kept the current implementation to ensure it works reliably across all themes.

[carolinafquinteiro]

Hi @miaulalala,

Thank you for your feedback. As requested, here are the screenshots showing the visibility issue and the fix I implemented.

In the first image, you can see that the icon is nearly invisible due to the white-on-white contrast. My PR ensures the icon remains visible by correctly switching between the light and dark versions.

Issue (White on White):

Corrected:

[miaulalala]

Fantastic - can you rebase your PR on the most current master please?