Cards shouldn't be base

### Is there an existing issue outlining your problem?

- [X] I have searched the existing issues and they do not solve my problem.

### Describe your issue.

In my opinion cards should be mantle or surface0, because at the moment there is just a drop shadow but the background colour is the same which looks a bit weird.

Example:

Start by searching the SCSS theme styles for the card selectors and checking how they currently use the base color. Compare the rendered cards with mantle and surface0, then verify that the chosen color separates cards from the background without losing the intended drop shadow.

Written by the indexing model from the issue text.