Apex domains cannot have CNAME records.
Question and response
Question
dig selligent.stepstone.com. NS
Answer
selligent.stepstone.com. 5 NS ns-1649.awsdns-14.co.uk.
selligent.stepstone.com. 5 NS ns-732.awsdns-27.net.
selligent.stepstone.com. 5 NS ns-187.awsdns-23.com.
selligent.stepstone.com. 5 NS ns-1285.awsdns-32.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0