Mobile rotation - white stripes on each side

Hello dear Bubble community,

I am currently building an app with bubble new responsive design,
I deployed a first version of the app and thought I did well but it appears than when I flip my phone around (horizontal mode) there are white stripes on each side of the phone as shown on the screen down below:

My background color is black while the stripes are white, where could this problem be from ?

Thanks a lot for your precious answers !

Do you have a max width set on the black group?

There is no max width on any containers in the page
The only width that is limited is fixed on 100% of the parent group which shouldn’t cause any problem

Is there a way to upload videos to the forum so I could show you?

What is the answer to this?