I've never seen Galaxus/Digitec offer lightning delivery. If you're referring to deliveries that are delivered the following day up to Saturday (depending on the option you choose) when you order before 19:00, I can confirm that these deliveries have always arrived packed in a cardboard box. Maybe this is also the lightning express you are referring to.

The products are shipped in a Galaxus box:
https://www.galaxus.ch/de...

Does this also apply if the parcel is delivered via flash delivery? Then these are usually without an additional box or are they then also delivered discreetly?