Apex domains cannot have CNAME records.
Question and response
Question
dig superhosting.cz. NS
Answer
superhosting.cz. 5 NS ns1.superhosting.cz.
superhosting.cz. 5 NS ns2.superhosting.cz.
Authority
The response has no authority records.
Additional
ns1.superhosting.cz. 5 A 95.168.195.129
ns2.superhosting.cz. 5 A 88.86.116.42
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0