Apex domains cannot have CNAME records.
Question and response
Question
dig netforms.cz. NS
Answer
netforms.cz. 4 NS hostbase.netforms.cz.
netforms.cz. 4 NS ns2.netforms.cz.
netforms.cz. 4 NS secondary.edera.cz.
Authority
The response has no authority records.
Additional
ns2.netforms.cz. 4 A 80.211.223.196
hostbase.netforms.cz. 4 A 91.222.52.52
secondary.edera.cz. 4 A 37.157.197.66
ns2.netforms.cz. 4 AAAA 2001:15e8:110:5ec4:0:0:0:1
secondary.edera.cz. 4 AAAA 2a02:2b88:6:2dd6:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0