Apex domains cannot have CNAME records.
Question and response
Question
dig CARNet.hr. NS
Answer
CARNet.hr. 5 NS ns2.IPv6.CARNet.hr.
CARNet.hr. 5 NS dns2.CARNet.hr.
CARNet.hr. 5 NS ns1.IPv6.CARNet.hr.
CARNet.hr. 5 NS dns1.CARNet.hr.
Authority
The response has no authority records.
Additional
dns1.carnet.hr. 5 A 161.53.123.2
dns2.carnet.hr. 5 A 161.53.160.2
dns1.carnet.hr. 5 AAAA 2001:b68:ff:2:0:0:0:2
dns2.carnet.hr. 5 AAAA 2001:b68:ff:1:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0