Apex domains cannot have CNAME records.
Question and response
Question
dig secar.cz. NS
Answer
secar.cz. 5 NS ns1.secar.cz.
secar.cz. 5 NS ns2.secar.cz.
Authority
The response has no authority records.
Additional
ns1.secar.cz. 5 A 84.244.68.41
ns2.secar.cz. 5 A 82.99.137.41
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0