Apex domains cannot have CNAME records.
Question and response
Question
dig cention.se. NS
Answer
cention.se. 5 NS ns-1890.awsdns-44.co.uk.
cention.se. 5 NS ns-748.awsdns-29.net.
cention.se. 5 NS ns-403.awsdns-50.com.
cention.se. 5 NS ns-1292.awsdns-33.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0