Mobile background not showing up at all

Site URL: https://www.gramm00.com/

I've created a separate section for mobile on the homepage and about page of this site. The background shows up perfectly in the mobile preview within Squarespace but when I open the site on my phone the background shows up as black.

I have tried removing all my custom css and opening it again and it still shows up as black so it's not something I've done, could someone please help me?

Attached are two images, how it appears in the mobile window within squarespace and how it appears on my phone.

Hey Tuanphan! 

Thanks so much for getting back to me sorry I missed it! I did fix it thanks. But I've got a different issue now which I've asked over here:

https://forum.squarespace.com/topic/245909-adding-autoplay-videos-to-portfolio/

Wondering if you could help with this at all?

Thanks so much for everything you do on this forum!