Apex domains cannot have CNAME records.
Question and response
Question
dig tango.hr. NS
Answer
tango.hr. 5 NS dns1.cdn.hr.
tango.hr. 5 NS dns2.cdn.hr.
Authority
The response has no authority records.
Additional
dns1.cdn.hr. 5 A 188.165.36.208
dns2.cdn.hr. 5 A 185.58.73.222
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0