Apex domains cannot have CNAME records.
Question and response
Question
dig port53.se. NS
Answer
port53.se. 5 NS pdns03.port53.se.
port53.se. 5 NS pdns01.port53.se.
port53.se. 5 NS pdns02.port53.se.
Authority
The response has no authority records.
Additional
pdns01.port53.se. 5 A 83.233.26.30
pdns02.port53.se. 5 A 82.209.164.246
pdns03.port53.se. 5 A 88.131.87.90
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0