Basic security question) What do I do with "rootCA-key.pem" file

[upstroke-version]

Thanks to mkcert, I've successfully setup certificates for my home server.
But now I have "rootCA-key.pem" and "rootCA.pem" file just sitting at CAROOT directory.
After basic googling "rootCA.pem" doesn't seem that important to keep it secure so I'm going to leave it there, but "rootCA-key.pem" file seems pretty important to secure it.
Do I just leave it there and just don't do any stupid things like downloading malware, or is it better to move to some sort of encrypted conatiner, can macOS keychain securely store it? If "rootCA-key.pem" isn't present in CAROOT directory due to moving to better place, does mkcert still work as before without issue?