Apex domains cannot have CNAME records.
Question and response
Question
dig viwefix.cz. NS
Answer
viwefix.cz. 5 NS tns.viwefix.cz.
viwefix.cz. 5 NS dns.viwefix.cz.
viwefix.cz. 5 NS sns.viwefix.cz.
Authority
The response has no authority records.
Additional
dns.viwefix.cz. 5 A 81.0.235.1
sns.viwefix.cz. 5 A 93.185.100.244
tns.viwefix.cz. 5 A 85.132.152.123
dns.viwefix.cz. 5 AAAA 2001:1528:132:0:0:0:0:60
sns.viwefix.cz. 5 AAAA 2a00:1ed0:46:200:0:0:1212:247
tns.viwefix.cz. 5 AAAA 2a02:e98:20:1600:0:0:0:e0
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0