Apex domains cannot have CNAME records.
Question and response
Question
dig static.wline.lns.sme.cust.swisscom.ch. NS
Answer
static.wline.lns.sme.cust.swisscom.ch. 5 NS adnso2.bluewin.ch.
static.wline.lns.sme.cust.swisscom.ch. 5 NS adnsz2.bluewin.ch.
static.wline.lns.sme.cust.swisscom.ch. 5 NS adnso1.bluewin.ch.
static.wline.lns.sme.cust.swisscom.ch. 5 NS adnsz1.bluewin.ch.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0