[5.1] UI issue on MFA in Dark Mode

[dautrich]

Steps to reproduce the issue

1. Prepare a J5.1 website with a backend user configured to use multiple MFA options (i.e. Passkey as default, TOTP, Backup Codes).
2. Switch backend to Dark Mode.
3. Logout and login again with the backend user from 1. by entering userid and password.
4. On screen “Multifactor Authentication” click “Select a different method”

Expected result

Captions on the following screen are clearly legible.

Actual result

Captions on the following screen are not legible:

System information (as much as possible)

J5.1.0 (local via Laragon)
Apache 2.4.59
PHP 8.3.8
MySQL 8.0.36

Additional comments

[brianteeman]

The work done in #41799 was not complete and needs to be repeated for administrator\components\com_users\tmpl\captive\select.php