Apex domains cannot have CNAME records.
Question and response
Question
dig smart. NS
Answer
smart. 1 NS a.nic.smart.
smart. 1 NS b.nic.smart.
smart. 1 NS c.nic.smart.
smart. 1 NS d.nic.smart.
Authority
The response has no authority records.
Additional
a.nic.smart. 144406 A 194.169.218.70
b.nic.smart. 144406 A 185.24.64.70
c.nic.smart. 144406 A 212.18.248.70
d.nic.smart. 144406 A 212.18.249.70
a.nic.smart. 144406 AAAA 2001:67c:13cc:0:0:0:1:70
b.nic.smart. 144406 AAAA 2a04:2b00:13cc:0:0:0:1:70
c.nic.smart. 144406 AAAA 2a04:2b00:13ee:0:0:0:0:70
d.nic.smart. 144406 AAAA 2a04:2b00:13ff:0:0:0:0:70
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0