This is how I containerize applications. I used this site for help and inspiration.
$ sudo pacstrap -i -c -d ~/chromium base chromium --ignore linux
$ sudo systemd-nspawn -u root -D ~/chromium/ bash
root # useradd chris -m
root # su -l chris && cd
$ mkdir -p mnt/pulse mnt/gdm
$ ^d
root # passwd chris
$ sudo systemd-nspawn -D ~/Containers/chromium/ \
--bind-ro /run/user/1000/gdm/:/home/chris/mnt/gdm \
--setenv=PULSE_SERVER=unix:/home/chris/mnt/pulse/native \
--setenv XAUTHORITY=/home/chris/mnt/gdm/Xauthority \
--setenv DISPLAY=$DISPLAY \
--bind /dev/snd/ \
--bind /run/user/1000/pulse/:/home/chris/mnt/pulse \
--bind /tmp/.X11-unix/ \
--bind /dev/shm \
--bind /etc/machine-id -u chris chromium