Apex domains cannot have CNAME records.
Question and response
Question
dig runbox.com. NS
Answer
runbox.com. 5 NS dns63.copyleft.no.
runbox.com. 5 NS dns62.copyleft.no.
runbox.com. 5 NS dns61.copyleft.no.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0