Apex domains cannot have CNAME records.
Question and response
Question
dig eisif.cz. NS
Answer
eisif.cz. 5 NS hostbase.netforms.cz.
eisif.cz. 5 NS secondary.edera.cz.
Authority
The response has no authority records.
Additional
hostbase.netforms.cz. 5 A 91.222.52.52
secondary.edera.cz. 5 A 37.157.197.66
secondary.edera.cz. 5 AAAA 2a02:2b88:6:2dd6:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0