Apex domains cannot have CNAME records.
Question and response
Question
dig satoya.cz. NS
Answer
satoya.cz. 5 NS ns.satoya.cz.
satoya.cz. 5 NS bt.satoya.cz.
Authority
The response has no authority records.
Additional
bt.satoya.cz. 5 A 212.24.129.94
ns.satoya.cz. 5 A 94.142.233.142
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0