Apex domains cannot have CNAME records.
Question and response
Question
dig hornaorava.sk. NS
Answer
hornaorava.sk. 5 NS dns.hornaorava.sk.
Authority
The response has no authority records.
Additional
dns.hornaorava.sk. 5 A 213.81.218.61
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0