Apex domains cannot have CNAME records.
Question and response
Question
dig belleville.cz. NS
Answer
belleville.cz. 4 NS ns1.websupport.cz.
belleville.cz. 4 NS ns3.websupport.eu.
belleville.cz. 4 NS ns2.websupport.cz.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0