Code on how to make the website horizontal on mobile?

Site URL: http://lassement.com/

Hello,

I just created a website for my portfolio (lassement.com)

The website looks great on desktop however on mobile it skips images when you go from slide to slide.

If I alter the size on the squarespace app it also alters the size of the website to make the mobile one seem alright.

If theres any CSS code I can use to make the site appear horizontal on the mobile app while staying the same on the website that would be amazing.

Thank you 

Aleksandar