How to acces Docker container files?

Hi Im total newbie but I tried to run website from github on localhost that use Docker, It works but I dont know where are website .css files because I wanted to change few things , I guess the files that website is using are stored in one of the containers right? Thats what shows after docker ps -a command:

CONTAINER ID IMAGE a7cb80f63c7c joe_app be4121930870 joe_varnish 5369df6d616c nginx:1.13-alpine 5eccea787348 rabbitmq:alpine 175bab5538d9 postgres:9.6 -alpine 9a0ef4a9d506 joe_app a0fb821afff7 memcached:1.4-alpine a6feeb4c1bdb joe_worker 654a70807bd0 joe_assets ffbf2b33a2b2 debian 8d2eb3494f5f hello-world

I thought the files might be in Image "joe_assets" but when I try to acces it ,thats the message I receive from terminal: sudo docker exec -it 654a70807bd0 /bin/bash

"Error response from daemon container is not running.