Hi,
in the dark theme when I add a custom field the menu for the type is not set in the the correct color, so only the selected text (one of “Text, Versteckt, Boolescher Wert, Verknüpft”) can be read; the rest is always in white.
In the light theme, there is no problem.
Not sure which version you are running, but i think it is already fixed in the latest web-vault.
I’m running Version 2.25.1 Vaultwarden in Docker on Synology
That is the web-vault version, but that version has indeed a bug which is fixed per 2.26.0.
That version is already included in the latest testing tagged version.