Apex domains cannot have CNAME records.
Question and response
Question
dig coolcatmail.com. NS
Answer
coolcatmail.com. 5 NS coco.bunny.net.
coolcatmail.com. 5 NS kiki.bunny.net.
Authority
The response has no authority records.
Additional
coco.bunny.net. 5 A 109.104.147.1
kiki.bunny.net. 5 A 91.200.176.1
coco.bunny.net. 5 AAAA 2400:52e0:fff2:0:0:0:0:1
kiki.bunny.net. 5 AAAA 2400:52e0:fff0:0:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0