I have seen multiple example for two approaches for setting environment variables in docker-compose.yml files

environment:
      EUREKA_CLIENT_SERVICEURL_DEFAULTZONE: http://eureka-server:9000/eureka

or

environment:
     - EUREKA_CLIENT_SERVICEURL_DEFAULTZONE=http://eureka-server:9000/eureka

is there a right or wrong approach ?
which one should be prefferred ?