Learning by doing: How to change the folder in docker compose (vaultwarden)

Hi! I am running a vaultwarden-docker and would like to change the folder where the credentials are stored. This is my current docker-compose-file:

version: '3.4'

services:

vaultwarden:

image: vaultwarden/server:latest

restart: always

ports:

  - '127.0.0.1:8200:80'

volumes:

  - ./vaultwarden:/data/

So my credentials are stored in a folder called vaultwarden in the root of the server.

a) How can i change this folder in the stack-file of portainer without loosing the data?

b) Where would the folder be when i would write "vaultwarden" without the "./"? In the /root-folder?

Sorry for the noob-questions but the docker-tutorials i found are much too high for me. ;)