Apex domains cannot have CNAME records.
Question and response
Question
dig explore-blue.com. NS
Answer
explore-blue.com. 5 NS ns53.domaincontrol.com.
explore-blue.com. 5 NS ns54.domaincontrol.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0