Day 2:
Yes, @coloneljethro gave me an excellent suggestion to make openings on the side. But first I went through all the better electrical stores this morning. I tried to explain to them what I needed and I felt like I was buying an island and not a LED strip.
I made the holes, cut out the upper part that made the shadow, trimmed the edges a bit (covered them with tape), and covered the box with completely new baking paper :)
After all, I needed only one first-aid bandage tape.

I did buy something though for $3

I made a lamp and placed it on a stand of an old broken one that easily bends in all directions.

It didn't turn out bad at all!!!

@alt3r this weekend, I will take beautiful photos in the daylight.
And I will definitely use the box...sometimes.