How to set mysql system variables such as max_allowed_packet max_allowed_packet, character_set_server and collation-server through Dockerfile?

I am using Docker for mysql. Need to set the system variables such as max_allowed_packet, character_set_server and collation-server of mysql in the Dockerfile. I tried with the below commands providing in the Dockerfile. but its not working.

Dockerfile:

FROM mysql:latest
VOLUME /opt/data:/var/lib/mysql
ENV MYSQL_ROOT_PASSWORD password
RUN sed -i 's/^max_allowed_packet.*/max_allowed_packet = 1073741824/' /etc/mysql/my.cnf
RUN sed -i "/\[mysqld]/a character-set-server=utf8mb4" /etc/mysql/my.cnf
RUN sed -i 's/^collation-server.*/collation-server = utf8mb4_unicode_ci/' /etc/mysql/my.cnf 
CMD ["mysqld"]

Build command:

sudo docker build -t mysqltest:1 .

Run command:

sudo docker run -p 3306:3306 -restart=always -d mysqltest:1