I have seen user struggles with this for along period of time. Hence, I am posting this and hopefully, it helps in nailing the issue faster. However, not all Linux will need to address this. I do not recalled default installation of Oracle 12C on Red Hat needs to address this at all only Centos. I could be wrong.
Inside the Oracle Database VM.
https://<ip address>:5500/em
https://<ip address>:5500/em
Outside of the VM, unable to connect. Pretty obvious, this is an indication that there are some sort of firewalls issues either from the VM itself or the host layer if the VM can be ping-ed and ssh-ed into.
In the VM check the firewalls HTTPS and ports.
Accessible now.
