Apex domains cannot have CNAME records.
Question and response
Question
dig savvy.cz. NS
Answer
savvy.cz. 5 NS ns1.savvy.cz.
savvy.cz. 5 NS ns2.savvy.cz.
Authority
The response has no authority records.
Additional
ns1.savvy.cz. 5 A 193.19.176.160
ns2.savvy.cz. 5 A 37.205.14.48
ns1.savvy.cz. 5 AAAA 2001:67c:22f8:101:0:176:160:1
ns2.savvy.cz. 5 AAAA 2a03:3b40:fe:8b3:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0