Resize Video and/or Image in mobile view

Site URL: https://www.portanova.pt/

Hello...I want to have a slideshow of images on main page. Because I also liked the social media buttons I decided to add a video as section's background. However in mobile view the video gets cutted. Also tried changing it to images but the same thing happens. How can a video / or iamge be resized on mobile view so it doesnt get cutted?

Thankyou