On server:

ss-server -s 0.0.0.0 -s ::0 -p 443 -k shadowsocks-password -m
aes-128-gcm -U # change to lowercase u if you want to be able to
connect to the server over TCP too.

On client:

ss-tunnel -s shadowsocks-server -p 443 -l 51820 -L
wireguard-server:51820 -k shadowsocks-password -m aes-128-gcm -U

Connect WireGuard to 127.0.0.1:51820. Done.