Oh yes, you are correct.
The card is only directly available in the material and classic themes as far as I can see.
You may be able to use Anvil’s “roles” and/or CSS to add a shadowed effect.
Unfortunately changing a component’s role in the IDE seems to only be possible in the classic and material themes (someone please correct me if I am wrong as I cannot find a way).
Where it is possible, here’s an example of the CSS:
.anvil-role-my_shadowed_component {
box-shadow: 0 2px 2px 0 rgba(0, 0, 0, 0.14), 0 3px 1px -2px rgba(0, 0, 0, 0.2), 0 1px 5px 0 rgba(0, 0, 0, 0.12);
}