Since version v1.33.0 you can modify the CSS which Vaultwarden previously embedded in the web-vault.
This way it makes it more easier for users to tweak the style and layout or even hide items.

To modify the CSS you need to add a templates directory in your data directory, or provide the correct path via the TEMPLATES_FOLDER environment variable.
Within this directory you need to create another directory called scss which will hold the file(s) for modifying the stylesheet Vaultwarden will serve.