Apex domains cannot have CNAME records.
Question and response
Question
dig webstep.net. NS
Answer
webstep.net. 5 NS ns.webstep.cz.
webstep.net. 5 NS router.webstep.cz.
Authority
The response has no authority records.
Additional
ns.webstep.cz. 5 A 83.240.48.239
ns.webstep.cz. 5 A 84.242.97.14
router.webstep.cz. 5 A 94.130.126.19
ns.webstep.cz. 5 AAAA 2a02:830a:f03a:5b00:0:0:0:4
router.webstep.cz. 5 AAAA 2a01:4f8:10a:3718:0:0:0:19
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0