Apex domains cannot have CNAME records.
Question and response
Question
dig pixelpark.net. NS
Answer
pixelpark.net. 5 NS ns3.pixelpark.de.
pixelpark.net. 5 NS ns4.pixelpark.de.
pixelpark.net. 5 NS ns1.pixelpark.de.
pixelpark.net. 5 NS ns2.pixelpark.de.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0